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MicroRNAs (miRNAs) are regulators of gene expression, and their dysregulation is linked to cancer and other diseases, making them important therapeutic targets. Several strategies for targeting and modulating miRNA activity are being explored. For example, steric-blocking antisense oligonucleotides (ASOs) can reduce miRNA activity by either blocking binding sites on specific mRNAs or base-pairing to the miRNA itself to prevent its interaction with the target mRNAs. ASOs have been less explored as a tool to elevate miRNA levels, which could also be beneficial for treating disease. In this study, using the PKD1 /miR-1225 gene locus as an example, where miR-1225 is located within a PKD1 intron, we demonstrate an ASO-based strategy that increases miRNA abundance by enhancing biogenesis from the primary miRNA transcript. Disruptions in PKD1 and miR-1225 are associated with autosomal dominant polycystic kidney disease (ADPKD) and various cancers, respectively, making them important therapeutic targets. We investigated PKD1 sequence variants reported in ADPKD that are located within the sequence shared by miR-1225 and PKD1, and identified one that causes a reduction in miR-1225 without affecting PKD1 We show that this reduction in miR-1225 can be recovered by treatment with a steric-blocking ASO. The ASO-induced increase in miR-1225 correlates with a decrease in the abundance of predicted miR-1225 cellular mRNA targets. This study demonstrates that miRNA abundance can be elevated using ASOs targeted to the primary transcript. This steric-blocking ASO-based approach has broad potential application as a therapeutic strategy for diseases that could be treated by modulating miRNA biogenesis., (© 2024 Havens et al.; Published by Cold Spring Harbor Laboratory Press for the RNA Society.)

Numerous neurological disorders are linked to sequences rich in guanine repeats found in introns, exons, and regulatory regions of genes. These sequences have been observed to form stable G-quadruplex (GQ) structures both in vitro and in vitro. Cerebellar Ataxia with Neuropathy and Vestibular Areflexia Syndrome (CANVAS), a slowly progressive neurodegenerative disorder, is associated with the biallelic expansion of (AAGGG) n pathogenic repeats in the second intron of the RFC1 gene. Though these G-rich pathogenic repeats in other neurological diseases are associated with protein loss of function, RNA gain of function, and/or protein gain of function, not much is known about the pathological mechanism associated with CANVAS. Herein, we report the formation of stable GQ conformations in the CANVAS-associated repeats i.e., r(AAGGG) n , where 'r' stands for RNA. These GQs are critical regulators in neurological disorders leading to RNA foci formation and RNA binding protein sequestration. They also alter other causative processes like intron retention, which leads us to hypothesize a toxic Proteinopathy mechanism in CANVAS. Various biophysical and biomolecular assays characterized the interactions of three aggregation-prone RNA-binding proteins (RBPs): heterogeneous nuclear ribonucleoprotein H1/F (hnRNP H1/F), and DGCR8 with different pathogenic repeats [(AAGGG) 9 ] in vitro, further affirming the hypothesis. The biophysical observations are further supported by molecular dynamics analysis and cell-based studies, putting us a step closer to elucidating the pathological mechanism(s) in CANVAS neuropathy, paving the way for the development of innovative therapeutic interventions., Competing Interests: Declarations Competing interests The authors declare no competing interests., (© 2024. The Author(s).)

Background: Autosomal Recessive Polycystic Kidney Disease (ARPKD) is a rare hereditary disorder caused by variants in PKHD1. Currently, aberrant splicing has been reported to play important roles in genetic disease. Our goal is to analyze intronic variants in PKHD1 at the mRNA level., Results: The 12 candidate variants were introduced into the corresponding minigene and functionally assayed in HEK 293T and Hela cells. We identified 11 variants that induce splicing alterations, resulting in various consequences such as skipping of exons, intron retention and protein truncation., Conclusions: This underlined the importance of mRNA-level assessment for genetic diagnostics in related genetic disorders., (© 2024. The Author(s).)

Dedicator of cytokinesis 8 (DOCK8) deficiency underlies the majority of cases of patients with autosomal recessive form of the hyper-immunoglobulin E syndrome (HIES). Most DOCK8 mutations involve deletions and splice junction mutations that abrogate protein expression. However, a few patients whose presentation is reminiscent of DOCK8 deficiency have no identifiable mutations. Using Whole Exome Sequencing (WES), we identified a deep intronic homozygous DOCK8 variant located in intron 36 (c.4626 + 76 A > G) in two unrelated patients with features of HIES that resulted in an in-frame 75 base pair intronic sequence insertion in DOCK8 cDNA, resulting in a premature stop codon (p.S1542ins6Ter). This variant resulted in variable decrease in DOCK8 expression that was associated with impaired T cell receptor-triggered actin polymerization, decreased IL-6-induced STAT3 phosphorylation, reduced expression of the Th17 cell markers CCR6 and IL-17, and higher frequencies of GATA3 + T cells indicative of Th2 skewing. Our approach extends the reach of WES in identifying disease-related intronic variants. It highlights the role of non-coding mutations in immunodeficiency disorders, including DOCK8 deficiency, and emphasizes the need to explore these mutations in unexplained inborn errors of immunity., (Copyright © 2024 Elsevier Inc. All rights reserved.)

The diagnosis of mitochondrial disorders is complex. Rapid whole genome sequencing is a first line test for critically ill neonates and infants allowing rapid diagnosis and treatment. Standard genomic technology and bioinformatic pipelines still have an incomplete diagnostic yield requiring complementary approaches. There are currently limited options for rapid additional tests to continue a diagnostic work-up after a negative rapid whole-genome sequencing result, reflecting a gap in clinical practice. Multi-modal integrative diagnostic approaches derived from systems biology including proteomics and transcriptomics show promise in suspected mitochondrial disorders. In this article, we report the case of a neonate who presented with severe lactic acidosis on the second day of life, for whom an initial report of ultra-rapid genome sequencing was negative. The patient was started on dichloroacetate as an emergency investigational new drug (eIND), with a sharp decline in lactic acid levels and clinical stabilization. A proteomics-based approach identified a complete absence of PDHX protein, leading to a re-review of the genome data for the PDHX gene in which a homozygous deep intronic pathogenic variant was identified. Subsequent testing in the following months confirmed the diagnosis with deficient pyruvate dehydrogenase enzyme activity, reduced protein levels of E3-binding protein, and confirmed by mRNA sequencing to lead to the inclusion of a cryptic exon and a premature stop codon. This case highlights the power of rapid proteomics in guiding genomic analysis. It also shows a promising role for dichloroacetate treatment in controlling lactic acidosis related to PDHX-related pyruvate dehydrogenase complex deficiency., (Copyright © 2024 Elsevier B.V. and Mitochondria Research Society. All rights reserved.)

In Huntington's disease (HD), aberrant processing of huntingtin (HTT) mRNA produces HTT1a transcripts that encode the pathogenic HTT exon 1 protein. The mechanisms behind HTT1a production are not fully understood. Considering the role of m 6 A in RNA processing and splicing, we investigated its involvement in HTT1a generation. Here, we show that m 6 A methylation is increased before the cryptic poly(A) sites (IpA1 and IpA2) within the huntingtin RNA in the striatum of Hdh+/Q111 mice and human HD samples. We further assessed m 6 A's role in mutant Htt mRNA processing by pharmacological inhibition and knockdown of METTL3, as well as targeted demethylation of Htt intron 1 using a dCas13-ALKBH5 system in HD mouse cells. Our data reveal that Htt1a transcript levels are regulated by both METTL3 and the methylation status of Htt intron 1. They also show that m 6 A methylation in intron 1 depends on expanded CAG repeats. Our findings highlight a potential role for m 6 A in aberrant splicing of Htt mRNA., (© 2024. The Author(s).)

Activation-induced cytidine deaminase (AID, encoded by Aicda) plays a key role in somatic hypermutation and class switch recombination in germinal center B cells. However, off-target effects of AID are implicated in human leukemia and lymphoma. A mouse model of precursor B cell acute lymphoblastic leukemia driven by deletion of the related transcription factors PU.1 and Spi-B revealed C->T transition mutations compatible with being induced by AID. Therefore, we hypothesized that PU.1 negatively regulates Aicda during B cell development. Aicda mRNA transcript levels were increased in leukemia cells and bone marrow pre-B cells lacking PU.1 and/or Spi-B, relative to wild type cells. Using chromatin immunoprecipitation, PU.1 was found to interact with a negative regulatory region (R2-1) within the first intron of Aicda. CRISPR-Cas9-induced mutagenesis of R2-1 in cultured pre-B cells resulted in upregulation of Aicda in response to lipopolysaccharide stimulation. Mutation of the PU.1 interaction site and neighboring sequences resulted in reduced repressive ability of R2-1 in transient transfection analysis followed by luciferase assays. These results show that a PU.1-interacting intronic region negatively regulates Aicda transcription in developing B cells., Competing Interests: Declaration of Competing Interest The authors declare no competing interests, (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Background: This study aimed to investigate the relationships between eNOS T786C, G894T, intron 4 VNTR (4a/b) gene variations and prostate cancer development and progression., Materials and Methods: This study included 88 patients diagnosed with prostate cancer and 91 healthy controls. Polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP) methods were used to determine the genotype distributions of eNOS T786C, G894T, intron 4 VNTR (4a/b) gene variations., Results: In our study, the CC homozygous genotype of eNOS T786C gene variation was determined to be significantly higher in the prostate cancer patient group compared to the healthy control group (OR: 2.343, 95%Cl: 0.990-5.544, p = 0.026), while the CT heterozygous genotype was found to be significantly higher in the healthy control group compared to the prostate cancer patient group was found to be significantly higher (OR: 0.589, 95%Cl: 0.325-1.068, p = 0.041). In addition, while the TT homozygous genotype of the eNOS G894T gene variation was found to be significantly higher in the prostate cancer patient group compared to the healthy control group (OR: 9.068, 95%Cl: 4.396-18.777, p < 0.001), the GT heterozygous genotype was found to be significantly higher in the healthy control group compared to the prostate cancer patient group was determined significantly higher (OR: 0.227, 95%Cl: 0.121-0.427, p < 0.001). For eNOS (4VNTR (4a/b) - G894T) gene variations, aa-TT (p = 0.042) and bb-TT (p < 0.001) haplotype frequencies were significantly higher in the prostate cancer patient group, while aa-GT (p = 0.017), bb-GG (p = 0.049) and bb-GT (p < 0.001) haplotype frequencies were found to be significantly higher in the healthy control group. For eNOS (4VNTR (4a/b) - T786C) gene variations, the bb-CC haplotype frequency was determined to be significantly higher in the patient group (p = 0.049), while the bb-CT haplotype frequency was determined to be significantly higher in the control group (p = 0.008). For eNOS (T786C -G894T) gene variations, TT-TT (p < 0.001) and CC-TT (p = 0.025) haplotype frequencies were found to be significantly higher in the patient group. On the other hand, TT-GT (p = 0.002) and CT-GT (p < 0.001) haplotype frequencies were determined to be significantly higher in the control group. The aa genotype of the intron 4 VNTR (4a/b) gene variation was determined to be significantly higher at Gleason score ≥7 compared to Gleason score <7 (OR: 0.184, 95%Cl: 0.050-0.677, p = 0.005). PSA levels were determined significantly higher in patients with Gleason score 7 and above (p = 0.008). The risk of developing prostate cancer was found to be significantly higher in patients carrying the CC homozygous mutant genotype of the eNOS T786C gene variation (p = 0.024) and in patients carrying the TT homozygous genotype of the G894T gene variation (p = 0.021)., Conclusions: In our study, the CC homozygous genotype of the eNOS T786C gene variation was determined as a genetic risk factor for the development of prostate cancer, while the CT heterozygous genotype was determined as a protective factor against prostate cancer. For the eNOS G894T gene variation, the TT homozygous genotype was determined as a genetic risk factor for the development of prostate cancer, while the GT heterozygous genotype was determined as a protective factor against prostate cancer. Additionally, for eNOS (4VNTR (4a/b) - G894T) gene variations, aa-TT and bb-TT haplotypes have been identified as genetic risk factors for the development of prostate cancer, while aa-GT, bb-GG and bb-GT haplotypes have been identified as protective factors against the disease has been determined. For eNOS (4VNTR (4a/b) - T786C) gene variations, the bb-CC haplotype was determined as a genetic risk factor in the development of prostate cancer, while the bb-CT haplotype was determined as a protective factor against the disease. TT-TT and CC-TT haplotypes for eNOS (T786C -G894T) gene variations have been identified as genetic risk factors for the development of prostate cancer. In contrast, TT-GT and CT-GT haplotypes were found to be protective factors against the disease. The aa genotype of the intron 4 VNTR (4a/b) gene variation has also been identified as an important genetic risk factor in prostate cancer progression. Significantly increased PSA levels in patients with Gleason score 7 and above, and significantly increased PSA levels in patients carrying the CC and TT homozygous mutant genotype for T786C and G894T gene variations were determined as important risk factors. It is thought that the genetic biomarkers in our study may play a role as personalized therapeutic agents in slowing down the development of prostate cancer, increasing the effectiveness of treatment in prostate cancer, affecting the responses to drugs that regulate NO signaling, predetermining genetic predisposition to prostate cancer, and risk assessment in patients with prostate cancer., Competing Interests: Declaration of competing interest The authors declare that they have no conflict of interest., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Ever since their introduction a decade ago, stable introns, a type of noncoding (nc)RNAs, are found to be key players in different important cellular processes acting through regulation of gene expression and feedback loops to maintain cellular homeostasis. Despite being commonly regarded as useless byproducts, recent studies in yeast suggested that stable introns are essential for cell survivability under starvation. In Drosophila, we found that a stable intron, sisR-1, has a direct effect in regulating mitochondrial dynamics during short-term fasting and subsequently improved overall oocyte quality. We speculated that the beneficial effects implicated by sisR-1 is through the activation of mitohormesis, an interesting phenomenon in mitochondrial biology. Mitohormesis is suggested to improve health span and lifespan of cells and organisms, but the involvement of ncRNAs is not well-documented. Here, we discuss the potential role of sisR-1 and other ncRNAs in activating mitohormesis and the possible applications in improving cellular and organismal health., (© 2024 Wiley Periodicals LLC.)

Homing genetic elements are a form of selfish DNA that inserts into a specific target site in the genome and spreads through the population by a process of biased inheritance. Two well-known types of homing element, called inteins and homing introns, were discovered decades ago. In this review we describe WHO elements, a newly discovered type of homing element that constitutes a distinct third category but is rare, having been found only in a few yeast species so far. WHO elements are inferred to spread using the same molecular homing mechanism as inteins and introns: they encode a site-specific endonuclease that cleaves the genome at the target site, making a DNA break that is subsequently repaired by copying the element. For most WHO elements, the target site is in the glycolytic gene FBA1. WHO elements differ from inteins and homing introns in two fundamental ways: they do not interrupt their host gene (FBA1), and they occur in clusters. The clusters were formed by successive integrations of different WHO elements into the FBA1 locus, the result of an 'arms race' between the endonuclease and its target site. We also describe one family of WHO elements (WHO10) that is no longer specifically associated with the FBA1 locus and instead appears to have become transposable, inserting at random genomic sites in Torulaspora globosa with up to 26 copies per strain. The WHO family of elements is therefore at the borderline between homing genetic elements and transposable elements., Competing Interests: Declaration of Competing Interest The authors declare no conflict of interests., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Global warming poses a threat for crops, therefore, the identification of thermotolerance mechanisms is a priority. In plants, the core factors that regulate transcription under heat stress (HS) are well described and include several HS transcription factors (HSFs). Despite the relevance of alternative splicing in HS response and thermotolerance, the core regulators of HS-sensitive alternative splicing have not been identified. In tomato, alternative splicing of HSFA2 is important for acclimation to HS. Here, we show that several members of the serine/arginine-rich family of splicing factors (SRSFs) suppress HSFA2 intron splicing. Individual-nucleotide resolution UV cross-linking and immunoprecipitation (iCLIP) combined with RNA-Seq revealed that RS2Z35 and RS2Z36, which make up a plant-specific clade of SR proteins, not only regulate HSFA2 but approximately 50% of RNAs that undergo HS-sensitive alternative splicing, with preferential binding to purine-rich RNA motifs. Single and double CRISPR rs2z mutant lines show a dysregulation of splicing and exhibit lower basal and acquired thermotolerance compared to wild type plants. Our results suggest that RS2Z35 and RS2Z36 have a central role in mitigation of the negative effects of HS on RNA splicing homeostasis, and their emergence might have contributed to the increased capacity of plants to acclimate to high temperatures., (© The Author(s) 2024. Published by Oxford University Press on behalf of Nucleic Acids Research.)

We present SpliceTransformer (SpTransformer), a deep-learning framework that predicts tissue-specific RNA splicing alterations linked to human diseases based on genomic sequence. SpTransformer outperforms all previous methods on splicing prediction. Application to approximately 1.3 million genetic variants in the ClinVar database reveals that splicing alterations account for 60% of intronic and synonymous pathogenic mutations, and occur at different frequencies across tissue types. Importantly, tissue-specific splicing alterations match their clinical manifestations independent of gene expression variation. We validate the enrichment in three brain disease datasets involving over 164,000 individuals. Additionally, we identify single nucleotide variations that cause brain-specific splicing alterations, and find disease-associated genes harboring these single nucleotide variations with distinct expression patterns involved in diverse biological processes. Finally, SpTransformer analysis of whole exon sequencing data from blood samples of patients with diabetic nephropathy predicts kidney-specific RNA splicing alterations with 83% accuracy, demonstrating the potential to infer disease-causing tissue-specific splicing events. SpTransformer provides a powerful tool to guide biological and clinical interpretations of human diseases., (© 2024. The Author(s).)

Pathogenic variants in the MED13L gene are associated with the autosomal dominant MED13L syndrome, which is characterised by global developmental delay and cardiac malformations. We investigated two heterozygous MED13L variants located at the canonical donor splice site motif of exon 7: c.1009+1G>C and c.1009+5G>C. We report that in silico predictions suggested two possible outcomes: exon 7 skipping, resulting in loss of the phosphodegron motif essential for MED13L regulation, or activation of a cryptic donor site in intron 7, leading to intron retention. RNA analysis confirmed that both variants affected the exon 7 splice donor site, resulting in the retention of 73 bp of intron 7. This retention caused a frameshift and premature translation termination, consistent with haploinsufficiency. Our results highlight the importance of combining predictive and experimental approaches to understand the functional impact of splice site variants. These insights into the molecular consequences of MED13L variants provide a deeper understanding of the genetic basis of MED13L syndrome., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2024. No commercial re-use. See rights and permissions. Published by BMJ.)

Nuclear speckles are nuclear membraneless organelles in higher eukaryotic cells playing a vital role in gene expression. Using an in situ reverse transcription-based sequencing method, we study nuclear speckle-associated human transcripts. Our data indicate the existence of three gene groups whose transcripts demonstrate different speckle localization properties: stably enriched in nuclear speckles, transiently enriched in speckles at the pre-messenger RNA stage, and not enriched. We find that stably enriched transcripts contain inefficiently excised introns and that disruption of nuclear speckles specifically affects splicing of speckle-enriched transcripts. We further reveal RNA sequence features contributing to transcript speckle localization, indicating a tight interplay between transcript speckle enrichment, genome organization, and splicing efficiency. Collectively, our data highlight a role of nuclear speckles in both co- and posttranscriptional splicing regulation. Last, we show that genes with stably enriched transcripts are over-represented among genes with heat shock-up-regulated intron retention, hinting at a connection between speckle localization and cellular stress response.

RNA surveillance systems degrade aberrant RNAs that result from defective transcriptional termination, splicing, and polyadenylation. Defective RNAs in the nucleus are recognized by RNA-binding proteins and MTR4, and are degraded by the RNA exosome complex. Here, we detect aberrant RNAs in MTR4-depleted cells using long-read direct RNA sequencing and 3' sequencing. MTR4 destabilizes intronic polyadenylated transcripts generated by transcriptional read-through over one or more exons, termed 3' eXtended Transcripts (3XTs). MTR4 also associates with hnRNPK, which recognizes 3XTs with multiple exons. Moreover, the aberrant protein translated from KCTD13 3XT is a target of the hnRNPK-MTR4-RNA exosome pathway and forms aberrant condensates, which we name KCTD13 3eXtended Transcript-derived protein (KeXT) bodies. Our results suggest that RNA surveillance in human cells inhibits the formation of condensates of a defective polyadenylated transcript-derived protein., (© 2024. The Author(s).)

End-to-end RNA-sequencing methods that capture 5'-sequence content without cumbersome library manipulations are of great interest, particularly for analysis of long RNAs. While template-switching methods have been developed for RNA sequencing by distributive short-read RTs, such as the MMLV RTs used in SMART-Seq methods, they have not been adapted to leverage the power of ultraprocessive RTs, such as those derived from group II introns. To facilitate this transition, we dissected the individual processes that guide the enzymatic specificity and efficiency of the multistep template-switching reaction carried out by RTs, in this case, by MarathonRT. Remarkably, this is the first study of its kind, for any RT. First, we characterized the nucleotide specificity of nontemplated addition (NTA) reaction that occurs when the RT extends past the RNA 5'-terminus. We then evaluated the binding specificity of specialized template-switching oligonucleotides, optimizing their sequences and chemical properties to guide efficient template-switching reaction. Having dissected and optimized these individual steps, we then unified them into a procedure for performing RNA sequencing with MarathonRT enzymes, using a well-characterized RNA reference set. The resulting reads span a six-log range in transcript concentration and accurately represent the input RNA identities in both length and composition. We also performed RNA-seq from total human RNA and poly(A)-enriched RNA, with short- and long-read sequencing demonstrating that MarathonRT enhances the discovery of unseen RNA molecules by conventional RT. Altogether, we have generated a new pipeline for rapid, accurate sequencing of complex RNA libraries containing mixtures of long RNA transcripts., (© 2024 Guo et al.; Published by Cold Spring Harbor Laboratory Press for the RNA Society.)

The 18-exon human TKFC gene codes for dual-activity triokinase and FMN cyclase (TKFC) in an ORF, spanning from exon 2 to exon 18. In addition to TKFC-coding transcripts (classified as tkfc type by their intron-17 splice), databases contain evidence for alternative TKFC transcripts, but none of them has been expressed, studied, and reported in the literature. A novel full-ORF transcript was cloned from brain cDNA and sequenced (accession no. DQ344550). It results from an alternative 3' splice-site in intron 17. The cloned cDNA contains an ORF also spanning from exon 2 to exon 18 of the TKFC gene but with a 56-nt insertion between exons 17 and 18 (classified as tkfc&#95;ins56 type). This insertion introduces an in-frame stop, and the resulting ORF codes for a shorter TKFC variant, which, after expression, is enzymatically inactive. TKFC intron-17 splicing was found to be differentially expressed in human tissues. In a multiple-tissue northern blot using oligonucleotide probes, the liver showed a strong expression of the tkfc -like splice of intron 17, and the heart preferentially expressed the tkfc&#95;ins56 -like splice. Through a comparison to global expression data from massive-expression studies of human tissues, it was inferred that the intestine preferentially expresses TKFC transcripts that contain neither of those splices. An analysis of transcript levels quantified by RNA-Seq in the GTEX database revealed an exception to this picture due to the occurrence of a non-coding short transcript with a tkfc -like splice. Altogether, the results support the occurrence of potentially relevant transcript variants of the TKFC gene, differentially expressed in human tissues. (This work is dedicated in memoriam to Professor Antonio Sillero, 1938-2024, for his lifelong mentoring and his pioneering work on triokinase).

Most vertebrates have a rhodopsin gene with a five-exon structure for visual photoreception. By contrast, teleost fishes have an intron-less rhodopsin gene for visual photoreception and an intron-containing rhodopsin (exo-rhodopsin) gene for pineal photoreception. Here, our analysis of non-teleost and teleost fishes in various lineages of the Actinopterygii reveals that retroduplication after branching of the Polypteriformes produced the intron-less rhodopsin gene for visual photoreception, which converted the parental intron-containing rhodopsin gene into a pineal opsin in the common ancestor of the Teleostei. Additional analysis of a pineal opsin, pinopsin, shows that the pinopsin gene functions as a green-sensitive opsin together with the intron-containing rhodopsin gene for pineal photoreception in tarpon as an evolutionary intermediate state but is missing in other teleost fishes, probably because of the redundancy with the intron-containing rhodopsin gene. We propose an evolutionary scenario where unique retroduplication caused a "domino effect" on the functional diversification of teleost visual and pineal opsin genes., (© 2024. The Author(s).)

Background: Fabry disease is an X-linked lysosomal storage disease caused by the impairment of α-galactosidase A. The complex intronic haplotype (CIH) variants, located in promoter and intronic regulatory lesions, has been found in patients with classical forms of Fabry disease. We present a case of Fabry disease in female monozygotic twins exhibiting the CIH mutation and classical manifestations., Case Presentation: A 61-year-old woman with a history of stroke, carotid artery occlusion, hypertrophic cardiomyopathy, and chronic kidney disease was referred to the nephrology clinic for management of her chronic kidney disease. Her monozygotic twin sister also presented with hypertrophic cardiomyopathy, atrial flutter, carotid stenosis, and proteinuria. Clinical symptoms and a comprehensive family history strongly suggested the presence of Fabry disease. Genetic analysis revealed the presence of 5 variants within a complex intronic haplotype (CIH): c.-10 C > T, c.369 + 990 C > A, c.370 - 81&#95;370-77delCAGCC, c.640-16 A > G, and c.1000-22 C > T. We conducted a review of the patient's previous kidney biopsy findings, which demonstrated the presence of lamellated inclusion bodies in electron microscopy. Remarkably, both the monozygotic twin sister and her son exhibited the same genetic mutation. Enzyme replacement therapy was initiated for the patient. Her kidney function decreased throughout a thorough 2-year follow-up period, while there was a slight decrease in the left ventricular mass index., Conclusions: This is the first reported case of female monozygotic twins with the CIH variants representing cardiac, cerebrovascular, and renal manifestations suggestive of Fabry disease., (© 2024. The Author(s).)

We previously identified a homozygous Alu insertion variant (Alu&#95;Ins) in the 3'-untranslated region (3'-UTR) of SPINK1 as the cause of severe infantile isolated exocrine pancreatic insufficiency. Although we established that Alu&#95;Ins leads to the complete loss of SPINK1 mRNA expression, the precise mechanisms remained elusive. Here, we aimed to elucidate these mechanisms through a hypothesis-driven approach. Initially, we speculated that, owing to its particular location, Alu&#95;Ins could independently disrupt mRNA 3' end formation and/or affect other post-transcriptional processes such as nuclear export and translation. However, employing a 3'-UTR luciferase reporter assay, Alu&#95;Ins was found to result in only an ∼50% reduction in luciferase activity compared to wild type, which is insufficient to account for the severe pancreatic deficiency in the Alu&#95;Ins homozygote. We then postulated that double-stranded RNA (dsRNA) structures formed between Alu elements, an upstream mechanism regulating gene expression, might be responsible. Using RepeatMasker, we identified two Alu elements within SPINK1's third intron, both oriented oppositely to Alu&#95;Ins. Through RNAfold predictions and full-length gene expression assays, we investigated orientation-dependent interactions between these Alu repeats. We provide compelling evidence to link the detrimental effect of Alu&#95;Ins to extensive dsRNA structures formed between Alu&#95;Ins and pre-existing intronic Alu sequences, including the restoration of SPINK1 mRNA expression by aligning all three Alu elements in the same orientation. Given the widespread presence of Alu elements in the human genome and the potential for new Alu insertions at almost any locus, our findings have important implications for detecting and interpreting Alu insertions in disease genes., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2024 American Society of Human Genetics. Published by Elsevier Inc. All rights reserved.)

Group II introns are large catalytic RNAs, which reside mainly within genes encoding respiratory complex I (CI) subunits in angiosperms' mitochondria. Genetic and biochemical analyses led to the identification of many nuclear-encoded factors that facilitate the splicing of the degenerated organellar introns in plants. Here, we describe the analysis of the pentatricopeptide repeat (PPR) co-expressed intron splicing-1 (PCIS1) factor, which was identified in silico by its co-expression pattern with many PPR proteins. PCIS1 is well conserved in land plants but has no sequence similarity with any known protein motifs. PCIS1 mutant lines are arrested in embryogenesis and can be maintained by the temporal expression of the gene under the embryo-specific ABI3 promoter. The pABI3::PCIS1 mutant plants display low germination and stunted growth phenotypes. RNA-sequencing and quantitative RT-PCR analyses of wild-type and mutant plants indicated that PCIS1 is a novel splicing cofactor that is pivotal for the maturation of several nad transcripts in Arabidopsis mitochondria. These phenotypes are tightly associated with respiratory CI defects and altered plant growth. Our data further emphasize the key roles of nuclear-encoded cofactors that regulate the maturation and expression of mitochondrial transcripts for the biogenesis of the oxidative phosphorylation system, and hence for plant physiology. The discovery of novel splicing factors other than typical RNA-binding proteins suggests further complexity of splicing mechanisms in plant mitochondria., (© The Author(s) 2024. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists. All rights reserved. For commercial re-use, please contact reprints@oup.com for reprints and translation rights for reprints. All other permissions can be obtained through our RightsLink service via the Permissions link on the article page on our site–for further information please contact journals.permissions@oup.com.)

Alternative cleavage and polyadenylation within introns (intronic APA) generate shorter mRNA isoforms; however, their physiological significance remains elusive. In this study, we developed a comprehensive workflow to analyze intronic APA profiles using the mammalian target of rapamycin (mTOR)-regulated transcriptome as a model system. Our investigation revealed two contrasting effects within the transcriptome in response to fluctuations in cellular mTOR activity: an increase in intronic APA for a subset of genes and a decrease for another subset of genes. The application of this workflow to RNA-seq data from The Cancer Genome Atlas demonstrated that this dichotomous intronic APA pattern is a consistent feature in transcriptomes across both normal tissues and various cancer types. Notably, our analyses of protein length changes resulting from intronic APA events revealed two distinct phenomena in proteome programming: a loss of functional domains due to significant changes in protein length or minimal alterations in C-terminal protein sequences within unstructured regions. Focusing on conserved intronic APA events across 10 different cancer types highlighted the prevalence of the latter cases in cancer transcriptomes, whereas the former cases were relatively enriched in normal tissue transcriptomes. These observations suggest potential, yet distinct, roles for intronic APA events during pathogenic processes and emphasize the abundance of protein isoforms with similar lengths in the cancer proteome. Furthermore, our investigation into the isoform-specific functions of JMJD6 intronic APA events supported the hypothesis that alterations in unstructured C-terminal protein regions lead to functional differences. Collectively, our findings underscore intronic APA events as a discrete molecular signature present in both normal tissues and cancer transcriptomes, highlighting the contribution of APA to the multifaceted functionality of the cancer proteome., (© 2024. The Author(s).)

The removal of introns by the spliceosome is a key gene regulatory mechanism in eukaryotes, with the U1 snRNP subunit playing a crucial role in the early stages of splicing. Studies in metazoans show that the U1 snRNP also conducts splicing-independent functions, but the lack of genetic tools and knowledge about U1 snRNP-associated proteins have limited the study of such splicing-independent functions in plants. Here we describe an RNA-centric approach that identified more than 200 proteins associated with the Arabidopsis U1 snRNP and revealed a tight link to mRNA cleavage and polyadenylation factors. Interestingly, we found that the U1 snRNP protects mRNAs against premature cleavage and polyadenylation within introns-a mechanism known as telescripting in metazoans-while also influencing alternative polyadenylation site selection in 3'-UTRs. Overall, our work provides a comprehensive view of U1 snRNP interactors and reveals novel functions in regulating mRNA 3'-end processing in Arabidopsis, laying the groundwork for understanding non-canonical functions of plant U1 snRNPs., (© 2024. The Author(s).)

Intron retention (IR) constitutes a less explored form of alternative splicing, wherein introns are retained within mature mRNA transcripts. This investigation demonstrates that the cell division cycle (CDC)-like kinase 2 (CLK2) undergoes liquid-liquid phase separation (LLPS) within nuclear speckles in response to heat shock (HS). The formation of CLK2 condensates depends on the intrinsically disordered region (IDR) located within the N-terminal amino acids 1-148. Phosphorylation at residue T343 sustains CLK2 kinase activity and promotes overall autophosphorylation, which inhibits the LLPS activity of the IDR. These CLK2 condensates initiate the reorganization of nuclear speckles, transforming them into larger, rounded structures. Moreover, these condensates facilitate the recruitment of splicing factors into these compartments, restricting their access to mRNA for intron splicing and promoting the IR. The retained introns lead to the sequestration of transcripts within the nucleus. These findings extend to the realm of glioma stem cells (GSCs), where a physiological state mirroring HS stress inhibits T343 autophosphorylation, thereby inducing the formation of CLK2 condensates and subsequent IR. Notably, expressing the CLK2 condensates hampers the maintenance of GSCs. In conclusion, this research unveils a mechanism by which IR is propelled by CLK2 condensates, shedding light on its role in coping with cellular stress., (© 2024 The Author(s). Advanced Science published by Wiley‐VCH GmbH.)

Mounting evidence suggests a prominent role for alpha-synuclein (a-syn) in neuronal cell function. Alterations in the levels of cellular a-syn have been hypothesized to play a critical role in the development of Parkinson's disease (PD); however, mechanisms that control expression of the gene for a-syn (SNCA) in cis and trans as well as turnover of a-syn are not well understood. We analyzed whether methyl-CpG binding protein 2 (MeCP2), a protein that specifically binds methylated DNA, thus regulating transcription, binds at predicted binding sites in intron 1 of the SNCA gene and regulates a-syn protein expression. Chromatin immunoprecipitation (ChIP) and electrophoretic mobility-shift assays (EMSA) were used to confirm binding of MeCP2 to regulatory regions of SNCA. Site-specific methylation and introduction of localized mutations by CRISPR/Cas9 were used to investigate the binding properties of MeCP2 in human SK-N-SH neuroblastoma cells. The significance of MeCP2 for SNCA regulation was further investigated by overexpressing MeCP2 and mutated variants of MeCP2 in MeCP2 knockout cells. We found that methylation-dependent binding of MeCP2 at a restricted region of intron 1 of SNCA had a significant impact on the production of a-syn. A single nucleotide substitution near to CpG1 strongly increased the binding of MeCP2 to intron 1 of SNCA and decreased a-syn protein expression by 60%. In contrast, deletion of a single nucleotide closed to CpG2 led to reduced binding of MeCP2 and significantly increased a-syn levels. In accordance, knockout of MeCP2 in SK-N-SH cells resulted in a significant increase in a-syn production, demonstrating that SNCA is a genomic target for MeCP2 regulation. In addition, the expression of two mutated MeCP2 variants found in Rett syndrome (RTT) showed a loss of their ability to reduce a-syn expression. This study demonstrates that methylation of CpGs and binding of MeCP2 to intron 1 of the SNCA gene plays an important role in the control of a-syn expression. In addition, the changes in SNCA regulation found by expression of MeCP2 variants carrying mutations found in RTT patients may be of importance for the elucidation of a new molecular pathway in RTT, a rare neurological disorder caused by mutations in MECP2., (© 2024. The Author(s).)

Intronic polyadenylation (IPA) is an RNA 3' end processing event which has been reported to play important roles in cancer development. However, the comprehensive landscape of IPA events across various cancer types is lacking. Here, we apply IPAFinder to identify and quantify IPA events in 10,383 samples covering all 33 cancer types from The Cancer Genome Atlas (TCGA) project. We identify a total of 21,835 IPA events, almost half of which are ubiquitously expressed. We identify 2761 unique dynamically changed IPA events across cancer types. Furthermore, we observe 8855 non-redundant clinically relevant IPA events, which could potentially be used as prognostic indicators. Our analysis also reveals that dynamic IPA usage within cancer signaling pathways may affect drug response. Finally, we develop a user-friendly data portal, IPACancer Atlas (http://www.tingni-lab.com/Pancan&#95;IPA/), to search and explore IPAs in cancer., Competing Interests: Conflict of interest The authors declare no competing interests., (Copyright © 2024. Published by Elsevier Ltd.)

Horizontal gene transfer (HGT) is a major driving force in the evolution of prokaryotic and eukaryotic genomes. Despite recent advances in distribution and ecological importance, the extensive pattern, especially in seed plants, and post-transfer adaptation of HGT-acquired genes in land plants remain elusive. We systematically identified 1150 foreign genes in 522 land plant genomes that were likely acquired via at least 322 distinct transfers from nonplant donors and confirmed that recent HGT events were unevenly distributed between seedless and seed plants. HGT-acquired genes evolved to be more similar to native genes in terms of average intron length due to intron gains, and HGT-acquired genes containing introns exhibited higher expression levels than those lacking introns, suggesting that intron gains may be involved in the post-transfer adaptation of HGT in land plants. Functional validation of bacteria-derived gene GuaD in mosses and gymnosperms revealed that the invasion of foreign genes introduced a novel bypass of guanine degradation and resulted in the loss of native pathway genes in some gymnosperms, eventually shaping three major types of guanine metabolism in land plants. We conclude that HGT has played a critical role in land plant evolution., (© 2024 The Author(s). New Phytologist © 2024 New Phytologist Foundation.)

Background: Genetic variants in COL4A2 are less common than those of COL4A1 and their fetal clinical phenotype has not been well described to date. We present a fetus from China with an intronic variant in COL4A2 associated with a prenatal diagnosis of severe cerebral encephalomalacia and subdural hemorrhage., Methods: Whole exome sequencing (WES) was applied to screen potential genetic causes. Bioinformatic analysis was performed to predict the pathogenicity of the variant. In in vitro experiment, the minigene assays were performed to assess the variant's effect., Results: In this proband, we observed ventriculomegaly, subdural hemorrhage, and extensive encephalomalacia that initially suggested cerebral hypoxic-ischemic and/or hemorrhagic lesions. WES identified a de novo heterozygous variant c.549 + 5G > A in COL4A2 gene. This novel variant leads to the skipping of exon 8, which induces the loss of 24 native amino acids, resulting in a shortened COL4A2 protein (p.Pro161&#95;Gly184del)., Conclusion: Our study demonstrated that c.549 + 5G > A in COL4A2 gene is a disease-causing variant by aberrant splicing. This finding enriches the variant spectrum of COL4A2 gene, which not only improves the understanding of the fetal neurological disorders associated with hypoxic-ischemic and hemorrhagic lesions from a clinical perspective but also provides guidance on genetic diagnosis and counseling., (© 2024. The Author(s).)

Background: Hereditary spastic paraplegia (HSP) is a rare genetically heterogeneous neurodegenerative disorder. The most common type of HSP is caused by pathogenic variants in the SPAST gene. Various hypotheses regarding the pathogenic mechanisms of HSP-SPAST have been proposed. However, a single hypothesis may not be sufficient to explain HSP-SPAST., Objective: To determine the causative gene of autosomal dominant HSP-SPAST in a pure pedigree and to study its underlying pathogenic mechanism., Methods: A four-generation Chinese family was investigated. Genetic testing was performed for the causative gene, and a splice site variant was identified. In vivo and in vitro experiments were conducted separately. Western blotting and immunofluorescence were performed after transient transfection of cells with the wild-type (WT) or mutated plasmid. The developmental expression pattern of zebrafish spasts was assessed via whole-mount in situ hybridization. The designed guide RNA (gRNA) and an antisense oligo spast-MO were microinjected into Tg(hb9:GFP) zebrafish embryos, spinal cord motor neurons were observed, and a swimming behavioral analysis was conducted., Results: A novel heterozygous intron variant, c.1004 + 5G > A, was identified in a pure HSP-SPAST pedigree and shown to cosegregate with the disease phenotypes. This intron splice site variant skipped exon 6, causing a frameshift mutation that resulted in a premature termination codon. In vitro, the truncated protein was evenly distributed throughout the cytoplasm, formed filamentous accumulations around the nucleus, and colocalized with microtubules. Truncated proteins diffusing in the cytoplasm appeared denser. No abnormal microtubule structures were observed, and the expression levels of α-tubulin remained unchanged. In vivo, zebrafish larvae with this mutation displayed axon pathfinding defects, impaired outgrowth, and axon loss. Furthermore, spast-MO larvae exhibited unusual behavioral preferences and increased acceleration., Conclusion: The adverse effects of premature stop codon mutations in SPAST result in insufficient levels of functional protein, and the potential toxicity arising from the intracellular accumulation of spastin serves as a contributing factor to HSP-SPAST., (© 2024. The Author(s).)

Interpreting the clinical significance of putative splice-altering variants outside canonical splice sites remains difficult without time-intensive experimental studies. To address this, we introduce Parallel Splice Effect Sequencing (ParSE-seq), a multiplexed assay to quantify variant effects on RNA splicing. We first apply this technique to study hundreds of variants in the arrhythmia-associated gene SCN5A. Variants are studied in 'minigene' plasmids with molecular barcodes to allow pooled variant effect quantification. We perform experiments in two cell types, including disease-relevant induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs). The assay strongly separates known control variants from ClinVar, enabling quantitative calibration of the ParSE-seq assay. Using these evidence strengths and experimental data, we reclassify 29 of 34 variants with conflicting interpretations and 11 of 42 variants of uncertain significance. In addition to intronic variants, we show that many synonymous and missense variants disrupted RNA splicing. Two splice-altering variants in the assay also disrupt splicing and sodium current when introduced into iPSC-CMs by CRISPR-Cas9 editing. ParSE-seq provides high-throughput experimental data for RNA-splicing to support precision medicine efforts and can be readily adopted to study other loss-of-function genotype-phenotype relationships., (© 2024. The Author(s).)

A previous study using Thermostable Group II Intron Reverse Transcriptase sequencing (TGIRT-seq) found human plasma contains short (≤300 nt) structured full-length excised linear intron (FLEXI) RNAs with potential to serve as blood-based biomarkers. Here, TGIRT-seq identified >9,000 different FLEXI RNAs in human cell lines, including relatively abundant FLEXIs with cell-type-specific expression patterns. Analysis of public CLIP-seq datasets identified 126 RNA-binding proteins (RBPs) that have binding sites within the region corresponding to the FLEXI or overlapping FLEXI splice sites in pre-mRNAs, including 53 RBPs with binding sites for ≥30 different FLEXIs. These included splicing factors, transcription factors, a chromatin remodeling protein, cellular growth regulators, and proteins with cytoplasmic functions. Analysis of ENCODE datasets identified subsets of these RBPs whose knockdown impacted FLEXI host gene mRNA levels or proximate alternative splicing, indicating functional interactions. Hierarchical clustering identified six subsets of RBPs whose FLEXI binding sites were co-enriched in six subsets of functionally related host genes: AGO1-4 and DICER, including but not limited to agotrons or mirtron pre-miRNAs; DKC1, NOLC1, SMNDC1, and AATF (Apoptosis Antagonizing Transcription Factor), including but not limited to snoRNA-encoding FLEXIs; two subsets of alternative splicing factors; and two subsets that included RBPs with cytoplasmic functions (e.g., LARP4, PABPC4, METAP2, and ZNF622) together with regulatory proteins. Cell fractionation experiments showed cytoplasmic enrichment of FLEXI RNAs with binding sites for RBPs with cytoplasmic functions. The subsets of host genes encoding FLEXIs with binding sites for different subsets of RBPs were co-enriched with non-FLEXI other short and long introns with binding sites for the same RBPs, suggesting overarching mechanisms for coordinately regulating expression of functionally related genes. Our findings identify FLEXIs as a previously unrecognized large class of cellular RNAs and provide a comprehensive roadmap for further analyzing their biological functions and the relationship of their RBPs to cellular regulatory mechanisms., Competing Interests: I have read the journal’s policy and the authors of this manuscript have the following competing interests: AML is an inventor on patents owned by the University of Texas at Austin for TGIRT enzymes and other stabilized reverse transcriptase fusion proteins and methods for non-retroviral reverse transcriptase template switching. AML, JY, and HX are inventors on a patent application filed by the University of Texas for the use of FLEXIs and other intron RNAs as biomarkers., (Copyright: © 2024 Yao et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

Background: SINE-VNTR-Alu (SVA) retrotransposons move from one genomic location to another in a 'copy-and-paste' manner. They continue to move actively and cause monogenic diseases through various mechanisms. Currently, disease-causing SVA retrotransposons are classified into human-specific young SVA&#95;E or SVA&#95;F subfamilies. In this study, we identified an evolutionarily old SVA&#95;D retrotransposon as a novel cause of occipital horn syndrome (OHS). OHS is an X-linked, copper metabolism disorder caused by dysfunction of the copper transporter, ATP7A., Methods: We investigated a 16-year-old boy with OHS whose pathogenic variant could not be detected via routine molecular genetic analyses., Results: A 2.8 kb insertion was detected deep within the intron of the patient's ATP7A gene. This insertion caused aberrant mRNA splicing activated by a new donor splice site located within it. Long-read circular consensus sequencing enabled us to accurately read the entire insertion sequence, which contained highly repetitive and GC-rich segments. Consequently, the insertion was identified as an SVA&#95;D retrotransposon. Antisense oligonucleotides (AOs) targeting the new splice site restored the expression of normal transcripts and functional ATP7A proteins. AO treatment alleviated excessive accumulation of copper in patient fibroblasts in a dose-dependent manner. Pedigree analysis revealed that the retrotransposon had moved into the OHS-causing position two generations ago., Conclusion: This is the first report of a human monogenic disease caused by the SVA&#95;D retrotransposon. The fact that the evolutionarily old SVA&#95;D is still actively transposed, leading to increased copy numbers may make a notable impact on rare genetic disease research., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2024. No commercial re-use. See rights and permissions. Published by BMJ.)

DNA splice junction classification is a crucial job in computational biology. The challenge is to predict the junction type (IE, EI, or N) from a given DNA sequence. Predicting junction type is crucial for understanding gene expression patterns, disease causes, splicing regulation, and gene structure. The location of the regions where exons are joined, and introns are removed during RNA splicing is very difficult to determine because no universal rule guides this process. This study presents a two-layer hybrid approach inspired by ensemble learning to overcome this challenge. The first layer applies the grey wolf optimizer (GWO) for feature selection. GWO's exploration ability allows it to efficiently search a vast feature space, while its exploitation ability refines promising areas, thus leading to a more reliable feature selection. The selected features are then fed into the second layer, which employs a classification model trained on the retrieved features. Using cross-validation, the proposed method divides the DNA splice junction dataset into training and test sets, allowing for a thorough examination of the classifier's generalization ability. The ensemble model is trained on various partitions of the training set and tested on the remaining held-out fold. This process is performed for each fold, comprehensively evaluating the classifier's performance. We tested our method using the StatLog DNA dataset. Compared to various machine learning models for DNA splice junction prediction, the proposed GWO+SVM ensemble method achieved an accuracy of 96%. This finding suggests that the proposed ensemble hybrid approach is promising for DNA splice junction classification. The implementation code for the proposed approach is available at https://github.com/EFHamouda/DNA-splice-junction-prediction., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2024 Hamouda, Tarek. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

Autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED) is a life-threatening monogenic autoimmune disorder primarily caused by biallelic deleterious variants in the autoimmune regulator ( AIRE ) gene. We prospectively evaluated 104 patients with clinically diagnosed APECED syndrome and identified 17 patients (16%) from 14 kindreds lacking biallelic AIRE variants in exons or flanking intronic regions; 15 had Puerto Rican ancestry. Through whole-genome sequencing, we identified a deep intronic AIRE variant (c.1504-818 G>A) cosegregating with the disease in all 17 patients. We developed a culture system of AIRE -expressing primary patient monocyte-derived dendritic cells and demonstrated that c.1504-818 G>A creates a cryptic splice site and activates inclusion of a 109-base pair frame-shifting pseudoexon. We also found low-level AIRE expression in patient-derived lymphoblastoid cell lines (LCLs) and confirmed pseudoexon inclusion in independent extrathymic AIRE -expressing cell lines. Through protein modeling and transcriptomic analyses of AIRE -transfected human embryonic kidney 293 and thymic epithelial cell 4D6 cells, we showed that this variant alters the carboxyl terminus of the AIRE protein, abrogating its function. Last, we developed an antisense oligonucleotide (ASO) that reversed pseudoexon inclusion and restored the normal AIRE transcript sequence in LCLs. Thus, our findings revealed c.1504-818 G>A as a founder APECED-causing AIRE variant in the Puerto Rican population and uncovered pseudoexon inclusion as an ASO-reversible genetic mechanism underlying APECED.

Rationale : Circular RNA (circRNA) therapeutics hold great promise as an iteration strategy in messenger RNA (mRNA) therapeutics due to their inherent stability and durable protein translation capability. Nevertheless, the efficiency of RNA circularization remains a significant constraint, particularly in establishing large-scale manufacturing processes for producing highly purified circRNAs. Hence, it is imperative to develop a universal and more efficient RNA circularization system when considering synthetic circRNAs as therapeutic agents with prospective clinical applications. Methods: We initially developed a chimeric RNA circularization system based on the original permuted intron-exon (PIE) and subsequently established a high-performance liquid chromatography (HPLC) method to obtain highly purified circRNAs. We then evaluated their translational ability and immunogenicity. The circRNAs expressing human papillomavirus (HPV) E7 peptide (43-62aa) and dimerized receptor binding domain (dRBD) from SARS-CoV-2 were encapsulated within lipid nanoparticles (LNPs) as vaccines, followed by an assessment of the in vivo efficacy through determination of antigen-specific T and B cell responses, respectively. Results: We have successfully developed a universal chimeric permuted intron-exon system (CPIE) through engineering of group I self-splicing introns derived from Anabaena pre-tRNA Leu or T4 phage thymidylate (Td) synthase gene. Within CPIE, we have effectively enhanced RNA circularization efficiency. By utilizing size exclusion chromatography, circRNAs were effectively separated, which exhibit low immunogenicity and sustained potent protein expression property. In vivo data demonstrate that the constructed circRNA vaccines can elicit robust immune activation (B cell and/or T cell responses) against tumor or SARS-CoV-2 and its variants in mouse models. Conclusions: Overall, we provide an efficient and universal system to synthesize circRNA in vitro , which has extensive application prospect for circRNA therapeutics., Competing Interests: Competing Interests: The authors have declared that no competing interest exists., (© The author(s).)

The Mycobacterium tuberculosis variant bovis ( M. bovis ) is a highly pathogenic environmental microorganism that causes bovine tuberculosis (bTB), a significant zoonotic disease. Currently, "test and culling" is the primary measure for controlling bTB, but it has been proven to be inadequate in animals due to their high susceptibility to the pathogen. Selective breeding for increased host resistance to bTB to reduce its prevalence is feasible. In this study, we found a vital host-dependent factor, RBMX2 , that can potentially promote M. bovis infection. By knocking RBMX2 out, we investigated its function during M. bovis infection. Through transcriptome sequencing and alternative splicing transcriptome sequencing, we concluded that after M. bovis infection, embryo bovine lung (EBL) cells were significantly enriched in RNA splicing associated with apoptosis compared with wild-type EBL cells. Through protein/molecular docking, molecular dynamics simulations, and real-time quantitative PCR, we demonstrated that RBMX2 promotes the apoptosis of epithelial cells by upregulating and binding to apoptotic peptidase activating factor 1 (APAF-1), resulting in the alternative splicing of APAF-1 as a retention intron. To our knowledge, this is the first report of M. bovis affecting host epithelial cell apoptosis by hijacking RBMX2 to promote the intron splicing of downstream APAF-1. These findings may represent a significant contribution to the development of novel TB prevention and control strategies., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Wang, Jiang, Yang, Xu, Khalid, Iftakhar, Peng, Lu, Zhang, Bermudez, Guo and Chen.)

Multiple acyl-CoA dehydrogenase deficiency (MADD) is a rare inborn error of metabolism affecting fatty acid and amino acid oxidation with an incidence of 1 in 200,000 live births. MADD has three clinical phenotypes: severe neonatal-onset with or without congenital anomalies, and a milder late-onset form. Clinical diagnosis is supported by urinary organic acid and blood acylcarnitine analysis using tandem mass spectrometry in newborn screening programs. MADD is an autosomal recessive trait caused by biallelic mutations in the ETFA , ETFB , and ETFDH genes encoding the alpha and beta subunits of the electron transfer flavoprotein (ETF) and ETF-coenzyme Q oxidoreductase enzymes. Despite significant advancements in sequencing techniques, many patients remain undiagnosed, impacting their access to clinical care and genetic counseling. In this report, we achieved a definitive molecular diagnosis in a newborn by combining whole-genome sequencing (WGS) with RNA sequencing (RNA-seq). Whole-exome sequencing and next-generation gene panels fail to detect variants, possibly affecting splicing, in deep intronic regions. Here, we report a unique deep intronic mutation in intron 1 of the ETFDH gene, c.35-959A>G, in a patient with early-onset lethal MADD, resulting in pseudo-exon inclusion. The identified variant is the third mutation reported in this region, highlighting ETFDH intron 1 vulnerability. It cannot be excluded that these intronic sequence features may be more common in other genes than is currently believed. This study highlights the importance of incorporating RNA analysis into genome-wide testing to reveal the functional consequences of intronic mutations.

Heat stress (HS) poses a significant challenge to plant survival, necessitating sophisticated molecular mechanisms to maintain cellular homeostasis. Here, we identify SICKLE (SIC) as a key modulator of HS responses in Arabidopsis (Arabidopsis thaliana). SIC is required for the sequestration of RNA DEBRANCHING ENZYME 1 (DBR1), a rate-limiting enzyme of lariat intronic RNA (lariRNA) decay, into stress granules (SGs). The sequestration of DBR1 by SIC enhances the accumulation of lariRNAs, branched circular RNAs derived from excised introns during pre-mRNA splicing, which in turn promote the transcription of their parental genes. Our findings further demonstrate that SIC-mediated DBR1 sequestration in SGs is crucial for plant HS tolerance, as deletion of the N-terminus of SIC (SIC 1-244 ) impairs DBR1 sequestration and compromises plant response to HS. Overall, our study unveils a mechanism of transcriptional regulation in the HS response, where lariRNAs are enriched through DBR1 sequestration, ultimately promoting the transcription of heat stress tolerance genes., (© 2024. The Author(s).)

Plants possess a robust and sophisticated innate immune system against pathogens and must balance growth with rapid pathogen detection and defense. The intracellular receptors with nucleotide-binding leucine-rich repeat (NLR) motifs recognize pathogen-derived effector proteins and thereby trigger the immune response. The expression of genes encoding NLR receptors is precisely controlled in multifaceted ways. The alternative splicing (AS) of introns in response to infection is recurrently observed but poorly understood. Here we report that the potato (Solanum tuberosum) NLR gene RB undergoes AS of its intron, resulting in 2 transcriptional isoforms, which coordinately regulate plant immunity and growth homeostasis. During normal growth, RB predominantly exists as an intron-retained isoform RB&#95;IR, encoding a truncated protein containing only the N-terminus of the NLR. Upon late blight infection, the pathogen induces intron splicing of RB, increasing the abundance of RB&#95;CDS, which encodes a full-length and active R protein. By deploying the RB splicing isoforms fused with a luciferase reporter system, we identified IPI-O1 (also known as Avrblb1), the RB cognate effector, as a facilitator of RB AS. IPI-O1 directly interacts with potato splicing factor StCWC15, resulting in altered localization of StCWC15 from the nucleoplasm to the nucleolus and nuclear speckles. Mutations in IPI-O1 that eliminate StCWC15 binding also disrupt StCWC15 re-localization and RB intron splicing. Thus, our study reveals that StCWC15 serves as a surveillance facilitator that senses the pathogen-secreted effector and regulates the trade-off between RB-mediated plant immunity and growth, expanding our understanding of molecular plant-microbe interactions., Competing Interests: Conflict of interest statement. None declared., (© The Author(s) 2024. Published by Oxford University Press on behalf of American Society of Plant Biologists. All rights reserved. For commercial re-use, please contact reprints@oup.com for reprints and translation rights for reprints. All other permissions can be obtained through our RightsLink service via the Permissions link on the article page on our site—for further information please contact journals.permissions@oup.com. Elements of this work were written by employees of the US Government.)

Competing Interests: Competing interests statement:The authors declare no competing interest.

Alternative splicing (AS) in human genes is widely viewed as a mechanism for enhancing proteomic diversity. AS can also impact gene expression levels without increasing protein diversity by producing 'unproductive' transcripts that are targeted for rapid degradation by nonsense-mediated decay (NMD). However, the relative importance of this regulatory mechanism remains underexplored. To better understand the impact of AS-NMD relative to other regulatory mechanisms, we analyzed population-scale genomic data across eight molecular assays, covering various stages from transcription to cytoplasmic decay. We report threefold more unproductive splicing compared with prior estimates using steady-state RNA. This unproductive splicing compounds across multi-intronic genes, resulting in 15% of transcript molecules from protein-coding genes being unproductive. Leveraging genetic variation across cell lines, we find that GWAS trait-associated loci explained by AS are as often associated with NMD-induced expression level differences as with differences in protein isoform usage. Our findings suggest that much of the impact of AS is mediated by NMD-induced changes in gene expression rather than diversification of the proteome., (© 2024. The Author(s).)

RNA splicing is a dynamic molecular process in response to environmental stimuli and is strictly regulated by the spliceosome. Sm proteins, constituents of the spliceosome, are key components that mediate splicing reactions; however, their potential role in hepatocellular carcinoma (HCC) is poorly understood. In the study, SNRPD2 (PD2) is found to be the most highly upregulated Sm protein in HCC and to act as an oncogene. PD2 modulates DDX39A intron retention together with HNRNPL to sustain the DDX39A short variant (39A&#95;S) expression. Mechanistically, 39A&#95;S can mediate MYC mRNA nuclear export to maintain high MYC protein expression, while MYC in turn potentiates PD2 transcription. Importantly, digitoxin can directly interact with PD2 and has a notable cancer-suppressive effect on HCC. The study reveals a novel mechanism by which DDX39A senses oncogenic MYC signaling and undergoes splicing via PD2 to form a positive feedback loop in HCC, which can be targeted by digitoxin., (© 2024 The Author(s). Advanced Science published by Wiley‐VCH GmbH.)

SF3B1 is the most recurrently mutated RNA splicing gene in cancer. However, research of its pathogenic role has been hindered by a lack of disease-relevant cell line models. Here, our study compared four genome engineering platforms to establish SF3B1 mutant cell lines: CRISPR-Cas9 editing, AAV homology-directed repair editing, base editing (ABEmax, ABE8e), and prime editing (PE2, PE3, PE5max). We showed that prime editing via PE5max achieved the most efficient SF3B1 K700E editing across a wide range of cell lines. Our approach was further refined by coupling prime editing with a fluorescent reporter that leverages a SF3B1 mutation-responsive synthetic intron to mark successfully edited cells. By applying this approach, called prime editing coupled intron-assisted selection (PRECIS), we introduced the K700E hotspot mutation into two chronic lymphocytic leukemia cell lines, HG-3 and MEC-1. We demonstrated that our PRECIS-engineered cells faithfully recapitulate known mutant SF3B1 phenotypes, including altered splicing, copy number variations, and cell-growth defect. Moreover, we discovered that the SF3B1 mutation can cause the loss of Y chromosome in chronic lymphocytic leukemia. Our results showcase that PRECIS is an efficient and generalizable method for engineering genetically faithful SF3B1 mutant models. Our approach provides new insights on the role of SF3B1 mutation in cancer and enables the generation of SF3B1 mutant cell lines in relevant cellular context., Significance: This study developed an approach that can reliably and efficiently engineer SF3B1 mutation into different cellular contexts, thereby revealing novel roles of SF3B1 mutation in driving aberrant splicing, clonal evolution, and genome instability., (©2024 The Authors; Published by the American Association for Cancer Research.)

The protein levels of chloroplast photosynthetic genes and genes related to the chloroplast genetic apparatus vary to adapt to different conditions. However, the underlying mechanisms governing these variations remain unclear. The chloroplast intron Maturase K is encoded within the trnK intron and has been suggested to be required for splicing several group IIA introns, including the trnK intron. In this study, we used RNA immunoprecipitation followed by high-throughput sequencing (RIP-Seq) to identify MatK's preference for binding to group IIA intron domains I and VI within target transcripts. Importantly, these domains are crucial for splice site selection, and we discovered alternative 5'-splice sites in three MatK target introns. The resulting alternative trnK lariat structure showed increased accumulation during heat acclimation. The cognate codon of tRNA-K(UUU) is highly enriched in mRNAs encoding ribosomal proteins and a trnK-matK over-expressor exhibited elevated levels of the spliced tRNA-K(UUU). Ribosome profiling analysis of the overexpressor revealed a significant up-shift in the translation of ribosomal proteins compared to photosynthetic genes. Our findings suggest the existence of a novel regulatory mechanism linked to the abundance of tRNA-K(UUU), enabling the differential expression of functional chloroplast gene groups., (© 2024 The Author(s). The Plant Journal published by Society for Experimental Biology and John Wiley & Sons Ltd.)

Type IV collagen is an integral component of basement membranes. Mutations in COL4A1, one of the key genes encoding Type IV collagen, can result in a variety of diseases. It is clear that a significant proportion of mutations that affect splicing can cause disease directly or contribute to the susceptibility or severity of disease. Here, we analyzed exonic mutations and intronic mutations described in the COL4A1 gene using bioinformatics programs and identified candidate mutations that may alter the normal splicing pattern through a minigene system. We identified seven variants that induce splicing alterations by disrupting normal splice sites, creating new ones, or altering splice regulatory elements. These mutations are predicted to impact protein function. Our results help in the correct molecular characterization of variants in COL4A1 and may help develop more personalized treatment options., (© 2024 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Spotted knifejaw (Oplegnathus punctatus), one of the most valuable mariculture species, grows with significant sexual dimorphism, with males growing significantly faster than females. O. punctatus not only has excellent growth characteristics and high food value, but also shows high economic value in aquaculture, which has become a hotspot in the field of aquaculture. The current insufficiency of sex marker identification in O. punctatus restricts the process of its unisexual breeding. Rapid identification of sex will help to study the mechanisms of sex determination and accelerate the development of sex-controlled breeding. With the completion of the sequencing of the male and female genomes of O. punctatus, the efficient and precise development of genetic sex markers has been made possible. In this study, we used genome-wide information combined with molecular biology techniques from marker sequences to further establish a rapid method for DNA insertion variant detection in the intron of O. punctatus erc2 gene, which can be used to rapidly, accurately, and efficiently identify whether DNA insertion occurs in the intron of O. punctatus erc2 gene to be detected, and to identify the sex of O. punctatus to be detected. It could also be distinguished by agarose gel electrophoresis, which would shorten the time for accurate identification and improves the detection efficiency. Homozygous comparison of male and female individuals showed that the length of the DNA fragment of the erc2 gene was 239 bp on chromosome X 1 and 1173 bp on chromosome Y. It can therefore be inferred that a 934 bp insertion fragment exists on the Y chromosome. The PCR amplification results showed that two DNA fragments of 1173 bp and 239 bp could be amplified in male O. punctatus, and the 1173 bp fragment was a marker fragment specific to the variant intron erc2 gene, while only a single DNA fragment of 239 bp was amplified in female O. punctatus. It has important significance and application value in the study of neurotransmitter transmission and environmental adaptability of female and male fish based on erc2 gene, as well as the identification of male and female sex, the preparation of high male fry, and family breeding., (© 2024. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Spotted knifejaw (Oplegnathus punctatus) is a significant marine fish species that exhibits pronounced sexual dimorphism, with males generally exhibiting greater weight and growth rates than females. Therefore, the farming of O. punctatus with a high proportion of males is beneficial for improving the quality and efficiency of the O. punctatus aquaculture industry. Furthermore, the development of a rapid technique in sexing O. punctatus fry will facilitate the selection and breeding of superior male varieties of O. punctatus. In this study, genome-wide scanning, comparative genomics, and structural variation analysis methods were employed to identify and extract the homologous region of the inter-alpha-trypsin inhibitor heavy chain 4 (itih4b) gene on the X and Y chromosomes from the complete genome sequence of O. punctatus. This analysis revealed the presence of a large segment of DNA insertion markers on the Y chromosome in the region. Itih4b plays an important role in the mechanisms that regulate inflammatory and immune responses in multicellular organisms. The method described here involved the design of a pair of primers to amplify two bands of 532 bp and 333 bp in males (individuals with DNA insertion variants in the intron of the itih4b gene). In females (individuals without DNA insertion), only one band of 333 bp could be distinguished by agarose gel electrophoresis. This method shortened the time required to accurately characterize intronic DNA insertion variants and genetic sexes in O. punctatus, thereby improving detection efficiency. This study has significant value for the large-scale breeding of O. punctatus all-male seedlings and provides a reference point for the study of intron variation regulation and RNA shearing in the itih4b gene., (© 2024. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

In vitro circular RNA (circRNA) preparation methods have been gaining a lot of attention recently as several reports suggest that circRNAs are more stable, with better performances in cells and in vivo, than linear RNAs in various biomedical applications. Self-splicing ribozymes are considered a major in vitro circRNA generation method for biomedical applications due to their simplicity and efficiency in the circularization of the gene of interest. This review summarizes, updates, and discusses the recently developed self-circularization methods based on the self-splicing ribozyme, such as group I and II intron ribozymes, and the pros and cons of each method in preparing circRNA in vitro.

The Greying with age phenotype in horses involves loss of hair pigmentation whereas skin pigmentation is not reduced, and a predisposition to melanoma. The causal mutation was initially reported as a duplication of a 4.6 kb intronic sequence in Syntaxin 17. The speed of greying varies considerably among Grey horses. Here we demonstrate the presence of two different Grey alleles, G2 carrying two tandem copies of the duplicated sequence and G3 carrying three. The latter is by far the most common allele, probably due to strong selection for the striking white phenotype. Our results reveal a remarkable dosage effect where the G3 allele is associated with fast greying and high incidence of melanoma whereas G2 is associated with slow greying and low incidence of melanoma. The copy number expansion transforms a weak enhancer to a strong melanocyte-specific enhancer that underlies hair greying (G2 and G3) and a drastically elevated risk of melanoma (G3 only). Our direct pedigree-based observation of the origin of a G2 allele from a G3 allele by copy number contraction demonstrates the dynamic evolution of this locus and provides the ultimate evidence for causality of the copy number variation of the 4.6 kb intronic sequence., (© 2024. The Author(s).)