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Human neuromuscular organoids (NMOs) derived from induced pluripotent stem cells (hiPSCs) hold a great potential to study (dys)functional human skeletal muscle (SkM) in vitro. The three-dimensional (3D) self-assembly of NMOs leads to the generation of spheroids, whose 3D organization cannot be controlled. Indeed, proper development, maturation and function of the innervated SkM require a well-defined multiscale 3D organization of the cells in a tissue-specific extracellular matrix (ECM) context. We hypothesized that extracellular structural imprinting along with hiPSC small-molecule-based differentiation could provide self-assembly guidance driving NMO morphogenesis and promoting the maturation and function of the human neuronal-coupled SkM in vitro models. We found that SkM ECM, provided as decellularized skeletal muscle, is able to reproducibly guide the morphogenesis of differentiating hiPSC toward multiscale structured tissue-like NMOs (t-NMOs). T-NMOs show contractile activity and possess functional neuromuscular junctions (NMJs), with mature neuromuscular system upon 30 days of hiPSC differentiation. We found that t-NMO could mimic altered muscle contraction upon administration of neurotoxins that act at NMJ level. Finally, we used hiPSCs derived from patients affected by Duchenne Muscular Dystrophy (DMD) to produce DMD t-NMOs that, upon neuronal stimulation, were able to mimic the altered SkM contractility and calcium dynamics typical of the disease. Altogether, our data confirm the ability of t-NMO platform to model in vitro human neuromuscular system (patho)physiology.

The high mutation rate of SARS-CoV-2 leads to emergence of several variants, some of which are resistant to vaccines and drugs targeting viral elements. Targeting host dependency factors – cell proteins required for viral replication - would help avoid resistance. However, whether different SARS-CoV-2 variants induce conserved cell responses and exploit the same core host factors is still unclear.We compared three variants of concern and observed that the host transcriptional response was conserved, differing only in kinetics and magnitude. By CRISPR screening we identified the host genes required for infection by each variant: most of the identified genes were shared by multiple variants, both in lung and colon cells. We validated our hits with small molecules and repurposed FDA-approved drugs. All drugs were highly effective against all tested variants, including delta and omicron, new variants that emerged during the study. Mechanistically, we identified ROS production as a pivotal step in early virus propagation. Antioxidant drugs, such as N-acetyl cysteine (NAC), were effective against all variants both in human lung cells, and in a humanised mouse model. Our study supports the use of available antioxidant drugs, such as NAC, as a general and effective anti-COVID-19 approach.

Pluripotency is the potential of a single cell to give rise to all embryonic lineages and first emerges in the naïve epiblast of the preimplantation embryo. Upon implantation, epiblast cells transit to a formative phase, which is preparatory for their differentiation into all somatic lineages and primordial germ cells (PGCs). Murine naïve embryonic stem cells (ESCs) recapitulate the molecular and functional properties of the naïve epiblast, including the capacity to acquire a formative state and differentiate. However, the transition to the formative state, and its functional relevance, is still heavily investigated. Here we observed that Esrrb, a pivotal naïve pluripotency factor, is both required and sufficient to activate formative genes. In naïve cells ESRRB occupies both naïve and formative gene loci. During the formative transition, however, ESRRB binding becomes consolidated on formative genes. Subsequently, ESRRB occupancy is mostly lost, and the formative transcriptional program is inactivated. Functionally, genetic inactivation of Esrrb leads to impaired PGC specification, spontaneous expression of mesendoderm and trophectoderm markers, and inability to generate Formative Stem (FS) cells. Moreover, the 3D organisation in a polarised epithelium with a central lumen, as observed in the formative epiblast, is impaired in the absence of Esrrb. Thus, Esrrb is critical for activating the formative transition and consequently for executing timely and unbiased multilineage differentiation and self-organisation of murine pluripotent cells.

Retromer controls cellular homeostasis through regulating integral membrane protein sorting and transport and by controlling late-stage maturation of the endo-lysosomal network. Retromer dysfunction, which is linked to neurodegenerative disorders including Parkinson’s and Alzheimer’s diseases, manifests in complex cellular phenotypes, though the precise nature of this dysfunction, and its relation to neurodegeneration, remain unclear. Here, we perform the first integrated multiomics approach to provide precise insight into the impact of Retromer dysfunction on endo-lysosomal health and homeostasis within a human neuroglioma cell model. We quantify profound changes to the lysosomal proteome, indicative of broad lysosomal dysfunction and inefficient autophagic lysosome reformation, coupled with a reconfigured cell surface proteome and secretome reflective of increased lysosomal exocytosis. Through this global proteomic approach and parallel transcriptomic analysis, we provide an unprecedented integrated view of Retromer function in regulating lysosomal homeostasis and emphasise its role in neuroprotection.

Cerebral cavernous malformations (CCM) are capillary malformations affecting the central nervous system and commonly present with headaches, epilepsy and stroke. Treatment of CCM is symptomatic, and its prevention is limited. CCM are often sporadic but sometimes may be multifocal and/or affect multiple family members. Heterozygous pathogenic variants in PDCD10 cause the rarest and apparently most severe genetic variant of familial CCM. We carried out an RNA-Seq and a Q-PCR validation analysis in Pdcd10-silenced and wild-type mouse endothelial cells in order to better elucidate CCM molecular pathogenesis. Ninety-four differentially expressed genes presented an FDR-corrected p-value < 0.05. A functionally clustered dendrogram showed that differentially expressed genes cluster in cell proliferation, oxidative stress, vascular processes and immune response gene-ontology functions. Among differentially expressed genes, the major cluster fell in signaling related to inflammation and pathogen recognition, including HIF1α and Nos2 signaling and immune regulation. Validation analysis performed on wild-type, Pdcd10-null and Pdcd10-null reconstituted cell lines was consistent with RNA-Seq data. This work confirmed previous mouse transcriptomic data in endothelial cells, which are recognized as a critical tissue for CCM formation and expands the potential molecular signatures of PDCD10-related familial CCM to alterations in inflammation and pathogen recognition pathways.

Besides the timely detection of different SARS-CoV-2 variants through surveillance systems, functional and modelling studies are essential to better inform public health response and preparedness. Here, the knowledge available so far on SARS-CoV-2 variants is discussed from different perspectives, in order to highlight the relevance of a multidisciplinary approach in countering the threat posed by this insidious virus.

BACKGROUND: Pregnant women have been identified as a potentially at-risk group concerning COVID-19 infection, but little is known regarding the susceptibility of the fetus to infection. Co-expression of ACE2 and TMPRSS2 has been identified as a prerequisite for infection, and expression across different tissues is known to vary between children and adults. However, the expression of these proteins in the fetus is unknown. METHODS: We performed a retrospective analysis of a single cell data repository. The data were then validated at both gene and protein level by performing RT-qPCR and two-colour immunohistochemistry on a library of second-trimester human fetal tissues. FINDINGS: TMPRSS2 is present at both gene and protein level in the predominantly epithelial fetal tissues analysed. ACE2 is present at significant levels only in the fetal intestine and kidney, and is not expressed in the fetal lung. The placenta also does not co-express the two proteins across the second trimester or at term. INTERPRETATION: This dataset indicates that the lungs are unlikely to be a viable route of SARS-CoV2 fetal infection. The fetal kidney, despite presenting both the proteins required for the infection, is anatomically protected from the exposure to the virus. However, the gastrointestinal tract is likely to be susceptible to infection due to its high co-expression of both proteins, as well as its exposure to potentially infected amniotic fluid. TWEETABLE ABSTRACT: This work provides detailed mechanistic insight into the relative protection & vulnerabilities of the fetus & placenta to SARS-CoV-2 infection by scRNAseq & protein expression analysis for ACE2 & TMPRSS2. The findings help to explain the low rate of vertical transmission. ispartof: BJOG vol:129 issue:2 pages:256-266 ispartof: location:England status: published

The establishment of in vitro naive human pluripotent stem cell cultures opened new perspectives for the study of early events in human development. The role of several transcription factors and signaling pathways have been characterized during maintenance of human naive pluripotency. However, little is known about the role exerted by the extracellular matrix (ECM) and its three-dimensional (3D) organization. Here, using an unbiased and integrated approach combining microfluidic cultures with transcriptional, proteomic, and secretome analyses, we found that naive, but not primed, hiPSC colonies are characterized by a self-organized ECM-rich microenvironment. Based on this, we developed a 3D culture system that supports robust long-term feeder-free self-renewal of naive hiPSCs and also allows direct and timely developmental morphogenesis simply by modulating the signaling environment. Our study opens new perspectives for future applications of naive hiPSCs to study critical stages of human development in 3D starting from a single cell.

The circadian system cyclically regulates many physiological and behavioral processes within the day. Desynchronization between physiological and behavioral rhythms increases the risk of developing some, including metabolic, disorders. Here we investigate how the oscillatory nature of metabolic signals, resembling feeding-fasting cycles, sustains the cell-autonomous clock in peripheral tissues. By controlling the timing, period and frequency of glucose and insulin signals via microfluidics, we find a strong effect on Per2::Luc fibroblasts entrainment. We show that the circadian Per2 expression is better sustained via a 24 h period and 12 h:12 h frequency-encoded metabolic stimulation applied for 3 daily cycles, aligned to the cell-autonomous clock, entraining the expression of hundreds of genes mostly belonging to circadian rhythms and cell cycle pathways. On the contrary misaligned feeding-fasting cycles synchronize and amplify the expression of extracellular matrix-associated genes, aligned during the light phase. This study underlines the role of the synchronicity between life-style-associated metabolic signals and peripheral clocks on the circadian entrainment., Chronic desynchronization between physiological and behavioral rhythms has been linked to the onset of metabolic diseases. Here the authors control the cyclic metabolic signals in a microfluidic device to study the effects of the timing, period and frequency of glucose and insulin on the transcriptome of cultured fibroblasts.

Thanks to innovative sample-preparation and sequencing technologies, gene expression in individual cells can now be measured for thousands of cells in a single experiment. Since its introduction, single-cell RNA sequencing (scRNA-seq) approaches have revolutionized the genomics field as they created unprecedented opportunities for resolving cell heterogeneity by exploring gene expression profiles at a single-cell resolution. However, the rapidly evolving field of scRNA-seq invoked the emergence of various analytics approaches aimed to maximize the full potential of this novel strategy. Unlike population-based RNA sequencing approaches, scRNA seq necessitates comprehensive computational tools to address high data complexity and keep up with the emerging single-cell associated challenges. Despite the vast number of analytical methods, a universal standardization is lacking. While this reflects the fields' immaturity, it may also encumber a newcomer to blend in.In this review, we aim to bridge over the abovementioned hurdle and propose four ready-to-use pipelines for scRNA-seq analysis easily accessible by a newcomer, that could fit various biological data types. Here we provide an overview of the currently available single-cell technologies for cell isolation and library preparation and a step by step guide that covers the entire canonical analytic workflow to analyse scRNA-seq data including read mapping, quality controls, gene expression quantification, normalization, feature selection, dimensionality reduction, and cell clustering useful for trajectory inference and differential expression. Such workflow guidelines will escort novices as well as expert users in the analysis of complex scRNA-seq datasets, thus further expanding the research potential of single-cell approaches in basic science, and envisaging its future implementation as best practice in the field.

Background: Disruption of alternative splicing (AS) is frequently observed in cancer and might represent an important signature for tumor progression and therapy. Exon skipping (ES) represents one of the most frequent AS events, and in non-small cell lung cancer (NSCLC) MET exon 14 skipping was shown to be targetable. Methods: We constructed neural networks (NN/CNN) specifically designed to detect MET exon 14 skipping events using RNAseq data. Furthermore, for discovery purposes we also developed a sparsely connected autoencoder to identify uncharacterized MET isoforms. Results: The neural networks had a Met exon 14 skipping detection rate greater than 94% when tested on a manually curated set of 690 TCGA bronchus and lung samples. When globally applied to 2605 TCGA samples, we observed that the majority of false positives was characterized by a blurry coverage of exon 14, but interestingly they share a common coverage peak in the second intron and we speculate that this event could be the transcription signature of a LINE1 (Long Interspersed Nuclear Element 1)-MET (Mesenchymal Epithelial Transition receptor tyrosine kinase) fusion. Conclusions: Taken together, our results indicate that neural networks can be an effective tool to provide a quick classification of pathological transcription events, and sparsely connected autoencoders could represent the basis for the development of an effective discovery tool.

Computational biology is enabling an explosive growth in our understanding of stem cells and our ability to use them for disease modeling, regenerative medicine, and drug discovery. We discuss four topics that exemplify applications of computation to stem cell biology: cell typing, lineage tracing, trajectory inference, and regulatory networks. We use these examples to articulate principles that have guided computational biology broadly and call for renewed attention to these principles as computation becomes increasingly important in stem cell biology. We also discuss important challenges for this field with the hope that it will inspire more to join this exciting area.

COVID-19 typically manifests as a respiratory illness, but several clinical reports have described gastrointestinal symptoms. This is particularly true in children in whom gastrointestinal symptoms are frequent and viral shedding outlasts viral clearance from the respiratory system. These observations raise the question of whether the virus can replicate within the stomach. Here we generate gastric organoids from fetal, pediatric, and adult biopsies as in vitro models of SARS-CoV-2 infection. To facilitate infection, we induce reverse polarity in the gastric organoids. We find that the pediatric and late fetal gastric organoids are susceptible to infection with SARS-CoV-2, while viral replication is significantly lower in undifferentiated organoids of early fetal and adult origin. We demonstrate that adult gastric organoids are more susceptible to infection following differentiation. We perform transcriptomic analysis to reveal a moderate innate antiviral response and a lack of differentially expressed genes belonging to the interferon family. Collectively, we show that the virus can efficiently infect the gastric epithelium, suggesting that the stomach might have an active role in fecal-oral SARS-CoV-2 transmission., Several clinical reports have described gastrointestinal symptoms for COVID-19, though whether the virus can replicate within the stomach remains unclear. Here the authors generate gastric organoids from human biopsies and show that the virus can efficiently infect gastric epithelium, suggesting that the stomach might have an active role in fecal-oral transmission.

Background: While pregnant women have been identified as a potentially at-risk group concerning COVID-19 infection, little is known regarding the susceptibility of the fetus to infection. Co-expression of ACE2 and TMPRSS2 has been identified as a pre-requisite for infection, and expression across different tissues is known to vary between children and adults. However, the expression of these proteins in the fetus is unknown. Methods: We performed a retrospective analysis of single cell data repositories. This data was then validated at both gene and protein level by performing qRT-PCR and two-colour immunohistochemistry on a library of second-trimester human fetal tissues. Findings: TMPRSS2 is present at both gene and protein level in the predominantly epithelial fetal tissues analysed. ACE2 is present at significant levels, only in the fetal intestine and kidney and is not expressed in the fetal lung. The placenta is also negative for the two proteins both during development and at term. Interpretation: This dataset indicates that the lungs are unlikely to be a viable route of SARS-CoV2 fetal infection. The fetal kidney, despite presenting both the proteins required for the infection, is anatomically protected from the exposure to the virus. However, the GI tract is likely to be susceptible to infection due to its high co-expression of both proteins, as well as its exposure to potentially infected amniotic fluid. Funding Information: This work was made possible by an MRC / UKRI COVID-19 Rapid response initiative grant (MR/V028480/1). Declaration of Interests: The authors declare no conflicts of interest related to this work or its developments. DC is founder, shareholder, and consultant of Next Generation Diagnostic SRL. Ethics Approval Statement: Human fetal tissues were obtained with consent through the Human Developmental Biology Resource (HDBR; REC 18/LO/0822 – IRAS 244325; Project ID 2000478). Placental samples were obtained at delivery of an uncomplicated, full-term pregnancy (median 39 weeks PCW [Range 38+1 -39+4] for 6 patients recruited through the EVERREST Prospective Study as normal controls (National Research Ethics reference 13/LO/1254), NCT02097667 registered 31st October 2013[10].

Thanks to innovative sample-preparation and sequencing technologies, gene expression in individual cells can now be measured for thousands of cells in a single experiment. Since its introduction, single-cell RNA sequencing (scRNA-seq) approaches have revolutionized the genomics field as they created unprecedented opportunities for resolving cell heterogeneity by exploring gene expression profiles at a single-cell resolution. However, the rapidly evolving field of scRNA-seq invoked the emergence of various analytics approaches aimed to maximize the full potential of this novel strategy. Unlike population-based RNA sequencing approaches, scRNA seq necessitates comprehensive computational tools to address high data complexity and keep up with the emerging single-cell associated challenges. Despite the vast number of analytical methods, a universal standardization is lacking. While this reflects the fields’ immaturity, it may also encumber a newcomer to blend in. In this review, we aim to bridge over the abovementioned hurdle and propose four ready-to-use pipelines for scRNA-seq analysis easily accessible by a newcomer, that could fit various biological data types. Here we provide an overview of the currently available single-cell technologies for cell isolation and library preparation and a step by step guide that covers the entire canonical analytic workflow to analyse scRNA-seq data including read mapping, quality controls, gene expression quantification, normalization, feature selection, dimensionality reduction, and cell clustering useful for trajectory inference and differential expression. Such workflow guidelines will escort novices as well as expert users in the analysis of complex scRNA-seq datasets, thus further expanding the research potential of single-cell approaches in basic science, and envisaging its future implementation as best practice in the field.

The Yes-associated protein (YAP), one of the major effectors of the Hippo pathway together with its related protein WW-domain-containing transcription regulator 1 (WWTR1; also known as TAZ), mediates a range of cellular processes from proliferation and death to morphogenesis. YAP and WW-domain-containing transcription regulator 1 (WWTR1; also known as TAZ) regulate a large number of target genes, acting as coactivators of DNA-binding transcription factors or as negative regulators of transcription by interacting with the nucleosome remodeling and histone deacetylase complexes. YAP is expressed in self-renewing embryonic stem cells (ESCs), although it is still debated whether it plays any crucial roles in the control of either stemness or differentiation. Here we show that the transient downregulation of YAP in mouse ESCs perturbs cellular homeostasis, leading to the inability to differentiate properly. Bisulfite genomic sequencing revealed that this transient knockdown caused a genome-wide alteration of the DNA methylation remodeling that takes place during the early steps of differentiation, suggesting that the phenotype we observed might be due to the dysregulation of some of the mechanisms involved in regulation of ESC exit from pluripotency. By gene expression analysis, we identified two molecules that could have a role in the altered genome-wide methylation profile: the long noncoding RNA ephemeron, whose rapid upregulation is crucial for the transition of ESCs into epiblast, and the methyltransferase-like protein Dnmt3l, which, during the embryo development, cooperates with Dnmt3a and Dnmt3b to contribute to the de novo DNA methylation that governs early steps of ESC differentiation. These data suggest a new role for YAP in the governance of the epigenetic dynamics of exit from pluripotency.

Coronavirus disease 2019 (COVID-19) pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection is a global public health emergency. COVID-19 typically manifests as a respiratory illness but an increasing number of clinical reports describe gastrointestinal (GI) symptoms. This is particularly true in children in whom GI symptoms are frequent and viral shedding outlasts viral clearance from the respiratory system. By contrast, fetuses seem to be rarely affected by COVID-19, although the virus has been detected in placentas of affected women. These observations raise the question of whether the virus can infect and replicate within the stomach once ingested. Moreover, it is not yet clear whether active replication of SARS-CoV-2 is possible in the stomach of children or in fetuses at different developmental stages. Here we show the novel derivation of fetal gastric organoids from 8-21 post-conception week (PCW) fetuses, and from pediatric biopsies, to be used as an in vitro model for SARS-CoV-2 gastric infection. Gastric organoids recapitulate human stomach with linear increase of gastric mucin 5AC along developmental stages, and expression of gastric markers pepsinogen, somatostatin, gastrin and chromogranin A. In order to investigate SARS-CoV-2 infection with minimal perturbation and under steady-state conditions, we induced a reversed polarity in the gastric organoids (RP-GOs) in suspension. In this condition of exposed apical polarity, the virus can easily access viral receptor angiotensin-converting enzyme 2 (ACE2). The pediatric RP-GOs are fully susceptible to infection with SARS-CoV-2, where viral nucleoprotein is expressed in cells undergoing programmed cell death, while the efficiency of infection is significantly lower in fetal organoids. The RP-GOs derived from pediatric patients show sustained robust viral replication of SARS-CoV-2, compared with organoids derived from fetal stomachs. Transcriptomic analysis shows a moderate innate antiviral response and the lack of differentially expressed genes belonging to the interferon family. Collectively, we established the first expandable human gastric organoid culture across fetal developmental stages, and we support the hypothesis that fetal tissue seems to be less susceptible to SARS-CoV-2 infection, especially in early stages of development. However, the virus can efficiently infect gastric epithelium in pediatric patients, suggesting that the stomach might have an active role in fecal-oral transmission of SARS-CoV-2.

Summary Controlling cell fate has great potential for regenerative medicine, drug discovery, and basic research. Although transcription factors are able to promote cell reprogramming and transdifferentiation, methods based on their upregulation often show low efficiency. Small molecules that can facilitate conversion between cell types can ameliorate this problem working through safe, rapid, and reversible mechanisms. Here, we present DECCODE, an unbiased computational method for identification of such molecules based on transcriptional data. DECCODE matches a large collection of drug-induced profiles for drug treatments against a large dataset of primary cell transcriptional profiles to identify drugs that either alone or in combination enhance cell reprogramming and cell conversion. Extensive validation in the context of human induced pluripotent stem cells shows that DECCODE is able to prioritize drugs and drug combinations enhancing cell reprogramming. We also provide predictions for cell conversion with single drugs and drug combinations for 145 different cell types., Graphical abstract, Highlights • DECCODE method for identification of drugs that promote cell conversion • Predicts drugs that alone or in combination increase reprogramming efficiency • Validated for reprogramming of human fibroblast to hiPSCs • Treatment suggestions provided for 145 target cell types, In this article, Napolitano, Rapakoulia, and colleagues present DECCODE, a method for automatic identification of drugs that alone or in combination promote cell conversion and reprogramming. They validate the method for reprogramming of human fibroblasts to induced pluripotent stem cells (hiPSCs), and provide predicted treatments for conversion to 145 target cell types.

The specification of cell identity during organ development is strictly controlled by extrinsic signals that restrict and define distinct cell fates. However, it is still not clear how cells, when exposed to exogenous signals, activate secretory cascades involving morphogens, growth factors and cytokines, extracellular matrix (ECM) deposition and remodeling. Here, we investigated the proteins secreted by cells in response to developmental exogenous signals, during the progression from endoderm to the hepatic lineage. A microfluidics-based approach coupled with SILAC-MS-based quantitative proteomic analysis revealed, among the 244 endogenously secreted proteins detected, high abundancy of ECM-associated proteins. Hepatocyte-like cells derived in microfluidics, where accumulation of cell-secreted proteins is enhanced up to 7-fold, displayed a more mature hepatic transcriptomic signature and 1.5-fold higher ammonia detoxification capacity compared to conventional culture conditions. Moreover, in the microfluidics-confined environment we observed organized deposition of COL1, FN, LAM and COL4, consistent with observations in human fetal liver at 8-15pcw.Then we tested if the exogenous supplementation of soluble ECM proteins identified by microfluidics-based SILAC-MS proteomic analysis, increase the 3D self-organization capacity of hepatic progenitor cells. We found that FN significantly enhances the hepatic organoid formation capacity of hiPSCs differentiated in conventional culture systems. These nascent organoids can be rapidly expanded for several passages and further differentiated to mature hepatocytes with significant increase of major hepatic functions, including ammonia detoxification, ALB and AAT secretion.

Pluripotency is the potential of a single cell to give rise to all embryonic lineages and first emerges in the naive epiblast of the preimplantation embryo. It has been proposed that upon implantation, epiblast cells transit to a formative phase, which is preparatory for their differentiation into all somatic lineages and primordial germ cells (PGCs). Murine naive embryonic stem cells (ESCs) recapitulate the molecular and functional properties of the naive epiblast, including the capacity to acquire a formative state and differentiate. However, the network of regulators and functional relevance of formative transition remain unresolved. Here we observe that differentiating ESCs transiently activate a distinct transcriptional program consistent with a formative state, after whose completion cells are irreversibly committed to differentiate. To our surprise, we observed that Esrrb, a pivotal naive pluripotency factor, is both sufficient and required to activate the formative program. Mechanistically, in naive cells ESRRB occupies both naive and formative gene loci. During formative transition ESRRB binding at naive genes is lost, while binding on formative genes is consolidated. Finally, when both naive and formative transcriptional programs are inactivated, ESRRB occupancy is mostly lost and cells irreversibly commit to differentiate. Genetic inactivation of Esrrb leads to failure to induce the appropriate formative program, which functionally results in severely impaired PGC specification and accelerated spontaneous mesendoderm differentiation. Thus, Esrrb is critical for activating the formative transition and consequently for executing timely and unbiased multilineage differentiation of murine pluripotent cells. We propose that similar in-built differentiation circuits might be found in other species and stem cell types.

Background High-grade serous ovarian cancer (HGSOC) is a major unmet need in oncology. The remaining uncertainty on its originating tissue has hampered the discovery of molecular oncogenic pathways and the development of effective therapies. Methods We used an approach based on the retention in tumors of a DNA methylation trace (OriPrint) that distinguishes the two putative tissues of origin of HGSOC, the fimbrial (FI) and ovarian surface epithelia (OSE), to stratify HGSOC by several clustering methods, both linear and non-linear. The identified tumor subtypes (FI-like and OSE-like HGSOC) were investigated at the RNAseq level to stratify an in-house cohort of macrodissected HGSOC FFPE samples to derive overall and disease-free survival and identify specific transcriptional alterations of the two tumor subtypes, both by classical differential expression and weighted correlation network analysis. We translated our strategy to published datasets and verified the co-occurrence of previously described molecular classification of HGSOC. We performed cytokine analysis coupled to immune phenotyping to verify alterations in the immune compartment associated with HGSOC. We identified genes that are both differentially expressed and methylated in the two tumor subtypes, concentrating on PAX8 as a bona fide marker of FI-like HGSOC. Results We show that: - OriPrint is a robust DNA methylation tracer that exposes the tissue of origin of HGSOC. - The tissue of origin of HGSOC is the main determinant of DNA methylation variance in HGSOC. - The tissue of origin is a prognostic factor for HGSOC patients. - FI-like and OSE-like HGSOC are endowed with specific transcriptional alterations that impact patients’ prognosis. - OSE-like tumors present a more invasive and immunomodulatory phenotype, compatible with its worse prognostic impact. - Among genes that are differentially expressed and regulated in FI-like and OSE-like HGSOC, PAX8 is a bona fide marker of FI-like tumors. Conclusions Through an integrated approach, our work demonstrates that both FI and OSE are possible origins for human HGSOC, whose derived subtypes are both molecularly and clinically distinct. These results will help define a new roadmap towards rational, subtype-specific therapeutic inroads and improved patients’ care.

Summary The specification of the hepatic identity during human liver development is strictly controlled by extrinsic signals, yet it is still not clear how cells respond to these exogenous signals by activating secretory cascades, which are extremely relevant, especially in 3D self-organizing systems. Here, we investigate how the proteins secreted by human pluripotent stem cells (hPSCs) in response to developmental exogenous signals affect the progression from endoderm to the hepatic lineage, including their competence to generate nascent hepatic organoids. By using microfluidic confined environment and stable isotope labeling with amino acids in cell culture-coupled mass spectrometry (SILAC-MS) quantitative proteomic analysis, we find high abundancy of extracellular matrix (ECM)-associated proteins. Hepatic progenitor cells either derived in microfluidics or exposed to exogenous ECM stimuli show a significantly higher potential of forming hepatic organoids that can be rapidly expanded for several passages and further differentiated into functional hepatocytes. These results prove an additional control over the efficiency of hepatic organoid formation and differentiation for downstream applications., Graphical Abstract, Highlights • Microfluidic confined environment enhances hepatic differentiation of hPSCs • SILAC-based proteomic analysis reveals high abundance of secreted ECM proteins • ECM deposition and remodeling correlate with cell-ECM receptor overexpression • Either endogenous or exogenous ECM enhances organoid formation and differentiation, Michielin et al. investigate the secretome of human pluripotent stem cells undergoing hepatic differentiation by coupling microfluidics with SILAC proteomic analysis. They reveal a role of soluble ECM protein accumulation and deposition and leverage these insights to efficiently and robustly derive hepatic organoids from hiPSCs.

Organoids have extensive therapeutic potential and are increasingly opening up new avenues within regenerative medicine. However, their clinical application is greatly limited by the lack of effective GMP-compliant systems for organoid expansion in culture. Here, we envisage that the use of extracellular matrix (ECM) hydrogels derived from decellularized tissues (DT) can provide an environment capable of directing cell growth. These gels possess the biochemical signature of tissue-specific ECM and have the potential for clinical translation. Gels from decellularized porcine small intestine (SI) mucosa/submucosa enable formation and growth of endoderm-derived human organoids, such as gastric, hepatic, pancreatic, and SI. ECM gels can be used as a tool for direct human organoid derivation, for cell growth with a stable transcriptomic signature, and for in vivo organoid delivery. The development of these ECM-derived hydrogels opens up the potential for human organoids to be used clinically., Organoid cultures have been developed from multiple tissues, opening new possibilities for regenerative medicine. Here the authors demonstrate the derivation of GMP-compliant hydrogels from decellularized porcine small intestine which support formation and growth of human gastric, liver, pancreatic and small intestinal organoids.

In normal mammalian development cytosine methylation is essential and is directed to specific regions of the genome. Despite notable advances through mapping its genome-wide distribution, studying the direct contribution of DNA methylation to gene and genome regulation has been limited by the lack of tools for its precise manipulation. Thus, combining the targeting capability of the CRISPR–Cas9 system with an epigenetic modifier has attracted interest in the scientific community. In contrast to profiling the genome-wide cleavage of a nuclease competent Cas9, tracing the global activity of a dead Cas9 (dCas9) methyltransferase fusion protein is challenging within a highly methylated genome. Here, we report the generation and use of an engineered, methylation depleted but maintenance competent mouse ES cell line and find surprisingly ubiquitous nuclear activity of dCas9-methyltransferases. Subsequent experiments in human somatic cells refine these observations and point to an important difference between genetic and epigenetic editing tools that require unique experimental considerations., Catalytically inactive Cas9 fused to a methyltransferase has emerged as a promising epigenome modifying tool. Here the authors generate a methylation depleted but maintenance competent mouse ES cell line and find ubiquitous off-target activity.

Transcription factors (TFs) direct developmental transitions by binding to target DNA sequences, influencing gene expression and establishing complex gene-regultory networks. To systematically determine the molecular components that enable or constrain TF activity, we investigated the genomic occupancy of FOXA2, GATA4 and OCT4 in several cell types. Despite their classification as pioneer factors, all three TFs exhibit cell-type-specific binding, even when supraphysiologically and ectopically expressed. However, FOXA2 and GATA4 can be distinguished by low enrichment at loci that are highly occupied by these factors in alternative cell types. We find that expression of additional cofactors increases enrichment at a subset of these sites. Finally, FOXA2 occupancy and changes to DNA accessibility can occur in G1-arrested cells, but subsequent loss of DNA methylation requires DNA replication.

Summary RNA-binding proteins (RBPs) and long non-coding RNAs (lncRNAs) are key regulators of gene expression, but their joint functions in coordinating cell fate decisions are poorly understood. Here we show that the expression and activity of the RBP TDP-43 and the long isoform of the lncRNA Neat1, the scaffold of the nuclear compartment “paraspeckles,” are reciprocal in pluripotent and differentiated cells because of their cross-regulation. In pluripotent cells, TDP-43 represses the formation of paraspeckles by enhancing the polyadenylated short isoform of Neat1. TDP-43 also promotes pluripotency by regulating alternative polyadenylation of transcripts encoding pluripotency factors, including Sox2, which partially protects its 3′ UTR from miR-21-mediated degradation. Conversely, paraspeckles sequester TDP-43 and other RBPs from mRNAs and promote exit from pluripotency and embryonic patterning in the mouse. We demonstrate that cross-regulation between TDP-43 and Neat1 is essential for their efficient regulation of a broad network of genes and, therefore, of pluripotency and differentiation., Graphical Abstract, Highlights • TDP-43 maintains pluripotency by regulating expression of pluripotency factors • TDP-43 represses formation of paraspeckles in ESCs by regulating Neat1 • The paraspeckle-inducing isoform of Neat1 promotes differentiation of ESCs and embryos • Cross-regulation between TDP-43 and Neat1 enhances pluripotency-differentiation axis, Modic et al. uncover opposing roles of TDP-43 and paraspeckles in pluripotency and differentiation that are further enhanced by their cross-regulation. TDP-43 represses paraspeckles through processing of the scaffolding lncRNA Neat1, whereas paraspeckles partially sequester TDP-43. This reciprocal relationship promotes coordinated changes in alternative polyadenylation essential for efficient exit from pluripotency.

MicroRNAs (miRNAs) are attractive therapeutic targets and promising candidates as molecular biomarkers for various therapy-resistant tumors. However, the association between miRNAs and drug resistance in melanoma remains to be elucidated. We used an integrative genomic analysis to comprehensively study the miRNA expression profiles of drug-resistant melanoma patients and cell lines. MicroRNA-181a and -181b (miR181a/b) were identified as the most significantly down-regulated miRNAs in resistant melanoma patients and cell lines. Re-establishment of miR-181a/b expression reverses the resistance of melanoma cells to the BRAF inhibitor dabrafenib. Introduction of miR-181 mimics markedly decreases the expression of TFAM in A375 melanoma cells resistant to BRAF inhibitors. Furthermore, melanoma growth was inhibited in A375 and M14 resistant melanoma cells transfected with miR-181a/b mimics, while miR-181a/b depletion enhanced resistance in sensitive cell lines. Collectively, our study demonstrated that miR-181a/b could reverse the resistance to BRAF inhibitors in dabrafenib resistant melanoma cell lines. In addition, miR-181a and -181b are strongly down-regulated in tumor samples from patients before and after the development of resistance to targeted therapies. Finally, melanoma tissues with high miR-181a and -181b expression presented favorable outcomes in terms of Progression Free Survival, suggesting that miR-181 is a clinically relevant candidate for therapeutic development or biomarker-based therapy selection.