Search

Centromere identity is determined by the specific deposition of CENP-A, a histone H3 variant localizing exclusively at centromeres. Increased CENP-A expression, which is a frequent event in cancer, causes mislocalization, ectopic kinetochore assembly and genomic instability. Proteolysis regulates CENP-A expression and prevents its misincorporation across chromatin. How proteolysis restricts CENP-A localization to centromeres is not well understood. Here we report that, in Drosophila, CENP-ACID expression levels are regulated throughout the cell cycle by the combined action of SCFPpa and APC/CCdh1. We show that SCFPpa regulates CENP-ACID expression in G1 and, importantly, in S-phase preventing its promiscuous incorporation across chromatin during replication. In G1, CENP-ACID expression is also regulated by APC/CCdh1. We also show that Cal1, the specific chaperone that deposits CENP-ACID at centromeres, protects CENP-ACID from SCFPpa-mediated degradation but not from APC/CCdh1-mediated degradation. These results suggest that, whereas SCFPpa targets the fraction of CENP-ACID that is not in complex with Cal1, APC/CCdh1 mediates also degradation of the Cal1-CENP-ACID complex and, thus, likely contributes to the regulation of centromeric CENP-ACID deposition., MINECO [BFU2015-65082-P]; Generalitat de Catalunya [SGR2014-204, SGR2017-475]; European Community FEDER program; ‘Centre de Referència en Biotecnologia’ of the Generalitat de Catalunya. Funding for open access charge: MINECO [BFU2015-65082-P]; Generalitat de Catalunya [SGR2014-204, SGR2017-475]; European Community FEDER program.

© The Author(s) 2020, Barrier-to-Autointegration Factor (BAF) is a conserved nuclear envelope (NE) component that binds chromatin and helps its anchoring to the NE. Cycles of phosphorylation and dephosphorylation control BAF function. Entering mitosis, phosphorylation releases BAF from chromatin and facilitates NE-disassembly. At mitotic exit, PP2A-mediated dephosphorylation restores chromatin binding and nucleates NE-reassembly. Here, we show that in Drosophila a small fraction of BAF (cenBAF) associates with centromeres. We also find that PP4 phosphatase, which is recruited to centromeres by CENP-C, prevents phosphorylation and release of cenBAF during mitosis. cenBAF is necessary for proper centromere assembly and accurate chromosome segregation, being critical for mitosis progression. Disrupting cenBAF localization prevents PP2A inactivation in mitosis compromising global BAF phosphorylation, which in turn leads to its persistent association with chromatin, delays anaphase onset and causes NE defects. These results suggest that, together with PP4 and CENP-C, cenBAF forms a centromere-based mechanism that controls chromosome segregation and mitosis progression., This work was supported by grants from MICINN (BFU2015-65082-P and PGC2018-094538-B-I00), the Generalitat de Catalunya (SGR2009-1023, SGR2014-204) and the European Community FEDER program to F.A., and the Ministry for National Economy of Hungary (GINOP-2.3.2-15-2016-00032 and GINOP-2.3.2-15-2016-00001) and the Hungarian Academy of Sciences (LP2017-7/2017) to Z.L. Work in MRP lab is supported by The Wellcome Trust. This work was carried out within the framework of the “Centre de Referència en Biotecnologia” of the “Generalitat de Catalunya”. S.M.-G. acknowledges receipt of an FPU fellowship from the MINECO. P.E. acknowledges receipt of an FPI fellowship from MINECO.

In an earlier paper (Pérez-Montero et al., 2013), we reported that the embryonic linker histone of Drosophila dBigH1 was essential for early Drosophila embryogenesis since embryos homozygous for the bigH1100 mutation showed strong defects and did not survive beyond zygotic genome activation (ZGA) at cellularization. Recent results challenge these observations since null bigH1 mutations generated by CRISPR/Cas9 methodology turn out to be homozygous viable, as reported in Li et al. (2019) and here. In this regard, Li et al. described a novel mechanism by which lack of dBigH1 is compensated by the early expression of maternal dH1. Here, we confirm this observation and show that such compensatory mechanism is not activated in bigH1100 embryos.

1Abstract1.1BackgroundsIn the last years we have faced an unprecedented growth in the availability of high-throughput epigenomics data related to the genomic distribution of epigenetic marks, namely transcription factors, histone modifications and other DNA binding proteins. This also pointed out the need for efficient tools for integration, visualization and functional analysis of genomics and epigenomics data. On this subject, we previously developed a computational framework, chroGPS, to integrate and visualize the associations between epigenetic factors and their relation to functional genetic elements in low-dimensional maps. We demonstrated the usefulness of our approach with several practical case studies based on well-defined biological hypothesis.1.2ResultsHere we introduce chroGPS version 2, a major update of our previously developed software with new functionalities for differential analysis of epigenomes. Methods are provided for efficient integration and comparison of data from different conditions or biological backgrounds, accounting and adjusting for systematic biases in order to provide an efficient and statistically robust base for differential analysis. We also include new useful functionalities for general data assessment and quality control prior to comparing maps, such as functions to study chromatin domain conservation between epigenomic backgrounds, to detect gross technical outliers and also to help in the selection of candidate marks for de-novo epigenome mapping. Our software, implemented in R as a Bioconductor package, provides detailed reference and user manuals to allow the final user to reproduce the presented case studies and use them as a starting point for generating and exploring epigenetic maps according to their own experimental needs.1.3ConclusionchroGPS2 extends our previously developed software, providing now a complete, intuitive, efficient and statistically robust framework for generation, visualization, characterization and differential analysis of epigenomic maps, in a way which is easy to adapt to different biological and technical backgrounds allowing exploration and hypothesis testing in multiple biological scenarios.

Chromatin is known to undergo extensive remodeling during nuclear reprogramming. However, the factors and mechanisms involved in this remodeling are still poorly understood and current experimental approaches to study it are not best suited for molecular and genetic analyses. Here we report on the use of Drosophila preblastodermic embryo extracts (DREX) in chromatin remodeling experiments. Our results show that incubation of somatic nuclei in DREX induces changes in chromatin organization similar to those associated with nuclear reprogramming, such as rapid binding of the germline specific linker histone dBigH1 variant to somatic chromatin, heterochromatin reorganization, changes in the epigenetic state of chromatin, and nuclear lamin disassembly. These results raise the possibility of using the powerful tools of Drosophila genetics for the analysis of chromatin changes associated with this essential process., This work was supported by grants from MINECO (BFU2015-65082-P), the Generalitat de Catalunya (SGR2014-204), and the European Community FEDER program. This work was carried out within the framework of the “Centre de Referència en Biotecnologia” of the Generalitat de Catalunya. EŠ acknowledges receipt of a NEWFELPRO Fellowship of the Croatian Government and Ministry of Science and Education within EU FP7 Programme framework.

Drosophila spermatogenesis constitutes a paradigmatic system to study maintenance, proliferation, and differentiation of adult stem cell lineages. Each Drosophila testis contains 6–12 germ stem cells (GSCs) that divide asymmetrically to produce gonialblast cells that undergo four transit-amplifying (TA) spermatogonial divisions before entering spermatocyte differentiation. Mechanisms governing these crucial transitions are not fully understood. Here, we report the essential role of the germline linker histone dBigH1 during early spermatogenesis. Our results suggest that dBigH1 is a general silencing factor that represses Bam, a key regulator of spermatogonia proliferation that is silenced in spermatocytes. Reciprocally, Bam represses dBigH1 during TA divisions. This double-repressor mechanism switches dBigH1/Bam expression from off/on in spermatogonia to on/off in spermatocytes, regulating progression into spermatocyte differentiation. dBigH1 is also required for GSC maintenance and differentiation. These results show the critical importance of germline H1s for male GSC lineage differentiation, unveiling a regulatory interaction that couples transcriptional and translational repression., This work was supported by grants from the MINECO (BFU2012-30724 and BFU2015-65082P), the Generalitat de Catalunya (SGR2009-1023 and SGR2014-204), and the European Community FEDER program. This work was carried out within the framework of the ‘‘Centre de Refere` ncia en Biotecnologia’’ of the ‘‘Generalitat de Catalunya.’’ S.P.-M. and P.C.-C. acknowledge receipt of FPI fellowships from the MINECO.

Linker histone H1 is an important structural component of chromatin that stabilizes the nucleosome and compacts the nucleofilament into higher-order structures. The biology of histone H1 remains, however, poorly understood. Here we show that Drosophila histone H1 (dH1) prevents genome instability as indicated by the increased γH2Av (H2AvS137P) content and the high incidence of DNA breaks and sister-chromatid exchanges observed in dH1-depleted cells. Increased γH2Av occurs preferentially at heterochromatic elements, which are upregulated upon dH1 depletion, and is due to the abnormal accumulation of DNA:RNA hybrids (R-loops). R-loops accumulation is readily detectable in G1-phase, whereas γH2Av increases mainly during DNA replication. These defects induce JNK-mediated apoptosis and are specific of dH1 depletion since they are not observed when heterochromatin silencing is relieved by HP1a depletion. Altogether, our results suggest that histone H1 prevents R-loops-induced DNA damage in heterochromatin and unveil its essential contribution to maintenance of genome stability., This work was supported by grants from MICINN (BFU2012-30724 and BFU2015-65082-P), the Generalitat de Catalunya (SGR2014-204) and by the European Community FEDER program. A.B.-F. and A.C.-L. acknowledge receipt of FPU (MED) and FPI (MINECO) fellowships, respectively.

The centromere is a specialized chromosomal structure that dictates kinetochore assembly and, thus, is essential for accurate chromosome segregation. Centromere identity is determined epigenetically by the presence of a centromere‐specific histone H3 variant, CENP‐A, that replaces canonical H3 in centromeric chromatin. Here, we discuss recent work by Roulland et al. that identifies structural elements of the nucleosome as essential determinants of centromere function. In particular, CENP‐A nucleosomes have flexible DNA ends due to the short αN helix of CENP‐A. The higher flexibility of the DNA ends of centromeric nucleosomes impairs binding of linker histones H1, while it facilitates binding of other essential centromeric proteins, such as CENP‐C, and is required for mitotic fidelity. This work extends previous observations indicating that the differential structural properties of CENP‐A nucleosomes are on the basis of its contribution to centromere identity and function. Here, we discuss the implications of this work and the questions arising from it

Development of tools to jointly visualize the genome and the epigenome remains a challenge. chroGPS is a computational approach that addresses this question. chroGPS uses multidimensional scaling techniques to represent similarity between epigenetic factors, or between genetic elements on the basis of their epigenetic state, in 2D/3D reference maps. We emphasize biological interpretability, statistical robustness, integration of genetic and epigenetic data from heterogeneous sources, and computational feasibility. Although chroGPS is a general methodology to create reference maps and study the epigenetic state of any class of genetic element or genomic region, we focus on two specific kinds of maps: chroGPSfactors, which visualizes functional similarities between epigenetic factors, and chroGPSgenes, which describes the epigenetic state of genes and integrates gene expression and other functional data. We use data from the modENCODE project on the genomic distribution of a large collection of epigenetic factors in Drosophila, a model system extensively used to study genome organization and function. Our results show that the maps allow straightforward visualization of relationships between factors and elements, capturing relevant information about their functional properties that helps to interpret epigenetic information in a functional context and derive testable hypotheses. © 2013 The Author(s). Published by Oxford University Press, The Spanish ‘Ministerio de Economia y Competitividad’ [CSD2006-49, BFU2009-07111 and BFU2012-30724] and the ‘Generalitat de Catalunya’ [SGR2009-1023]; This work was carried out within the framework of the ‘Centre de Referència en Biotecnologia’ of the ‘Generalitat de Catalunya’. Funding for open access charge: Spanish ‘Ministerio de Economia y Competitividad’ [BFU2012-30724]

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License., H3K4me3 is a histone modification that accumulates at the transcription-start site (TSS) of active genes and is known to be important for transcription activation. The way in which H3K4me3 is regulated at TSS and the actual molecular basis of its contribution to transcription remain largely unanswered. To address these questions, we have analyzed the contribution of dKDM5/LID, the main H3K4me3 demethylase in Drosophila, to the regulation of the pattern of H3K4me3. ChIP-seq results show that, at developmental genes, dKDM5/LID localizes at TSS and regulates H3K4me3. dKDM5/LID target genes are highly transcribed and enriched in active RNApol II and H3K36me3, suggesting a positive contribution to transcription. Expression-profiling show that, though weakly, dKDM5/LID target genes are significantly downregulated upon dKDM5/LID depletion. Furthermore, dKDM5/LID depletion results in decreased RNApol II occupancy, particularly by the promoter-proximal Pol llo ser5 form. Our results also show that ASH2, an evolutionarily conserved factor that locates at TSS and is required for H3K4me3, binds and positively regulates dKDM5/LID target genes. However, dKDM5/LID and ASH2 do not bind simultaneously and recognize different chromatin states, enriched in H3K4me3 and not, respectively. These results indicate that, at developmental genes, dKDM5/LID and ASH2 coordinately regulate H3K4me3 at TSS and that this dynamic regulation contributes to transcription. © 2012 The Author(s)., Seed Funding for Applied Research (Project No. 201007160001 to M.S.Y.H.); URC-PDF Scheme, Centre for Cancer Research HKU [to S.M.H.S. and S.S.D. (in part)]; Faculty Development Fund. Funding for open access charge: Seed Funding for Applied Research, University of Hong Kong (Project No. 201007160001 to M.S.Y.H.).

Functional characterisation of vigilin, a highly conserved multi-KH-domain protein that binds RNA and ssDNA, remains elusive and, to some extent, controversial. Studies performed in Saccharomyces cerevisiae and human cells indicate that vigilin localises to the cytoplasm, binds ribosomes, associates to RER and regulates mRNA translation. On the other hand, we and others reported a contribution to heterochromatin-mediated gene silencing (PEV) and chromosome segregation in S. cerevisiae, Drosophila and human cells. Whether this contribution is direct remains, however, unclear. Here, we report that Drosophila vigilin, DDP1, vastly localises to the cytoplasm, being largely excluded from the nucleus. We also show that DDP1 preferentially associates to RER and co-purifies with several ribosomal proteins, suggesting a contribution to mRNA translation. In light of these results, the contribution of DDP1 to PEV was re-examined. Here, we show that a newly generated null ddp1Δ mutation is only a weak suppressor of PEV, which is in contrast with our own previous results showing dominant suppression in the presence of a strong hypomorphic ddp115.1 mutation. Similar results were obtained in the fission yeast Schizosaccharomyces pombe, where vigilin (Vgl1) also associates to RER, having no significant contribution to PEV at centromeres, telomeres and the mating-type locus. Altogether, these results indicate that cytoplasmic localisation and association to RER, but not contribution to heterochromatin organisation, are evolutionarily conserved features of vigilin, favouring a model by which vigilin acts in the cytoplasm, regulating RNA metabolism, and affects nuclear functions only indirectly. © 2010 Elsevier B.V., Este trabajo fue financiado por las subvenciones del Ministerio de Ciencia e Innovación, España (BFU2006-1627, CSD2006-49 y BFU2009-07111) y la Generalitat de Catalunya (SGR2005-678 y SGR2009-1023)

It was described earlier that the Drosophila GAGA factor [Trithorax-like (Trl)] interacts with dSAP18, which, in mammals, was reported to be a component of the Sin3-HDAC co-repressor complex. GAGA-dSAP18 interaction was proposed to contribute to the functional regulation of the bithorax complex (BX-C). Here, we show that mutant alleles of Trl, dsap18 and drpd3/hdac1 enhance A6-to-A5 transformation indicating a contribution to the regulation of d-B expression at A6. In A6, expression of Abd-B is driven by the iab-6 enhancer, which is insulated from iab-7 by the Fab-7 element. Here, we report that GAGA, dSAP18 and dRPD3/HDAC1 co-localize to ectopic Fab-7 sites in polytene chromosomes and that mutant Trl, dsap18 and drpd3/hdac1 alleles affect -dependent silencing. Consistent with these findings, chromatin immunoprecipitation analysis shows that, in Drosophila embryos, the endogenous Fab-7 element is hypoacetylated at histones H3 and H4. These results indicate a contribution of GAGA, dSAP18 and dRPD3/HDAC1 to the regulation of Fab-7 function. © The Author 2005. Published by Oxford University Press. All rights reserved., This work was supported by grants from the MCyT (GEN2001-4846-C05-03, BMC2002-00905) and the CIRIT (2001SGR00344) and the American Cancer Society (to S.D.H.). S.C. and S.P. acknowledge receipt of a doctoral fellowship from the MEC. This work was carried out within the framework of the ‘CeRBa’ of the Generalitat de Catalunya. Funding to pay the Open Access publication charges for this article was provided by MCyT and CIRIT

9 pages, 8 figures.-- PMID: 9733760 [PubMed]., The Drosophila GAGA factor binds specifically to simple repeating d(GA.TC)n DNA sequences. These sequences are known to be capable of forming triple-stranded DNA as well as other non-B-DNA conformations. Here, it is shown that GAGA binds to a d[CT(GA.TC)]22 intermolecular triplex with similar specificity and affinity as to a regular double-stranded B-form d(GA.TC)22 sequence. The interaction of GAGA with triplex DNA cannot, however, stimulate transcription in vitro. The affinity of GAGA for triplexes of the purine motif, such as a d[AG(GA.TC)]22 intermolecular triplex, is significantly lower. The DNA binding domain of GAGA is sufficient for efficient binding to triplex DNA. Based on the reported solution structure of the complex of GAGA-DNA binding domain with double-stranded DNA, a model for its interaction with triplex DNA is proposed in which most of the protein-DNA contacts observed in duplex DNA are maintained, especially those occurring through the minor groove. The higher negative charge of the triplex is likely to have also an important contribution to both the specificity and affinity of the interaction., This work was supported in part by Spanish DGES Grants PB96-812 (to F. A.) and PB96-1005 (to M. O.), European Union Grant BIO2-CT94-3069, and the CIRIT of the Generalitat de Catalunya Grant SGR95-570. This work was carried out in the context of the Centre de Referència en Biotecnologia of the Generalitat de Catalunya.

The simian virus 40 (SV40) enhancer contains three 8-bp purine-pyrimidine alternating sequences which are known to adopt the left-handed Z-DNA conformation in vitro. In this paper, we have undertaken the determination of the DNA conformation adopted by these Z-motifs in the SV40 minichromosome. We have analyzed the presence of Z-DNA through the change in linkage which should accompany formation of this left-handed conformation. Our results indicate that, regardless of the precise moment of the viral lytic cycle at which minichromosomes are harvested and the condition of the transfected DNA, either relaxed or negatively supercoiled, none of the three Z motifs of the SV40 enhancer exist to a significant extent as Z-DNA in SV40 minichromosomes. The SV40 enhancer adopts predominantly a right-handed B-DNA conformation in vivo, This work was financed by grants from the Comision Interministerial de Ciencia y Tecnología (BIO88-0236), the Fondo de Investigaciones Sanitarias (88/1447 and 89/0510), the Comisio Interdepartamental de Recerca i Innovació Tecnologica (89/4700) and the Commission of the European Communities [ST2J-0372-C(A) and BAP-0466.E(JR)]