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O'Haren T, Aoki T, Rieder LE. Zelda is dispensable for Drosophila melanogaster histone gene regulation. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.12.19.572383. [PMID: 38187550 PMCID: PMC10769256 DOI: 10.1101/2023.12.19.572383] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/09/2024]
Abstract
To ensure that the embryo can package exponentially increasing amounts of DNA, replication-dependent histones are some of the earliest transcribed genes from the zygotic genome. However, how the histone genes are identified is not known. The pioneer factors Zelda and CLAMP collaborate at a subset of genes to regulate zygotic genome activation in Drosophila melanogaster and target early activated genes to induce transcription. CLAMP also regulates the embryonic histone genes and helps establish the histone locus body, a suite of factors that controls histone mRNA biosynthesis. The relationship between Zelda and CLAMP led us to hypothesize that Zelda helps identify histone genes for early embryonic expression. We found that Zelda targets the histone locus early during embryogenesis, prior to histone gene expression. However, depletion of zelda in the early embryo does not affect histone mRNA levels or histone locus body formation. While surprising, these results concur with other investigations into Zelda's role in the early embryo, suggesting the earliest factors responsible for specifying the zygotic histone genes remain undiscovered.
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Affiliation(s)
- Tommy O'Haren
- Emory University Department of Biology, Atlanta, GA 30322, USA
| | - Tsutomu Aoki
- Department of Molecular Biology, Princeton University, Princeton, NJ 08540 USA
| | - Leila E Rieder
- Emory University Department of Biology, Atlanta, GA 30322, USA
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2
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Schmidt CA, Hodkinson LJ, Comstra HS, Khan S, Torres H, Rieder LE. A cost-free CURE: using bioinformatics to identify DNA-binding factors at a specific genomic locus. JOURNAL OF MICROBIOLOGY & BIOLOGY EDUCATION 2023; 24:e00120-23. [PMID: 38107989 PMCID: PMC10720551 DOI: 10.1128/jmbe.00120-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/20/2023] [Accepted: 09/14/2023] [Indexed: 12/19/2023]
Abstract
Research experiences provide diverse benefits for undergraduates. Many academic institutions have adopted course-based undergraduate research experiences (CUREs) to improve student access to research opportunities. However, potential instructors of a CURE might still face financial or practical hurdles that prevent implementation. Bioinformatics research offers an alternative that is free, safe, compatible with remote learning, and may be more accessible for students with disabilities. Here, we describe a bioinformatics CURE that leverages publicly available datasets to discover novel proteins that target an instructor-determined genomic locus of interest. We use the free, user-friendly bioinformatics platform Galaxy to map ChIP-seq datasets to a genome, which removes the computing burden from students. Both faculty and students directly benefit from this CURE, as faculty can perform candidate screens and publish CURE results. Students gain not only basic bioinformatics knowledge, but also transferable skills, including scientific communication, database navigation, and primary literature experience. The CURE is flexible and can be expanded to analyze different types of high-throughput data or to investigate different genomic loci in any species.
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Affiliation(s)
| | - Lauren J. Hodkinson
- Graduate Program in Genetics and Molecular Biology, Emory University, Atlanta, Georgia, USA
| | - H. Skye Comstra
- Department of Biology, Emory University, Atlanta, Georgia, USA
| | - Samia Khan
- Department of Biology, Emory University, Atlanta, Georgia, USA
| | | | - Leila E. Rieder
- Department of Biology, Emory University, Atlanta, Georgia, USA
- Graduate Program in Genetics and Molecular Biology, Emory University, Atlanta, Georgia, USA
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Dubruille R, Herbette M, Revel M, Horard B, Chang CH, Loppin B. Histone removal in sperm protects paternal chromosomes from premature division at fertilization. Science 2023; 382:725-731. [PMID: 37943933 PMCID: PMC11180706 DOI: 10.1126/science.adh0037] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2023] [Accepted: 09/22/2023] [Indexed: 11/12/2023]
Abstract
The global replacement of histones with protamines in sperm chromatin is widespread in animals, including insects, but its actual function remains enigmatic. We show that in the Drosophila paternal effect mutant paternal loss (pal), sperm chromatin retains germline histones H3 and H4 genome wide without impairing sperm viability. However, after fertilization, pal sperm chromosomes are targeted by the egg chromosomal passenger complex and engage into a catastrophic premature division in synchrony with female meiosis II. We show that pal encodes a rapidly evolving transition protein specifically required for the eviction of (H3-H4)2 tetramers from spermatid DNA after the removal of H2A-H2B dimers. Our study thus reveals an unsuspected role of histone eviction from insect sperm chromatin: safeguarding the integrity of the male pronucleus during female meiosis.
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Affiliation(s)
- Raphaälle Dubruille
- Laboratoire de Biologie et Modélisation de la Cellule, École Normale Supérieure de Lyon, CNRS UMR5239, Université Claude Bernard Lyon 1, Lyon, France
| | - Marion Herbette
- Laboratoire de Biologie et Modélisation de la Cellule, École Normale Supérieure de Lyon, CNRS UMR5239, Université Claude Bernard Lyon 1, Lyon, France
| | - Maxime Revel
- Laboratoire de Biologie et Modélisation de la Cellule, École Normale Supérieure de Lyon, CNRS UMR5239, Université Claude Bernard Lyon 1, Lyon, France
| | - Béatrice Horard
- Laboratoire de Biologie et Modélisation de la Cellule, École Normale Supérieure de Lyon, CNRS UMR5239, Université Claude Bernard Lyon 1, Lyon, France
| | - Ching-Ho Chang
- Division of Basic Sciences, Fred Hutchinson Cancer Center, Seattle, WA, USA
| | - Benjamin Loppin
- Laboratoire de Biologie et Modélisation de la Cellule, École Normale Supérieure de Lyon, CNRS UMR5239, Université Claude Bernard Lyon 1, Lyon, France
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4
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Llorens-Giralt P, Camilleri-Robles C, Corominas M, Climent-Cantó P. Chromatin Organization and Function in Drosophila. Cells 2021; 10:cells10092362. [PMID: 34572010 PMCID: PMC8465611 DOI: 10.3390/cells10092362] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2021] [Revised: 09/03/2021] [Accepted: 09/06/2021] [Indexed: 12/25/2022] Open
Abstract
Eukaryotic genomes are packaged into high-order chromatin structures organized in discrete territories inside the cell nucleus, which is surrounded by the nuclear envelope acting as a barrier. This chromatin organization is complex and dynamic and, thus, determining the spatial and temporal distribution and folding of chromosomes within the nucleus is critical for understanding the role of chromatin topology in genome function. Primarily focusing on the regulation of gene expression, we review here how the genome of Drosophila melanogaster is organized into the cell nucleus, from small scale histone–DNA interactions to chromosome and lamina interactions in the nuclear space.
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Abstract
Nucleosome dynamics and properties are central to all forms of genomic activities. Among the core histones, H3 variants play a pivotal role in modulating nucleosome structure and function. Here, we focus on the impact of H3 variants on various facets of development. The deposition of the replicative H3 variant following DNA replication is essential for the transmission of the epigenomic information encoded in posttranscriptional modifications. Through this process, replicative H3 maintains cell fate while, in contrast, the replacement H3.3 variant opposes cell differentiation during early embryogenesis. In later steps of development, H3.3 and specialized H3 variants are emerging as new, important regulators of terminal cell differentiation, including neurons and gametes. The specific pathways that regulate the dynamics of the deposition of H3.3 are paramount during reprogramming events that drive zygotic activation and the initiation of a new cycle of development.
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Affiliation(s)
- Benjamin Loppin
- Laboratoire de Biologie et de Modélisation de la Cellule, CNRS UMR 5239, Ecole Normale Supérieure de Lyon, University of Lyon, F-69007 Lyon, France;
| | - Frédéric Berger
- Gregor Mendel Institute (GMI), Austrian Academy of Sciences, Vienna BioCenter (VBC), 1030 Vienna, Austria;
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Chari S, Wilky H, Govindan J, Amodeo AA. Histone concentration regulates the cell cycle and transcription in early development. Development 2019; 146:dev.177402. [PMID: 31511251 DOI: 10.1242/dev.177402] [Citation(s) in RCA: 25] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2019] [Accepted: 08/28/2019] [Indexed: 12/12/2022]
Abstract
The early embryos of many animals, including flies, fish and frogs, have unusually rapid cell cycles and delayed onset of transcription. These divisions are dependent on maternally supplied RNAs and proteins including histones. Previous work suggests that the pool size of maternally provided histones can alter the timing of zygotic genome activation (ZGA) in frogs and fish. Here, we examine the effects of under- and overexpression of maternal histones in Drosophila embryogenesis. Decreasing histone concentration advances zygotic transcription, cell cycle elongation, Chk1 activation and gastrulation. Conversely, increasing histone concentration delays transcription and results in an additional nuclear cycle before gastrulation. Numerous zygotic transcripts are sensitive to histone concentration, and the promoters of histone-sensitive genes are associated with specific chromatin features linked to increased histone turnover. These include enrichment of the pioneer transcription factor Zelda, and lack of SIN3A and associated histone deacetylases. Our findings uncover a crucial regulatory role for histone concentrations in ZGA of Drosophila.
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Affiliation(s)
- Sudarshan Chari
- Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, NJ 08544, USA
| | - Henry Wilky
- Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, NJ 08544, USA
| | - Jayalakshmi Govindan
- Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, NJ 08544, USA
| | - Amanda A Amodeo
- Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, NJ 08544, USA
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Dorafshan E, Kahn TG, Glotov A, Savitsky M, Walther M, Reuter G, Schwartz YB. Ash1 counteracts Polycomb repression independent of histone H3 lysine 36 methylation. EMBO Rep 2019; 20:embr.201846762. [PMID: 30833342 DOI: 10.15252/embr.201846762] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2018] [Revised: 01/31/2019] [Accepted: 02/05/2019] [Indexed: 12/11/2022] Open
Abstract
Polycomb repression is critical for metazoan development. Equally important but less studied is the Trithorax system, which safeguards Polycomb target genes from the repression in cells where they have to remain active. It was proposed that the Trithorax system acts via methylation of histone H3 at lysine 4 and lysine 36 (H3K36), thereby inhibiting histone methyltransferase activity of the Polycomb complexes. Here we test this hypothesis by asking whether the Trithorax group protein Ash1 requires H3K36 methylation to counteract Polycomb repression. We show that Ash1 is the only Drosophila H3K36-specific methyltransferase necessary to prevent excessive Polycomb repression of homeotic genes. Unexpectedly, our experiments reveal no correlation between the extent of H3K36 methylation and the resistance to Polycomb repression. Furthermore, we find that complete substitution of the zygotic histone H3 with a variant in which lysine 36 is replaced by arginine does not cause excessive repression of homeotic genes. Our results suggest that the model, where the Trithorax group proteins methylate histone H3 to inhibit the histone methyltransferase activity of the Polycomb complexes, needs revision.
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Affiliation(s)
| | - Tatyana G Kahn
- Department of Molecular Biology, Umeå University, Umeå, Sweden
| | | | | | - Matthias Walther
- Institute of Developmental Genetics, Martin-Luther University of Halle-Wittenberg, Halle, Germany.,Max Planck Institute of Immunobiology and Epigenetics, Freiburg, Germany
| | - Gunter Reuter
- Institute of Developmental Genetics, Martin-Luther University of Halle-Wittenberg, Halle, Germany
| | - Yuri B Schwartz
- Department of Molecular Biology, Umeå University, Umeå, Sweden
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Shindo Y, Amodeo AA. Dynamics of Free and Chromatin-Bound Histone H3 during Early Embryogenesis. Curr Biol 2019; 29:359-366.e4. [DOI: 10.1016/j.cub.2018.12.020] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2018] [Revised: 10/29/2018] [Accepted: 12/13/2018] [Indexed: 11/27/2022]
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Horard B, Sapey-Triomphe L, Bonnefoy E, Loppin B. ASF1 is required to load histones on the HIRA complex in preparation of paternal chromatin assembly at fertilization. Epigenetics Chromatin 2018; 11:19. [PMID: 29751847 PMCID: PMC5946387 DOI: 10.1186/s13072-018-0189-x] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2018] [Accepted: 04/24/2018] [Indexed: 12/15/2022] Open
Abstract
Background Anti-Silencing Factor 1 (ASF1) is a conserved H3–H4 histone chaperone involved in both Replication-Coupled and Replication-Independent (RI) nucleosome assembly pathways. At DNA replication forks, ASF1 plays an important role in regulating the supply of H3.1/2 and H4 to the CAF-1 chromatin assembly complex. ASF1 also provides H3.3–H4 dimers to HIRA and DAXX chaperones for RI nucleosome assembly. The early Drosophila embryo is an attractive system to study chromatin assembly in a developmental context. The formation of a diploid zygote begins with the unique, genome-wide RI assembly of paternal chromatin following sperm protamine eviction. Then, within the same cytoplasm, syncytial embryonic nuclei undergo a series of rapid, synchronous S and M phases to form the blastoderm embryo. Here, we have investigated the implication of ASF1 in these two distinct assembly processes. Results We show that depletion of the maternal pool of ASF1 with a specific shRNA induces a fully penetrant, maternal effect embryo lethal phenotype. Unexpectedly, despite the depletion of ASF1 protein to undetectable levels, we show that asf1 knocked-down (KD) embryos can develop to various stages, thus demonstrating that ASF1 is not absolutely required for the amplification of cleavage nuclei. Remarkably, we found that ASF1 is required for the formation of the male pronucleus, although ASF1 protein does not reside in the decondensing sperm nucleus. In asf1 KD embryos, HIRA localizes to the male nucleus but is only capable of limited and insufficient chromatin assembly. Finally, we show that the conserved HIRA B domain, which is involved in ASF1-HIRA interaction, is dispensable for female fertility. Conclusions We conclude that ASF1 is critically required to load H3.3–H4 dimers on the HIRA complex prior to histone deposition on paternal DNA. This separation of tasks could optimize the rapid assembly of paternal chromatin within the gigantic volume of the egg cell. In contrast, ASF1 is surprisingly dispensable for the amplification of cleavage nuclei, although chromatin integrity is likely compromised in KD embryos. Electronic supplementary material The online version of this article (10.1186/s13072-018-0189-x) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Béatrice Horard
- Laboratoire de Biométrie et Biologie Evolutive - CNRS - UMR5558, Université Claude Bernard Lyon I, 16, rue R. Dubois - Bât. G. Mendel, 69622, Villeurbanne Cedex, France.
| | - Laure Sapey-Triomphe
- Laboratoire de Biométrie et Biologie Evolutive - CNRS - UMR5558, Université Claude Bernard Lyon I, 16, rue R. Dubois - Bât. G. Mendel, 69622, Villeurbanne Cedex, France
| | - Emilie Bonnefoy
- Laboratoire de Biométrie et Biologie Evolutive - CNRS - UMR5558, Université Claude Bernard Lyon I, 16, rue R. Dubois - Bât. G. Mendel, 69622, Villeurbanne Cedex, France
| | - Benjamin Loppin
- Laboratoire de Biométrie et Biologie Evolutive - CNRS - UMR5558, Université Claude Bernard Lyon I, 16, rue R. Dubois - Bât. G. Mendel, 69622, Villeurbanne Cedex, France.
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10
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Flora P, McCarthy A, Upadhyay M, Rangan P. Role of Chromatin Modifications in Drosophila Germline Stem Cell Differentiation. Results Probl Cell Differ 2017; 59:1-30. [PMID: 28247044 DOI: 10.1007/978-3-319-44820-6_1] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
During Drosophila oogenesis, germline stem cells (GSCs) self-renew and differentiate to give rise to a mature egg. Self-renewal and differentiation of GSCs are regulated by both intrinsic mechanisms such as regulation of gene expression in the germ line and extrinsic signaling pathways from the surrounding somatic niche. Epigenetic mechanisms, including histone-modifying proteins, nucleosome remodeling complexes, and histone variants, play a critical role in regulating intrinsic gene expression and extrinsic signaling cues from the somatic niche. In the GSCs, intrinsic epigenetic modifiers are required to maintain a stem cell fate by promoting expression of self-renewal factors and repressing the differentiation program. Subsequently, in the GSC daughters, epigenetic regulators activate the differentiation program to promote GSC differentiation. During differentiation, the GSC daughter undergoes meiosis to give rise to the developing egg, containing a compacted chromatin architecture called the karyosome. Epigenetic modifiers control the attachment of chromosomes to the nuclear lamina to aid in meiotic recombination and the release from the lamina for karyosome formation. The germ line is in close contact with the soma for the entirety of this developmental process. This proximity facilitates signaling from the somatic niche to the developing germ line. Epigenetic modifiers play a critical role in the somatic niche, modulating signaling pathways in order to coordinate the transition of GSC to an egg. Together, intrinsic and extrinsic epigenetic mechanisms modulate this exquisitely balanced program.
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Affiliation(s)
- Pooja Flora
- Department of Biological Sciences/RNA Institute, University at Albany SUNY, Albany, NY, USA
- University at Albany SUNY, 1400 Washington Avenue, Albany, NY, 12222, USA
| | - Alicia McCarthy
- Department of Biological Sciences/RNA Institute, University at Albany SUNY, Albany, NY, USA
- University at Albany SUNY, 1400 Washington Avenue, Albany, NY, 12222, USA
| | - Maitreyi Upadhyay
- Department of Biological Sciences/RNA Institute, University at Albany SUNY, Albany, NY, USA
- University at Albany SUNY, 1400 Washington Avenue, Albany, NY, 12222, USA
| | - Prashanth Rangan
- Department of Biological Sciences/RNA Institute, University at Albany SUNY, Albany, NY, USA.
- University at Albany SUNY, 1400 Washington Avenue, Albany, NY, 12222, USA.
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Yuan K, Seller CA, Shermoen AW, O'Farrell PH. Timing the Drosophila Mid-Blastula Transition: A Cell Cycle-Centered View. Trends Genet 2016; 32:496-507. [PMID: 27339317 DOI: 10.1016/j.tig.2016.05.006] [Citation(s) in RCA: 54] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2016] [Revised: 05/19/2016] [Accepted: 05/23/2016] [Indexed: 11/18/2022]
Abstract
At the mid-blastula transition (MBT), externally developing embryos refocus from increasing cell number to elaboration of the body plan. Studies in Drosophila reveal a sequence of changes in regulators of Cyclin:Cdk1 that increasingly restricts the activity of this cell cycle kinase to slow cell cycles during early embryogenesis. By reviewing these events, we provide an outline of the mechanisms slowing the cell cycle at and around the time of MBT. The perspectives developed should provide a guiding paradigm for the study of other MBT changes as the embryo transits from maternal control to a regulatory program centered on the expression of zygotic genes.
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Affiliation(s)
- Kai Yuan
- Department of Biophysics and Biochemistry, University of California San Francisco (UCSF), San Francisco, CA 94158, USA
| | - Charles A Seller
- Department of Biophysics and Biochemistry, University of California San Francisco (UCSF), San Francisco, CA 94158, USA
| | - Antony W Shermoen
- Department of Biophysics and Biochemistry, University of California San Francisco (UCSF), San Francisco, CA 94158, USA
| | - Patrick H O'Farrell
- Department of Biophysics and Biochemistry, University of California San Francisco (UCSF), San Francisco, CA 94158, USA.
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Abstract
The union of haploid gametes at fertilization initiates the formation of the diploid zygote in sexually reproducing animals. This founding event of embryogenesis includes several fascinating cellular and nuclear processes, such as sperm-egg cellular interactions, sperm chromatin remodelling, centrosome formation or pronuclear migration. In comparison with other aspects of development, the exploration of animal fertilization at the functional level has remained so far relatively limited, even in classical model organisms. Here, we have reviewed our current knowledge of fertilization in Drosophila melanogaster, with a special emphasis on the genes involved in the complex transformation of the fertilizing sperm nucleus into a replicated set of paternal chromosomes.
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Affiliation(s)
- Benjamin Loppin
- Laboratoire de Biométrie et Biologie Evolutive, CNRS UMR5558, Université Claude Bernard Lyon 1, Villeurbanne, France
| | - Raphaëlle Dubruille
- Laboratoire de Biométrie et Biologie Evolutive, CNRS UMR5558, Université Claude Bernard Lyon 1, Villeurbanne, France
| | - Béatrice Horard
- Laboratoire de Biométrie et Biologie Evolutive, CNRS UMR5558, Université Claude Bernard Lyon 1, Villeurbanne, France
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Abstract
Lipid droplets are the intracellular sites for neutral lipid storage. They are critical for lipid metabolism and energy homeostasis, and their dysfunction has been linked to many diseases. Accumulating evidence suggests that the roles lipid droplets play in biology are significantly broader than previously anticipated. Lipid droplets are the source of molecules important in the nucleus: they can sequester transcription factors and chromatin components and generate the lipid ligands for certain nuclear receptors. Lipid droplets have also emerged as important nodes for fatty acid trafficking, both inside the cell and between cells. In immunity, new roles for droplets, not directly linked to lipid metabolism, have been uncovered, with evidence that they act as assembly platforms for specific viruses and as reservoirs for proteins that fight intracellular pathogens. Until recently, knowledge about droplets in the nervous system has been minimal, but now there are multiple links between lipid droplets and neurodegeneration: many candidate genes for hereditary spastic paraplegia also have central roles in lipid-droplet formation and maintenance, and mitochondrial dysfunction in neurons can lead to transient accumulation of lipid droplets in neighboring glial cells, an event that may, in turn, contribute to neuronal damage. As the cell biology and biochemistry of lipid droplets become increasingly well understood, the next few years should yield many new mechanistic insights into these novel functions of lipid droplets.
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Histone H1: Lessons from Drosophila. BIOCHIMICA ET BIOPHYSICA ACTA-GENE REGULATORY MECHANISMS 2015; 1859:526-32. [PMID: 26361208 DOI: 10.1016/j.bbagrm.2015.09.001] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/16/2015] [Revised: 08/28/2015] [Accepted: 09/02/2015] [Indexed: 01/02/2023]
Abstract
Eukaryotic genomes are structured in the form of chromatin with the help of a set of five small basic proteins, the histones. Four of them are highly conserved through evolution, form the basic unit of the chromatin, the nucleosome, and have been intensively studied and are well characterized. The fifth histone, histone H1, adds to this basic structure through its interaction at the entry/exit site of DNA in the nucleosome and makes an essential contribution to the higher order folding of the chromatin fiber. Histone H1 is the less conserved histone and the less known of them. Though for long time considered as a general repressor of gene expression, recent studies in Drosophila have rejected this view and have contributed to uncover important functions on genome stability and development. Here we present some of the most recent data obtained in the Drosophila model system and discuss how the lessons learnt in these studies compare and could be applied to all other eukaryotes.
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