Academic literature on the topic 'Variantes H1'

At least eleven histone H1 variants exist in mammalian somatic cells that bind to the linker DNA and stabilize the nucleosome particle contributing to higher order chromatin compaction. In addition of playing a structural role, H1 seems to be involved in the activation and repression of gene expression. It is not well known whether the different variants have specific roles or regulate specific promoters. We have explored this by inducible shRNA-mediated knock-down of each of the H1 variants in a human breast cancer cell line. Rapid inhibition of each H1 variant was not compensated by changes of expression of other variants. A different, reduced subset of genes is altered in each H1 knock-down. Interestingly, H1.2 depletion represses expression of a number of cell cycle genes. This is concomitant with a G1 arrest phenotype observed in this cell line. In addition, H1.2 depletion caused decreased global nucleosome spacing. These effects are specific of H1.2 depletion as they are not complemented by overexpression of other variants and they do not occur in knock-downs for the other variants. Moreover, H1.4 depletion caused cell death in T47D, being the first report of the essentiality of an H1 variant for survival in a human cell type. In addition to this, we have also investigated specificities of H1 subtypes location in particular promoters of interest in our laboratory, as well as specific interactions with other factors by generating HA-tagged H1 variant expressing cell lines.<br>Al menos once variantes de la histona H1 han sido identificadas en mamíferos, todas ellas se unen al ADN entre nucleosomas contribuyendo así, a la estabilización de la partícula nucleosómica y a la compactación de la cromatina en estructuras de alto orden. Además de jugar un papel estructural, H1 parece estar implicada en la activación y represión de la expresión génica. Se desconoce si las diferentes variantes de H1 tienen funciones específicas o regulan promotores específicos. Con el objetivo de investigar esta hipótesis se han generado líneas celulares que inhiben de forma inducible, mediante la tecnología de ARN interferente, la expresión de cada una de las variantes de forma específica. La inhibición de cada una de las variantes no es compensada por cambios en la expresión del resto de subtipos. Distintos grupos de genes resultan alterados con la depleción de cada una de las variantes de H1. La inhibición de H1.2 reprime la expresión de una serie de genes de ciclo celular, correlacionando con un fenotipo de arresto celular en fase G1 observado en esta línea. Además, la inhibición de H1.2 causa una disminución global del espaciamiento entre nucleosomas. Todos estos efectos parecen ser específicos para la falta de H1.2 ya que no son complementados por la sobreexpresión de otras variantes. Por otro lado, la inhibición de H1.4 causa muerte celular en T47D. Ésta es la primera vez que se describe que una variante de H1 es esencial para la supervivencia de una línea celular humana.<br/>En un segundo plano, se han construido líneas celulares con expresión de las variantes de H1 fusionadas al péptido HA, con el objetivo de estudiar la especificidad de su localización en promotores de interés para el grupo, así como interacciones específicas con otros factores celulares.

Seven linker histone H1 variants are present in human somatic cells with distinct prevalence across cell types. Using variant-specific antibodies to H1 and hemagglutinin-tagged recombinant H1 variants expressed in breast cancer cells, their genomic distribution was assessed. Specifically, ChIP-Seq data was obtained for two replication-dependent (H1.2 and H1.4) and replication-independent H1 variants (H1.0 and H1X) together with core histone H3. Briefly, we have previously reported that H1.2 is the H1 variant that better correlates with gene repression. It was found enriched at GC-poor, gene-poor and intergenic chromosomal domains in addition to lamin-associated domains (LADs). We further explored linker histone H1 variant distribution and strikingly, we found that distribution of replication-independent H1 variants (H1.0 and H1X) is distinct. H1.0 was found enriched at nucleolar features such as nucleolus-associated domains (NADs), nucleolus organizer regions (NORs) encoding for the 45S rDNA, specifically at non-transcribed spacers and also in 5S rDNA. Specific repetitive sequences such as SINE-VNTR-Alu (SVA) retrotransposons and telomeric and ACRO1 satellites showed also a specific enrichment of H1.0. On the other hand, H1X has been associated to actively transcribed chromatin indicated by a colocalization with RNAPII-enriched regions and an enrichment towards the 3’ end of active genes. In addition, constitutive exons, included alternatively spliced exons and retained introns are enriched in H1X. Further, specific non-coding RNA (miRNA and snoRNA), mainly found at introns showed a H1X enrichment. Our results point to a potential role of H1X in elongation, splicing or non-coding RNA regulation, which might be prompting gene transcription without changes in core histone post-translational modifications. Furthermore, depletion of multiple H1 variants (H1.2 and H1.4) triggers an interferon response due to an aberrant transcription of repetitive elements in breast cancer cells. Transcription of repetitive elements was observed by an increase in their RNA levels (RT-qPCR), increase in cytoplasmic dsRNA (immunofluorescence) and transcription of intergenic regions (RNA-Seq). Variants H1.2 and H1.4 seem to be critical in the observed phenotype but rescue experiments showed redundant functions for H1 variants. The molecular mechanism that leads to transcription of repetitive elements upon multiH1 KD, as happens for DE genes upon single or multiple H1 variants KD, is still unsolved. We were able to show an increase in nucleosome accessibility genome-wide (ATAC-Seq) that did not fully correlate with the observed transcriptional changes in multiple H1 depleted cells. Surprisingly, post-translational modifications of core histone remained unchanged as happens for single H1X depletion. Specific molecular mechanisms, involved in transcriptional modulation, that might be regulated by a particular H1 variant (or H1 variant combinations) are appealing possibilities. Among them, establishment, maintenance or organization of nuclear domains (lamin-, nucleolus- or topologically associated domains), chromosome structures (centromeres) or localised heterochromatin regions (transposons). Beyond promoters where histone H1 content clearly correlate with repression, other transcription-related processes might be regulated by specific H1 variants. Processes influenced by RNAPII (elongation or splicing) and other regulatory elements (non-coding RNAs or enhancers) need to be certainly explored in a histone H1 variant(s) depletion context. Upon single and multiple H1 variants depletion, H1.0 is induced in a regulated manner that may depend in histone acetylation, assessed by ChIP-qPCR at promoter regions and by treatments with histone deacetylase inhibitor (TSA). Further experiments are needed to elucidate relocation of histone replication-independent H1 variants, mainly H1.0 upon changing H1 stoichiometry and during differentiation, reprogramming and cancer.<br>xisten siete variantes de histona H1 presentes en células somáticas humanas con una prevalencia diferente según el tipo celular. Usando anticuerpos específicos contra las variantes de H1 y variantes de H1 recombinantes etiquetadas con hemaglutinina, evaluamos su distribución genómica en células de cáncer de mama. Concretamente, obtuvimos datos de ChIP-Seq de dos variantes de H1 dependientes de replicación (H1.2 y H1.4) y las dos variantes independientes de replicación (H1.0 y H1X). Anteriormente, observamos que H1.2 es la variante que mejor correlaciona con la represión génica y se encuentra enriquecida en dominios cromosómicos pobre en GC, pobres en genes e intergénicos, además de en los dominios asociados a lamin. Después exploramos con más profundidad la distribución de las variantes de H1 independientes de replicación. H1.0 se encontraba enriquecida en regiones asociadas al nucléolo como los dominios asociados al nucléolo, las regiones organizadoras del nucléolo que codifican para el ARN ribosomal 45S, específicamente en las regiones espaciadoras no transcritas y, también, en el 5S DNA ribosomal. Elementos repetitivos como los retrotransposones SINE-SVA-Alu y los satélites teloméricos y ACRO1 también mostraron un enriquecimiento específico de H1.0. Por otro lado, encontramos H1X asociada a cromatina activa transcripcionalmente, demostrado por una colocalización con regiones asociadas a RNAPII y un enriquecimiento hacia el extremo 3’ de genes activos. Además, todas las regiones codificantes que se incluyen en el transcrito final (exones constitutivos, exones incluidos alternativamente e intrones retenidos) mostraron un enriquecimiento en H1X. Algunas especies de ARN no codificante (miRNA y snoRNA), que se encuentran principalmente en intrones, estaban enriquecidas en H1X. Nuestros resultados apuntan a que H1X puede tener un papel en la regulación de la elongación, splicing o el ARN no codificante, que podría estar induciendo la transcripción de genes sin cambios en las modificaciones post-traduccionales de histonas. La depleción de varias variantes de H1 (H1.2 y H1.4) desencadena una respuesta de interferón debido a una transcripción aberrante de elementos repetitivos en cáncer de mama. La transcripción de elementos repetitivos se observó por un aumento de sus niveles de ARN, un aumento de los ARN de doble cadena en el citoplasma y por la transcripción de regiones intergénicas. El mecanismo molecular que conduce a su transcripción, tal como sucede con los genes desregulados en células deplecionadas de una sola variante, aún no está resuelto. Mostramos un aumento global en la accesibilidad a la cromatina que no correlaciona completamente con los cambios transcripcionales observados al deplecionar múltiples variantes de H1. Sorprendentemente, las modificaciones post-traduccionales de las histonas se mantienen intactas.

Linker histone H1 associates with nucleosomes, facilitating folding and packaging of DNA into higher order chromatin structure. With 11 variants in mammals, histone H1 is the most divergent histone class. Histone H1 variants are differentially expressed during development and cellular differentiation, and regulate specific gene expression in vivo. Ample studies have established the role of linker histone H1 in chromatin compaction and gene expression regulation; however, its role in diseases, such as cancer, remain understudied. In this study, we explore the role of H1 in ovarian cancer, one of the most devastating gynecological cancers due to its poor prognosis and difficulty in early diagnosis. Although mutations of genes responsible for cell proliferation, differentiation and survival have been found in ovarian cancers, ample evidence also suggests an important role of epigenetic changes in the disease occurrence and progression. Because epigenetic changes do not alter DNA sequence and can be reversed or reprogrammed, they offer an attractive avenue for therapeutic intervention in cancer treatment. Using quantitative RT-PCR assays, we systematically examined the expression of 7 H1 genes in 33 human epithelial ovarian tumors. By clustering analysis, we found that ovarian malignant adenocarcinomas and benign adenomas exhibited characteristic expression patterns. We demonstrate that expression profiling of 7 H1 genes in tumor samples discriminates adenocarcinomas vs. adenomas with high accuracy. These findings indicate that the expression of H1 variants is exquisitely regulated and may serve as potential epigenetic biomarkers for ovarian cancer. To further investigate the role of H1 subtypes in ovarian cancer cells, we employ an over-expression approach to test the function of H1 subtypes in an ovarian cancer cell line OVCAR-3. We found that histone H1.3 over-expression significantly suppresses the growth and colony formation of OVCAR-3 cells. Gene expression arrays identified many genes affected by H1.3 over-expression, and oncogene H19 is among the genes most dramatically repressed by H1.3 over-expression. Over-expression of several other H1 subtypes does not lead to significant reduction of H19 expression, suggesting a specific effect by H1.3. Consistently, knockdown of H1.3 increases H19 expression. Furthermore, increased expression of H1.3 leads to accumulation of H1.3 as well as increased DNA methylation at the regulatory regions of H19. Finally we identified a synergistic effect of H1.3 over-expression and H19 knockdown on inhibition of ovarian cancer cell growth. These results establish oncogene H19 as a direct target of histone H1.3, identify a novel role of H1 variants in ovarian cancer mediated through regulating oncogene H19 expression, and may offer new approaches for ovarian cancer therapeutics.

Les plantes sont caractérisées par une remarquable plasticité développementale. En vertu de leur mode de vie sessile, elles sont capables d'adaptations phénotypiques rapides en réponse à des signaux environnementaux. En particulier, les plantes ont la capacité de détecter les conditions de lumière par de multiples photorécepteurs et utilisent cette information pour adapter leur morphologie et leur physiologie à un environnement changeant. Par exemple, la première perception de la lumière par des jeunes plantules, émergeant du sol, induit des changements profonds dans l'expression des gènes qui lancent la croissance et l'activité photosynthétique. Au cours de cette transition, la reprogrammation de l'expression du génome s'accompagne de réorganisations massives de l'organisation de la chromatine dans la grande majorité des cellules des feuilles embryonnaires, les cotylédons. Ainsi, chez la plante Arabidopsis thaliana, le dé-étiolement des cotylédons est associé à une condensation rapide des principaux domaines hétérochromatiniens en 8 à 10 "chromocentres" qui se forment autour des centromères. L’étude des voies de signalisation contrôlant ce processus nous a conduit à l'identification d’un acteur moléculaire clé pour la dynamique d'organisation des chromocentres en réponse à la lumière, les histones H1. Ces histones de liaison inter-nucléosomiques sont des composants structurels conservés qui contribuent à réguler l'organisation et la condensation locale et a grande échelle de la chromatine en limitant l'accessibilité à l'ADN pour de nombreux facteurs telles que les ARN polymérases. Cette thèse porte sur la caractérisation des réarrangements chromatiniens médiés par des variants d'histone H1. Des approches cytologiques et génomiques ont permis d’appréhender l'influence des trois différents variants H1 d'Arabidopsis thaliana dans la définition des structures 3D du génome et de la chromatine des cellules de cotylédons. La combinaison de tests d’accessibilité à la transposase Tn5 (ATAC) et de capture de conformation chromosomique (Hi-C) permet également de disséquer comment les histone H1 impactent la topologie du génome et l'adaptation du paysage chromatinien pour un nouveau programme de transcription. L'analyse de l'abondance et le profilage par immuno-précipitation quantitative de marques d'histones (ChIP-Rx) a également permis d'identifier le rôle joué par les histones H1 sur le paysage chromatinien répressif ainsi que son impact fonctionnel sur de nombreux gènes et éléments répétés du génome, potentiellement en restreignant l'accès à des facteurs de transcription sur des motifs de séquence spécifiques. Collectivement, ce travail a permis de disséquer les spécificités et les redondances fonctionnelles des variants d'histones de liaison en tant que régulateurs moléculaires du paysage chromatinien chez les plantes<br>Being capable of rapid phenotypic adaptations in response to environmental cues, plants are characterized by a remarkable developmental plasticity. Specifically, plants have the ability to sense light conditions by multiple photosensory receptors and to use this crucial information to adapt their morphology and physiology to a changing environment. For example, the first perception of light by young plantlets emerging from the soil induces deep changes in gene expression that launch growth and photosynthetic activity. During this transition, genome expression reprogramming is accompanied by massive rearrangements of chromatin sub-nuclear organization. In the Arabidopsis thaliana plant species, a large part of heterochromatin containing silent and condensed repeated elements is scattered within multiple foci in the nucleoplasm of most cotyledon cells when grown in darkness. Upon exposure to light, cotyledon de-etiolation triggers the rapid condensation of heterochromatic domains into 8-to-10 large chromocenters that form around centromeres. This phenomenology has led us to the identification of histone H1 variants as key molecular players in triggering chromocenter dynamics. These inter-nucleosomal linker histones are conserved structural components of eukaryotic chromatin that contribute to both local and higher-order chromatin organization and condensation, notably restricting DNA accessibility to multiple factors such as RNA polymerases. In this thesis cytological and genomic approaches were used to investigate the influence of the three Arabidopsis thaliana H1 variants in the definition of the genome and the 3D chromatin structure in cotyledon cells. The combination of Assay for Transposase-Accessible Chromatin (ATAC) and Chromosome Conformation Capture (Hi-C) allowed dissecting how H1 histones impact genome topology and the adaptation of the chromatin landscape for a new transcriptional program. The analysis of histone marks abundance and their genome-wide profiling using quantitative chromatin immunoprecipitation (ChIP-Rx) further enhances current knowledge. We uncovered the functional impact of histones H1 in defining chromatin repressive landscape on many genes and repeated elements, potentially by restricting access to transcription factors on specific sequence motifs. Collectively, this work has allowed deciphering the specific and redundant functional implications of histone H1 variants as key molecular regulators of the chromatin landscape in plants

En los metazoos existen múltiples variantes de histona H1, siendo algunas de ellas específicas de la línea germinal y la embriogénesis temprana. Las variantes embrionarias están presentes mientras el genoma del zigoto está transcripcionalmente inactivo y posteriormente son reemplazadas por las variantes de H1 somáticas. En el caso de Drosophila, la reducción de los niveles de la variante embrionaria, dBigH1, tiene como resultado la activación prematura del genoma zigótico, lo que sugiere una posible implicación de dBigH1 en la represión del genoma. Durante el desarrollo de esta tesis doctoral hemos utilizado células S2 de Drosophila, que no expresan dBigH1, para caracterizar los efectos diferenciales de dBigH1 sobre la transcripción en comparación con la variante somática, dH1. Hemos visto que cuando expresamos dBigH1 en células S2 se incorpora a la cromatina uniformemente y, además, reemplaza la dH1. La expresión de dBigH1 en estas células, además, regula negativamente la transcripción. Esta regulación negativa se debe a que dBigH1 interfiere en la unión de la RNA polimerasa II y en la acetilación de las histonas. Por otro lado, en este trabajo también hemos estudiado la función de los diferentes dominios de dBigH1 y hemos encontrado que el dominio C-terminal es necesario para su unión a la cromatina. En cambio, la región N-terminal contiene una región rica en residuos ácidos, llamada dominio ED, que es el responsable del reemplazo de dH1 y la represión de la transcripción ya que cuando expresamos una forma truncada de la proteína que no contiene el dominio ED, dBigH1 no interfiere en la unión de la RNA polimerasa II y la acetilación de las histonas. Además, dBigH1 está presente en la línea germinal femenina. dBigH1 se expresa en las células madre germinales y en sus hijas, los cistoblastos. Posteriormente desaparece en la región de divisiones mitóticas y se vuelve a expresar en las cámaras ováricas. A medida que se desarrollan las cámaras ováricas, la expresión de dBigH1 queda restringida al oocito. Además, en la línea germinal femenina encontramos dH1, que coexiste con dBigH1 en las células madre germinales, cistoblastos y, durante los primeros estadios del desarrollo de las cámaras ováricas, el oocito. En este trabajo hemos visto que las células que contienen ambas variantes son activas transcripcionalmente. Sin embargo, cuando el genoma del oocito está totalmente silenciado únicamente encontramos dBigH1, a excepción de los estadios 8-11, en los que dBigH1 permite la reanudación de la actividad transcripcional. En este trabajo también hemos estudiado la regulación de la expresión de dBigH1 en la línea germinal femenina y hemos encontrado que está regulada postranscripcionalmente mediante señales localizadas en la región 3’UTR del mRNA. Finalmente, hemos encontrado que uno de los responsables de la regulación de dBigH1 es Brat, probablemente de manera directa a través de la unión al 3’UTR del mRNA de dBigH1.<br>Linker histones H1 are one of the main components of chromatin. Histone H1 is a highly heterogeneous family of proteins and several variants have been described in metazoa. Some of them are specifically expressed in the germline and are retained in the early embryo. However, in Drosophila, only one somatic H1, dH1, and one embryonic and germline-specific variant, dBigH1, have been described. dBigH1 is present during early embriogenesis, when the zygotic genome is silenced and is replaced at cellularization by dH1. The reduction of dBigH1 levels results in a premature activation of the zygotic genome, suggesting a role of dBigH1 in transcriptional silencing. We report here that ectopic expression of dBigH1 in Drosophila S2 cells results in dBigH1 binding across chromatin and replacement of dH1. This binding and replacement result in down-regulation of gene expression by altering RNApol II binding and histone acetylation at promoters. We also show that the effects of dBigH1 depend on the highly acidic ED-domain of the N-terminal tail, since a truncated form lacking this domain does not replace dH1 or affect transcription. We also show that dBiH1 is present in the female germline. dBigH1 is expressed in the germ stem cells and cystoblasts, disappears in the mitotic divisions region and is expressed again in cysts cells that are surrounded by the follicular cells to form an egg chamber. As the egg chambers develop, dBigH1 expression is restricted to the oocyte. In the germline dBigH1 and dH1 coexist in germ stem cells, cystoblasts and early oocytes. However, dBigH1 is the only variant present in the oocyte when is completely silenced. We demonstrate also that in cyst cells, dBigH1 expression is postranscriptionally regulated through signals present in the mRNA 3’UTR region. Finally, we show that Brat participates in the down-regulation of dBigH1 expression, probably through a direct mechanism.

Un melange d'histone h1 extraites du foie de rat est fractionne par hplc en phase inverse. Une histone h#o et cinq sous-fractions d'histones h1-1 sont obtenues sous forme pure. La composition en acides amines est determinee; la structure est caracterisee par degradation enzymatique, renaturation in vitro, electrophorese, fluorence intrinseque

H1 linker histone facilitates the formation of higher order chromatin structure and is essential for mammalian development. Mice have 11 H1 variants which are differentially regulated and conserved in human. Previous research indicates that H1 regulates the expression of specific genes in mouse embryonic stem cells (ESCs). However, whether individual variants have distinct functions and how H1 participates in gene regulation remain elusive. An investigation of the precise localization of individual H1 variants in vivo would facilitate the elucidation of mechanisms underlying chromatin compaction regulated gene expression, while it has been extremely difficult due to the lacking of specific antibodies toward H1 variants. In this dissertation, I have generated a knock-in system in ESCs and shown that the N-terminally tagged H1 proteins are functionally interchangeable to their endogenous counterparts in vivo. H1d and H1c are depleted from GC- and gene-rich regions and active promoters, inversely correlated with H3K4me3, but positively correlated with H3K9me3 and associated with characteristic sequence features. Surprisingly, both H1d and H1c are significantly enriched at major satellites, which display increased nucleosome spacing compared with bulk chromatin. While also depleted at active promoters and enriched at major satellites, overexpressed H10 displays differential binding patterns in specific repetitive sequences compared with H1d and H1c. Depletion of H1c, H1d ,and H1e causes pericentric chromocenter clustering and de-repression of major satellites. Collectively, these results integrate the localization of an understudied type of chromatin proteins, namely the H1 variants, into the epigenome map of mouse ESCs, and demonstrate significant changes at pericentric heterochromatin upon depletion of this epigenetic mark.

Durant el desenvolupament d’aquesta tesi doctoral hem identificat i caracteritzat la variant d’histona H1 present a la línia germinal i l’embrió primerenc de Drosophila melanogaster. Els metazous contenen múltiples variants d’histona H1. Particularment, la majoria d’espècies estudiades contenen diverses variants d’histona H1 que reemplacen les H1 somàtiques a la línia germinal i als primers estadis del desenvolupament embrionari. Drosophila era l’excepció ja que, fins ara tan sols es coneixia una única histona H1, que s’expressa des de la cel·lularització de l’embrió i que perdura durant tot el cicle biològic de la mosca. En aquest treball hem identificat la histona H1 embrionària i de la línia germinal de D.melanogaster, dBigH1. dBigH1 és molt abundant durant els primers estadis embrionaris, abans de la cel·lularització de l’embrió, quan la histona H1 somàtica (dH1) és absent i el genoma zigòtic es troba silenciat. Durant la cel·lularització, quan el genoma del zigot s’activa progressivament, dH1 reemplaça dBigH1 a les cèl·lules somàtiques. Tot i això, dBigH1 es reté a les primordial germ cells (PGCs) com a mínim fins l’estadi 12. Aquestes cèl·lules donaran lloc a la línia germinal del futur organisme. En aquest treball vam generar una mutació de falta de funció de dBigH1 a la qual vam anomenar dbigH1100. Els embrions mutants dbigH1100 presenten una activació prematura del genoma zigòtic, tan a les cèl·lules somàtiques com a les PGCs. Els embrions mutants dbigH1100 moren abans de la cel·lularització i presenten un augment dels nivells de RNA Polimerasa II elongant i un augment de trànscrits zigòtics. A més a més, la letalitat va acompanyada de dany al DNA i defectes mitòtics. Aquests resultats suggereixen que dBigH1 té una funció essencial en la regulació de l’activació del genoma zigòtic durant la cel·lularització. De la mateixa forma que altres metazous, dBigH1 també es troba present a la línia germinal femenina. Tot i això, a diferència d’altres espècies estudiades, on existeixen variants d’H1 específiques de mascle, dBigH1 també es troba present a la línia germinal masculina. Tan a les gònades masculines com a les femenines, dBigH1 està expressada a les cèl·lules mare germinals (GSC), que es troben adherides a un nínxol que ajuda al seu manteniment com a cèl·lules mare. A les gònades masculines dBigH1 no està present a la regió proliferativa, on hi ha els grups d’espermatogònies, i torna a expressar-se als espermatòcits. A les gònades femenines, dBigH1 té un patró de localització similar ja que es troba absent a les oogònies proliferants, però torna a expressar-se a les cambres ovàriques. En una condició de falta de funció de dBigH1 es produeixen defectes en la gametogènesi masculina i es detecta una acumulació d’espermatogònies. En aquestes gònades es produeix un augment dels nivells de Bam, un factor de diferenciació clau en aquest procés. En una situació control, els nivells de Bam augmenten durant la fase proliferativa, però aquest gen es torna a mantenir silenciat per tal que les espermatogònies deixin de proliferar i es diferenciïn a espermatòcits. Aquests resultats suggereixen que dBigH1 té una contribució en la regulació de l’expressió de bam durant la diferenciació de les espermatogònies. A més a més, també hem mostrat que la distribució de dBigH1 al llarg de la cromatina dels espermatòcits correlaciona negativament amb l’expressió gènica. Així doncs, els gens que es troben silenciats tenen un contingut alt en dBigH1, mentre que els gens més expressats tenen un contingut menor en la proteïna. De fet, en una situació de falta de funció de dBigH1 als espermatòcits, es produeix un augment de l’expressió d’aquells gens que, en una situació control, es troben silenciats. Aquests resultats suggereixen que dBigH1 també té una contribució en la regulació de l’expressió gènica durant la gametogènesi masculina.<br>During the development of this thesis we have descrived the germline and embryonic histone H1 variant of Drosophila melanogaster. Metazoans usually contain multiple histone H1 variants. In particular, specific variants replace somatic histone H1s in the germline and early embryogenesis. In this regard, Drosophila was an exception because a single dH1 was known. During this work, we identified the embryonic histone H1 of Drosophila, dBigH1. dBigH1 is abundant during early embryogenesis before cellularization occurs, when the somatic H1 is absent and the zygotic genome is inactive. Upon cellularization, when the zygotic genome si progressively activated, dH1 replaces dBigH1 in the soma, but not in the primordial germ cells (PGCs). dBigH1 loss-of-function mutant embryos show premature zygotic genome activation, both in the soma and the PGCs. Mutant embryos die at cellularization, showing increased levels of active RNApol II and zygotic transcripts, along with DNA damage and mitotic defects. These results show an essential function of dBigH1 in zygotic genome activation regulation. Like in other metazoans, dBigH1 is present in the female germline. However, it is also present in the male germline, while other metazoans contain diferent male-specific H1s. In the gonads, dBigH1 is expressed in the germ stem cells attached to the stem cell niche, both in males and females. In male gonads it is also present in the spermatocytes and, in the female gonads, it is also present in the egg chambers. dBigH1 knock-down testis have problems in the regulation of spermatogenesis, which results in spermatogonia accumulation and a decrease in male fertility. This is due to an upregulation of bam, a key regulator of this process. These results show a dBigH1 contribution in the regulation of bam expression during gametogenesis. Moreover, we also show that dBigH1 distribution across spermatocytes chromatin negativelly correlates with gene expression. dBigH1 is accumulated in genes which must remain silenced, whereas genes highly expressed in these cells contain less dBigH1 content. In this regard, a dBigH1 knock-down condition show an upregulation of these silenced genes. These results show that dBigH1 also contributes to transcriptional regulation in the germline.