RESUMEN
PIWI-interacting small RNAs (piRNAs) establish sequence-specific adaptive restriction of resident genomic parasites to guard genome integrity. In this issue of Cell, Yu, Koppetsch, et al. describe an innate piRNA-response that specifically fragments the viral RNA genome in the germline of recently invaded koalas. This first line of defense might ensure survival until adaptive immunity develops.
Asunto(s)
Phascolarctidae , Animales , Genoma , Células Germinativas , ARN Interferente PequeñoRESUMEN
Tandem zinc finger (ZF) proteins are the largest and most rapidly diverging family of DNA-binding transcription regulators in mammals. ZFP568 represses a transcript of placental-specific insulin like growth factor 2 (Igf2-P0) in mice. ZFP568 binds a 24-base pair sequence-specific element upstream of Igf2-P0 via the eleven-ZF array. Both DNA and protein conformations deviate from the conventional one finger-three bases recognition, with individual ZFs contacting 2, 3, or 4 bases and recognizing thymine on the opposite strand. These interactions arise from a shortened minor groove caused by an AT-rich stretch, suggesting adaptability of ZF arrays to sequence variations. Despite conservation in mammals, mutations at Igf2 and ZFP568 reduce their binding affinity in chimpanzee and humans. Our studies provide important insights into the evolutionary and structural dynamics of ZF-DNA interactions that play a key role in mammalian development and evolution.
Asunto(s)
ADN/metabolismo , Proteínas Nucleares/metabolismo , Secuencia de Aminoácidos , Animales , Secuencia de Bases , Sitios de Unión , Proteínas Portadoras/química , Proteínas Portadoras/clasificación , Proteínas Portadoras/genética , Proteínas Portadoras/metabolismo , ADN/química , Humanos , Factor II del Crecimiento Similar a la Insulina/química , Factor II del Crecimiento Similar a la Insulina/genética , Factor II del Crecimiento Similar a la Insulina/metabolismo , Ratones , Simulación de Dinámica Molecular , Proteínas Nucleares/química , Proteínas Nucleares/clasificación , Proteínas Nucleares/genética , Conformación de Ácido Nucleico , Pan troglodytes , Filogenia , Polimorfismo de Nucleótido Simple , Unión Proteica , Estructura Terciaria de Proteína , Proteínas Recombinantes/biosíntesis , Proteínas Recombinantes/química , Proteínas Recombinantes/aislamiento & purificación , Alineación de SecuenciaRESUMEN
Retroviral restriction is a complex phenomenon that, despite remarkable recent progress, is far from being well understood. In this Preview, we introduce an insightful study by Yang et al. that represents the first attempt to identify the global determinants of retroviral repression in pluripotent mammalian cells.
Asunto(s)
Células Madre Embrionarias/virología , Retrovirus Endógenos/genética , Provirus/genética , AnimalesRESUMEN
Nearly half of the human genome consists of endogenous retroelements (EREs) and their genetic remnants, a small fraction of which carry the potential to propagate in the host genome, posing a threat to genome integrity and cell/organismal survival. The largest family of transcription factors in tetrapods, the Krüppel-associated box domain zinc finger proteins (KRAB-ZFPs), binds to specific EREs and represses their transcription. Since their first appearance over 400 million years ago, KRAB-ZFPs have undergone dramatic expansion and diversification in mammals, correlating with the invasions of new EREs. In this article we review our current understanding of the structure, function, and evolution of KRAB-ZFPs and discuss growing evidence that the arms race between KRAB-ZFPs and the EREs they target is a major driving force for the evolution of new traits in mammals, often accompanied by domestication of EREs themselves.
Asunto(s)
Inmunidad Celular/fisiología , Mamíferos/genética , Retroelementos , Dedos de Zinc/fisiología , Animales , Regulación de la Expresión Génica , Impresión Genómica , Interacciones Huésped-Patógeno/genética , Interacciones Huésped-Patógeno/inmunología , Meiosis , Familia de Multigenes , Dominios ProteicosRESUMEN
Transposable elements (TEs) promote genetic innovation but also threaten genome stability. Despite multiple layers of host defence, TEs actively shape mammalian-specific developmental processes, particularly during pre-implantation and extra-embryonic development and at the maternal-fetal interface. Here, we review how TEs influence mammalian genomes both directly by providing the raw material for genetic change and indirectly via co-evolving TE-binding Krüppel-associated box zinc finger proteins (KRAB-ZFPs). Throughout mammalian evolution, individual activities of ancient TEs were co-opted to enable invasive placentation that characterizes live-born mammals. By contrast, the widespread activity of evolutionarily young TEs may reflect an ongoing co-evolution that continues to impact mammalian development.
Asunto(s)
Elementos Transponibles de ADN , Mamíferos/embriología , Animales , Proteínas de Unión al ADN/metabolismo , Embrión de Mamíferos/metabolismo , Genoma , Humanos , Mamíferos/genética , Mamíferos/metabolismo , Cigoto/metabolismoRESUMEN
The placenta is an organ with extraordinary phenotypic diversity in eutherian mammals. Recent evidence suggests that numerous human placental enhancers are evolved from lineage-specific insertions of endogenous retroviruses (ERVs), yet the transcription factors (TFs) underlying their regulation remain largely elusive. Here, by first focusing on MER41, a primate-specific ERV family previously linked to placenta and innate immunity, we uncover the binding motifs of multiple crucial trophoblast TFs (GATA2/3, MSX2, GRHL2) in addition to innate immunity TFs STAT1 and IRF1. Integration of ChIP-seq data confirms the binding of GATA2/3, MSX2, and their related factors on the majority of MER41-derived enhancers in human trophoblast stem cells (TSCs). MER41-derived enhancers that are constitutively active in human TSCs are distinct from those activated upon interferon stimulation, which is determined by the binding of relevant TFs and their subfamily compositions. We further demonstrate that GATA2/3 and MSX2 have prevalent binding to numerous other ERV families - indicating their broad impact on ERV-derived enhancers. Functionally, the derepression of many syncytiotrophoblast genes after MSX2 knockdown is likely to be mediated by regulatory elements derived from ERVs - suggesting ERVs are also important for mediating transcriptional repression. Overall, this study characterizes the regulation of ERV-derived regulatory elements by GATA2/3, MSX2, and their cofactors in human TSCs, and provides mechanistic insights into the importance of ERVs in human trophoblast regulatory network.
Asunto(s)
Retrovirus Endógenos , Animales , Femenino , Humanos , Embarazo , Factor de Transcripción GATA2/genética , Mamíferos/genética , Placenta/fisiología , Primates/genética , Secuencias Reguladoras de Ácidos Nucleicos , Células Madre , TrofoblastosRESUMEN
Transcriptional enhancers enable exquisite spatiotemporal control of gene expression in metazoans. Enrichment of monomethylation of histone H3 lysine 4 (H3K4me1) is a major chromatin signature of transcriptional enhancers. Lysine (K)-specific demethylase 1A (KDM1A, also known as LSD1), an H3K4me2/me1 demethylase, inactivates stem-cell enhancers during the differentiation of mouse embryonic stem cells (mESCs). However, its role in undifferentiated mESCs remains obscure. Here, we show that KDM1A actively maintains the optimal enhancer status in both undifferentiated and lineage-committed cells. KDM1A occupies a majority of enhancers in undifferentiated mESCs. KDM1A levels at enhancers exhibit clear positive correlations with its substrate H3K4me2, H3K27ac, and transcription at enhancers. In Kdm1a-deficient mESCs, a large fraction of these enhancers gains additional H3K4 methylation, which is accompanied by increases in H3K27 acetylation and increased expression of both enhancer RNAs (eRNAs) and target genes. In postmitotic neurons, loss of KDM1A leads to premature activation of neuronal activity-dependent enhancers and genes. Taken together, these results suggest that KDM1A is a versatile regulator of enhancers and acts as a rheostat to maintain optimal enhancer activity by counterbalancing H3K4 methylation at enhancers.
RESUMEN
The life cycle of endogenous retroviruses (ERVs), also called long terminal repeat (LTR) retrotransposons, begins with transcription by RNA polymerase II followed by reverse transcription and re-integration into the host genome. While most ERVs are relics of ancient integration events, "young" proviruses competent for retrotransposition-found in many mammals, but not humans-represent an ongoing threat to host fitness. As a consequence, several restriction pathways have evolved to suppress their activity at both transcriptional and post-transcriptional stages of the viral life cycle. Nevertheless, accumulating evidence has revealed that LTR sequences derived from distantly related ERVs have been exapted as regulatory sequences for many host genes in a wide range of cell types throughout mammalian evolution. Here, we focus on emerging themes from recent studies cataloging the diversity of ERV LTRs acting as important transcriptional regulatory elements in mammals and explore the molecular features that likely account for LTR exaptation in developmental and tissue-specific gene regulation.
Asunto(s)
ADN Viral/genética , Retrovirus Endógenos/genética , Regulación Viral de la Expresión Génica , Secuencias Repetidas Terminales , Transcripción Genética , Replicación Viral , Animales , Ensamble y Desensamble de Cromatina , Replicación del ADN , ADN Viral/biosíntesis , ADN Viral/química , Retrovirus Endógenos/crecimiento & desarrollo , Retrovirus Endógenos/metabolismo , Interacciones Huésped-Patógeno , Humanos , Regiones Promotoras Genéticas , ARN Polimerasa II/genética , ARN Polimerasa II/metabolismo , ARN Largo no Codificante/biosíntesis , ARN Largo no Codificante/genética , ADN Polimerasa Dirigida por ARN/metabolismoRESUMEN
Most transposable elements (TEs) in the mouse genome are heavily modified by DNA methylation and repressive histone modifications. However, a subset of TEs exhibit variable methylation levels in genetically identical individuals, and this is associated with epigenetically conferred phenotypic differences, environmental adaptability, and transgenerational epigenetic inheritance. The evolutionary origins and molecular mechanisms underlying interindividual epigenetic variability remain unknown. Using a repertoire of murine variably methylated intracisternal A-particle (VM-IAP) epialleles as a model, we demonstrate that variable DNA methylation states at TEs are highly susceptible to genetic background effects. Taking a classical genetics approach coupled with genome-wide analysis, we harness these effects and identify a cluster of KRAB zinc finger protein (KZFP) genes that modifies VM-IAPs in trans in a sequence-specific manner. Deletion of the cluster results in decreased DNA methylation levels and altered histone modifications at the targeted VM-IAPs. In some cases, these effects are accompanied by dysregulation of neighboring genes. We find that VM-IAPs cluster together phylogenetically and that this is linked to differential KZFP binding, suggestive of an ongoing evolutionary arms race between TEs and this large family of epigenetic regulators. These findings indicate that KZFP divergence and concomitant evolution of DNA binding capabilities are mechanistically linked to methylation variability in mammals, with implications for phenotypic variation and putative paradigms of mammalian epigenetic inheritance.
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Metilación de ADN/genética , Mamíferos/genética , Dedos de Zinc , Animales , Cromatina/metabolismo , Cromosomas de los Mamíferos/genética , Ratones Endogámicos C57BL , Especificidad de la Especie , Transcripción Genética , Cigoto/metabolismoRESUMEN
Retroviruses have been invading mammalian germlines for millions of years, accumulating in the form of endogenous retroviruses (ERVs) that account for nearly one-tenth of the mouse and human genomes. ERVs are epigenetically silenced during development, yet the cellular factors recognizing ERVs in a sequence-specific manner remain elusive. Here we demonstrate that ZFP809, a member of the Krüppel-associated box zinc finger protein (KRAB-ZFP) family, initiates the silencing of ERVs in a sequence-specific manner via recruitment of heterochromatin-inducing complexes. ZFP809 knockout mice display highly elevated levels of ZFP809-targeted ERVs in somatic tissues. ERV reactivation is accompanied by an epigenetic shift from repressive to active histone modifications but only slight destabilization of DNA methylation. Importantly, using conditional alleles and rescue experiments, we demonstrate that ZFP809 is required to initiate ERV silencing during embryonic development but becomes largely dispensable in somatic tissues. Finally, we show that the DNA-binding specificity of ZFP809 is evolutionarily conserved in the Muroidea superfamily of rodents and predates the endogenization of retroviruses presently targeted by ZFP809 in Mus musculus. In sum, these data provide compelling evidence that ZFP809 evolved to recognize foreign DNA and establish histone modification-based epigenetic silencing of ERVs.
Asunto(s)
Proteínas de Unión al ADN/metabolismo , Retrovirus Endógenos/genética , Epigénesis Genética , Silenciador del Gen , Animales , Sitios de Unión , Proteínas de Unión al ADN/genética , Embrión de Mamíferos , Retrovirus Endógenos/fisiología , Genoma , Histonas/metabolismo , Ratones , Ratones Noqueados , Unión Proteica , Activación Viral/genética , Integración Viral/genéticaRESUMEN
In mammals, the placenta mediates maternal-fetal nutrient and waste exchange and acts in an immunomodulatory way to facilitate maternal-fetal tolerance. The placenta is highly diverse across mammalian species, yet the molecular mechanisms that distinguish the placenta of human from other mammals are not fully understood. Using an interspecies transcriptomic comparison of human, macaque, and mouse late-gestation placentae, we identified hundreds of genes with lineage-specific expression-including dozens that are placentally enriched and potentially related to pregnancy. We further annotated the enhancers for different human tissues using epigenomic data and demonstrate that the placenta and chorion are unique in that their enhancers display the least conservation. We identified numerous lineage-specific human placental enhancers and found they highly overlap with specific families of endogenous retroviruses (ERVs), including MER21A, MER41A/B, and MER39B that were previously linked to immune response and placental function. Among these ERV families, we further demonstrate that MER41A/B insertions create dozens of lineage-specific serum response factor-binding loci in human, including one adjacent to FBN2, a placenta-specific gene with increased expression in humans that produces the peptide hormone placensin to stimulate glucose secretion and trophoblast invasion. Overall, our results demonstrate the prevalence of lineage-specific placental enhancers which are frequently associated with ERV insertions and likely facilitate the lineage-specific evolution of the mammalian placenta.
Asunto(s)
Retrovirus Endógenos , Animales , Retrovirus Endógenos/genética , Femenino , Ratones , Placenta/metabolismo , Embarazo , Primates/genética , Roedores/genética , TrofoblastosRESUMEN
Global epigenetic reprogramming is vital to purge germ cell-specific epigenetic features to establish the totipotent state of the embryo. This process transpires to be carefully regulated and is not an undirected, radical erasure of parental epigenomes. The TRIM28 complex has been shown to be crucial in embryonic epigenetic reprogramming by regionally opposing DNA demethylation to preserve vital parental information to be inherited from germline to soma. Yet the DNA-binding factors guiding this complex to specific targets are largely unknown. Here, we uncover and characterize a novel, maternally expressed, TRIM28-interacting KRAB zinc-finger protein: ZFP708. It recruits the repressive TRIM28 complex to RMER19B retrotransposons to evoke regional heterochromatin formation. ZFP708 binding to these hitherto unknown TRIM28 targets is DNA methylation and H3K9me3 independent. ZFP708 mutant mice are viable and fertile, yet embryos fail to inherit and maintain DNA methylation at ZFP708 target sites. This can result in activation of RMER19B-adjacent genes, while ectopic expression of ZFP708 results in transcriptional repression. Finally, we describe the evolutionary conservation of ZFP708 in mice and rats, which is linked to the conserved presence of the targeted RMER19B retrotransposons in these species.
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Represión Epigenética , Proteínas Represoras/metabolismo , Retroelementos/genética , Dedos de Zinc , Animales , Secuencia de Bases , Sitios de Unión/genética , Blastocisto/metabolismo , Metilación de ADN/genética , Embrión de Mamíferos/metabolismo , Evolución Molecular , Ratones , Ratones Noqueados , Células Madre Embrionarias de Ratones/metabolismo , Unión Proteica/genética , Ratas , Transcripción Genética , Proteína 28 que Contiene Motivos Tripartito/metabolismoRESUMEN
Pregnancy and parturition are intricately regulated to ensure successful reproductive outcomes. However, the factors that control gestational length in humans and other anthropoid primates remain poorly defined. Here, we show the endogenous retroviral long terminal repeat transposon-like human element 1B (THE1B) selectively controls placental expression of corticotropin-releasing hormone (CRH) that, in turn, influences gestational length and birth timing. Placental expression of CRH and subsequently prolonged gestational length were found in two independent strains of transgenic mice carrying a 180-kb human bacterial artificial chromosome (BAC) DNA that contained the full length of CRH and extended flanking regions, including THE1B. Restricted deletion of THE1B silenced placental CRH expression and normalized birth timing in these transgenic lines. Furthermore, we revealed an interaction at the 5' insertion site of THE1B with distal-less homeobox 3 (DLX3), a transcription factor expressed in placenta. Together, these findings suggest that retroviral insertion of THE1B into the anthropoid primate genome may have initiated expression of CRH in placental syncytiotrophoblasts via DLX3 and that this placental CRH is sufficient to alter the timing of birth.
Asunto(s)
Hormona Liberadora de Corticotropina/genética , Placenta/metabolismo , Primates/genética , Retroelementos/genética , Animales , Secuencia de Bases , Sistemas CRISPR-Cas/genética , Cromosomas Artificiales Bacterianos/genética , Hormona Liberadora de Corticotropina/metabolismo , Femenino , Redes Reguladoras de Genes , Proteínas de Homeodominio/metabolismo , Humanos , Masculino , Ratones Transgénicos , Mutagénesis Insercional/genética , Parto , Embarazo , Unión Proteica , Eliminación de Secuencia , Especificidad de la Especie , Secuencias Repetidas Terminales/genética , Factores de Transcripción/metabolismo , Trofoblastos/metabolismoRESUMEN
Kruppel-associated box zinc-finger proteins (KRAB-ZFPs) make up the largest family of transcription factors in humans. These proteins emerged in the last common ancestor of coelacanth and tetrapods, and have expanded and diversified in the mammalian lineage. Although their mechanism of transcriptional repression has been well studied for over a decade, the DNA-binding activities and the biological functions of these proteins have been largely unexplored. Recent large-scale ChIP-seq studies and loss-of-function experiments have revealed that KRAB-ZFPs play a major role in the recognition and transcriptional silencing of transposable elements (TEs), consistent with an 'arms race model' of KRAB-ZFP evolution against invading TEs. However, this model is insufficient to explain the evolution of many KRAB-ZFPs that appear to domesticate TEs for novel host functions. We highlight some of the mammalian regulatory innovations driven by specific KRAB-ZFPs, including genomic imprinting, meiotic recombination hotspot choice, and placental growth.
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Elementos Transponibles de ADN , Evolución Molecular , Mamíferos/genética , Proteínas Represoras/fisiología , Animales , Humanos , Dedos de ZincRESUMEN
Transcriptional enhancers control cell-type-specific gene expression. Primed enhancers are marked by histone H3 lysine 4 (H3K4) mono/di-methylation (H3K4me1/2). Active enhancers are further marked by H3K27 acetylation (H3K27ac). Mixed-lineage leukemia 4 (MLL4/KMT2D) is a major enhancer H3K4me1/2 methyltransferase with functional redundancy with MLL3 (KMT2C). However, its role in cell fate maintenance and transition is poorly understood. Here, we show in mouse embryonic stem cells (ESCs) that MLL4 associates with, but is surprisingly dispensable for the maintenance of, active enhancers of cell-identity genes. As a result, MLL4 is dispensable for cell-identity gene expression and self-renewal in ESCs. In contrast, MLL4 is required for enhancer-binding of H3K27 acetyltransferase p300, enhancer activation, and induction of cell-identity genes during ESC differentiation. MLL4 protein, rather than MLL4-mediated H3K4 methylation, controls p300 recruitment to enhancers. We also show that, in somatic cells, MLL4 is dispensable for maintaining cell identity but essential for reprogramming into induced pluripotent stem cells. These results indicate that, although enhancer priming by MLL4 is dispensable for cell-identity maintenance, it controls cell fate transition by orchestrating p300-mediated enhancer activation.
Asunto(s)
Elementos de Facilitación Genéticos , Regulación de la Expresión Génica , N-Metiltransferasa de Histona-Lisina/metabolismo , Animales , Biomarcadores , Diferenciación Celular/genética , Línea Celular , Autorrenovación de las Células/genética , Reprogramación Celular , Proteína p300 Asociada a E1A/metabolismo , Células Madre Embrionarias/citología , Células Madre Embrionarias/metabolismo , Fibroblastos/metabolismo , Técnicas de Inactivación de Genes , N-Metiltransferasa de Histona-Lisina/genética , Histonas/metabolismo , Células Madre Pluripotentes Inducidas/citología , Células Madre Pluripotentes Inducidas/metabolismo , Ratones , Modelos Biológicos , Regiones Promotoras Genéticas , Unión ProteicaRESUMEN
Endogenous retroviruses (ERVs) constitute a substantial portion of mammalian genomes, and their retrotransposition activity helped to drive genetic variation, yet their expression is tightly regulated to prevent unchecked amplification. We generated a series of mouse mutants and embryonic stem (ES) cell lines carrying "deletable" and "rescuable" alleles of the lysine-specific demethylase LSD1/KDM1A. In the absence of KDM1A, the murine endogenous retrovirus MuERV-L/MERVL becomes overexpressed and embryonic development arrests at gastrulation. A number of cellular genes normally restricted to the zygotic genome activation (ZGA) period also become up-regulated in Kdm1a mutants. Strikingly, many of these cellular genes are flanked by MERVL sequences or have cryptic LTRs as promoters that are targets of KDM1A repression. Using genome-wide epigenetic profiling of Kdm1a mutant ES cells, we demonstrate that this subset of ZGA genes and MERVL elements displays increased methylation of histone H3K4, increased acetylation of H3K27, and decreased methylation of H3K9. As a consequence, Kdm1a mutant ES cells exhibit an unusual propensity to generate extraembryonic tissues. Our findings suggest that ancient retroviral insertions were used to co-opt regulatory sequences targeted by KDM1A for epigenetic silencing of cell fate genes during early mammalian embryonic development.
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Células Madre Embrionarias/metabolismo , Células Madre Embrionarias/virología , Regulación del Desarrollo de la Expresión Génica , Oxidorreductasas N-Desmetilantes/metabolismo , Animales , Línea Celular , Células Cultivadas , Histona Desacetilasas/metabolismo , Histona Demetilasas , Histonas/metabolismo , Ratones , Ratones Endogámicos C57BL , Ratones Desnudos , Mutación , Proteínas Nucleares/metabolismo , Oxidorreductasas N-Desmetilantes/genética , Regiones Promotoras Genéticas/genética , Proteínas Represoras/metabolismo , Retroviridae , Proteína 28 que Contiene Motivos Tripartito , Activación Viral/genéticaRESUMEN
Embryonic stem (ES) cells are derived from blastocyst-stage embryos and are thought to be functionally equivalent to the inner cell mass, which lacks the ability to produce all extraembryonic tissues. Here we identify a rare transient cell population within mouse ES and induced pluripotent stem (iPS) cell cultures that expresses high levels of transcripts found in two-cell (2C) embryos in which the blastomeres are totipotent. We genetically tagged these 2C-like ES cells and show that they lack the inner cell mass pluripotency proteins Oct4 (also known as Pou5f1), Sox2 and Nanog, and have acquired the ability to contribute to both embryonic and extraembryonic tissues. We show that nearly all ES cells cycle in and out of this privileged state, which is partially controlled by histone-modifying enzymes. Transcriptome sequencing and bioinformatic analyses showed that many 2C transcripts are initiated from long terminal repeats derived from endogenous retroviruses, suggesting this foreign sequence has helped to drive cell-fate regulation in placental mammals.
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Desdiferenciación Celular/genética , Células Madre Embrionarias/citología , Células Madre Embrionarias/metabolismo , Retrovirus Endógenos/genética , Células Madre Pluripotentes/citología , Células Madre Totipotentes/citología , Células Madre Totipotentes/metabolismo , Animales , Desdiferenciación Celular/fisiología , Linaje de la Célula/genética , Quimera/embriología , Cromatina/genética , Cromatina/metabolismo , Embrión de Mamíferos/citología , Embrión de Mamíferos/metabolismo , Embrión de Mamíferos/virología , Células Madre Embrionarias/virología , Epigénesis Genética , Femenino , Regulación del Desarrollo de la Expresión Génica , Genes Reporteros/genética , Histonas/química , Histonas/metabolismo , Células Madre Pluripotentes Inducidas/citología , Células Madre Pluripotentes Inducidas/metabolismo , Lisina/química , Lisina/metabolismo , Metilación , Ratones , Fenotipo , Células Madre Pluripotentes/metabolismo , Células Madre Pluripotentes/virología , Secuencias Repetidas Terminales/genética , Células Madre Totipotentes/virología , Transcriptoma/genéticaRESUMEN
Histone H3 serine 10 phosphorylation is a hallmark of mitotic chromosomes, but its full function remains to be elucidated. We report here that two SR protein splicing factors, SRp20 and ASF/SF2, associate with interphase chromatin, are released from hyperphosphorylated mitotic chromosomes, but reassociate with chromatin late in M-phase. Inhibition of Aurora B kinase diminished histone H3 serine 10 phosphorylation and increased SRp20 and ASF/SF2 retention on mitotic chromosomes. Unexpectedly, we also found that HP1 proteins interact with ASF/SF2 in mitotic cells. Strikingly, siRNA-mediated knockdown of ASF/SF2 caused retention of HP1 proteins on mitotic chromatin. Finally, ASF/SF2-depleted cells released from a mitotic block displayed delayed G0/G1 entry, suggesting a functional consequence of these interactions. These findings underscore the evolving role of histone H3 phosphorylation and demonstrate a direct, functional, and histone-modification-regulated association of SRp20 and ASF/SF2 with chromatin.
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Cromatina/metabolismo , Histonas/metabolismo , Mitosis , Proteínas Nucleares/metabolismo , Proteínas de Unión al ARN/metabolismo , Serina/metabolismo , Animales , Sitios de Unión , Células Cultivadas , Pollos , Células HeLa , Humanos , Proteínas Nucleares/genética , Nucleosomas/metabolismo , Fosforilación , Proteínas de Unión al ARN/genética , Factores de Empalme Serina-ArgininaRESUMEN
The mammalian egg employs a wide spectrum of epigenome modification machinery to reprogram the sperm nucleus shortly after fertilization. This event is required for transcriptional activation of the paternal/zygotic genome and progression through cleavage divisions. Reprogramming of paternal nuclei requires replacement of sperm protamines with canonical and non-canonical histones, covalent modification of histone tails, and chemical modification of DNA (notably oxidative demethylation of methylated cytosines). In this essay we highlight the role maternal histone variants play during developmental reprogramming following fertilization. We discuss how reduced maternal histone variant incorporation in somatic nuclear transfer experiments may explain the reduced viability of resulting embryos and how knowledge of repressive and activating maternal factors may be used to improve somatic cell reprogramming.