title: Genome organization and epigenetic marks in mouse germinal vesicle oocytes.
abstract: During the final step of oogenesis, the oocyte nucleus is subject to large-scale modifications that correlate with transcriptional silencing. While oocytes with dense chromatin around the nucleolus are silent (SN, surrounded nucleolus), oocytes with uncondensed chromatin (NSN, non-surrounded nucleolus) are transcriptionally active. It is believed that epigenetic mechanisms that participate in gene expression regulation could play a role in this event. In this context, we examined the behaviour of heterochromatin and related histone modifications during the NSN to SN transition by immunostaining. Using fluorescent in situ hybridization on three dimensional-preserved nuclei (3D-FISH), we also studied the distribution of centromeric, pericentromeric and ribosomal (rDNA) sequences in relation to the nucleolus (also called the nucleolus-like body, NLB).  We observed that in NSN-type oocytes, pericentromeric heterochromatin is aggregated within chromocenters. In SN-type oocytes, pericentromeric heterochromatin and centromeres form a discontinuous ring around the NLB. rDNA sequences, which initially present a pearl necklace structure, gather together in seven highly condensed foci at the NLB periphery. H3K9me3 and H4K20me3 heterochromatin marks clearly label chromocenters, whereas H3K4me3 and H4K5ac are totally excluded from heterochromatin regions, even in the very compact SN-nuclei. Remarkably, H3K27me3 displays an intermediate behavior. It appears that GV oocyte nuclei exhibit a specific epigenetic landscape. Histone modifications, related to both active and repressive chromatin structures, seem to follow the large-scale chromatin movements that occur during the NSN to SN transition. We also demonstrate that, while heterochromatin regions re-localize around the NLB, rDNA sequences adopt a highly compact structure in SN-type oocytes.
authors: UMR1198 Biologie du Développement et Reproduction, Institut National de la Recherche Agronomique, Jouy-en-Josas, France. amelie.bonnet-garnier@jouy.inra.fr
authors: Amelie
authors: A
authors: Bonnet-Garnier
authors: Prisca
authors: P
authors: Feuerstein
authors: Martine
authors: M
authors: Chebrout
authors: Renaud
authors: R
authors: Fleurot
authors: Habib-Ullah
authors: HU
authors: Jan
authors: Pascale
authors: P
authors: Debey
authors: Nathalie
authors: N
authors: Beaujean
mesh_terms: D000818:Animals; D002466:Cell Nucleolus / Q000235:genetics; D002467:Cell Nucleus / Q000235:genetics*; D002503:Centromere / Q000235:genetics; D002843:Chromatin / Q000235:genetics / Q000378:metabolism; D004275:DNA, Ribosomal / Q000235:genetics; D044127:Epigenesis, Genetic; D057890:Epigenomics; D005260:Female; D016678:Genome / Q000235:genetics*; D006570:Heterochromatin / Q000235:genetics / Q000378:metabolism; D006657:Histones / Q000378:metabolism; D017404:In Situ Hybridization, Fluorescence; D008745:Methylation; D051379:Mice; D008810:Mice, Inbred C57BL; D008808:Mice, Inbred CBA; D008856:Microscopy, Fluorescence; D009865:Oocytes / Q000166:cytology / Q000378:metabolism*; D009866:Oogenesis / Q000235:genetics
chemical_list: D002843:Chromatin; D004275:DNA, Ribosomal; D006570:Heterochromatin; D006657:Histones