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Characterization of the distribution and dynamics of chromatin states in the C. elegans germ line reveals substantial H3K4me3 remodeling during oogenesis

ABSTRACT: Chromatin organization in the C. elegans germ line is tightly regulated and critical for germ cell differentiation. While certain germline epigenetic regulatory mechanisms have been identified, how they influence chromatin structure and ultimately gene expression remains unclear, in part because most genomic studies have focused on data collected from whole worms. We therefore analyzed publicly available histone modification and chromatin accessibility data from isolated undifferentiated germ nuclei to define chromatin states. We then correlated these states with overall transcript abundance, spatio-temporal expression patterns, and the function of small RNA pathways. Because the essential role of the germ line is to transmit genetic information to the next generation and establish gene expression in the early embryo, we compared epigenetic and transcriptomic profiles from undifferentiated germ cells, oocytes, and embryos to define the epigenetic changes during this developmental transition. The active histone modification H3K4me3 exhibits particularly dynamic remodeling as germ cells differentiate into oocytes, with implications for establishing transcriptional activation of essential genes during early embryogenesis. Our results highlight the dynamism of the chromatin landscape in germ cells, and provide a resource for future investigation into epigenetic regulatory mechanisms.

ORGANISM(S): Caenorhabditis elegans

PROVIDER: GSE236076 | GEO | 2023/07/03

REPOSITORIES: GEO

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Project description:In mammals, totipotent pre-implantation embryos are formed by fusion of highly differentiated oocytes and spermatozoa. Acquisition of totipotency concurs with remodeling of chromatin states of parental genomes (M-bM-^@M-^\epigenetic reprogrammingM-bM-^@M-^]), changes in maternally contributed transcriptome and proteome, and zygotic genome activation. Genomes of mature germ cells are more proficient in supporting embryonic development than those of somatic cells. It is currently unknown whether transgenerational inheritance of chromatin states present in mature gametes underlies the efficacy of early embryonic development after natural conception. Here, we show that Ring1 and Rnf2, two core components of the Polycomb Repressive Complex 1 (PRC1), serve redundant gene regulatory functions during oogenesis that are required to support embryonic development beyond the two-cell stage. Numerous developmental regulatory genes that are established Polycomb targets in various somatic cell types are de-repressed in Ring1/Rnf2 double mutant (dm) fully grown germinal vesicle (GV) oocytes. Translation of tested aberrant maternal transcripts is, however, delayed until after fertilization. Exchange of maternal pro-nuclei between control and Ring1/Rnf2 maternally dm early zygotes demonstrates an essential role for Ring1 and Rnf2 during oogenesis in defining cytoplasmic and nuclear maternal contributions that are both essential for proper initiation of embryonic development. A large number of genes up-regulated in Ring1/Rnf2 dm GV oocytes harbor PRC2-mediated histone H3 lysine 27 trimethylation (H3K27me3) in spermatozoa and in embryonic stem cells (ESCs), and are repressed during normal oogenesis and early embryogenesis. These data strongly support the model that Polycomb acts in the female and male germline to silence differentiation inducing genes and to program chromatin states, thereby sustaining developmental potential across generations. Expression profiling of fully grown mouse GV oocytes was performed with the following genotypes: Ring1+/+Rnf2F/F (control), Ring1-/-Rnf2F/F (Ring1 mutant), Ring1+/+Rnf2F/FZp3-cre (Rnf2 mutant) and Ring1-/-Rnf2F/FZp3-cre (Ring1/Rnf2 double mutant). 12 samples were analyzed: 3 biological replicates of each of the 4 genotypes (Ring1+/+Rnf2F/F (control), Ring1-/-Rnf2F/F (Ring1 mutant), Ring1+/+Rnf2F/FZp3-cre (Rnf2 mutant) and Ring1-/-Rnf2F/FZp3-cre (Ring1/Rnf2 double mutant)). Each sample contains 50 GV oocytes.

Project description:In mammals, totipotent pre-implantation embryos are formed by fusion of highly differentiated oocytes and spermatozoa. Acquisition of totipotency concurs with remodeling of chromatin states of parental genomes (“epigenetic reprogramming”), changes in maternally contributed transcriptome and proteome, and zygotic genome activation. Genomes of mature germ cells are more proficient in supporting embryonic development than those of somatic cells. It is currently unknown whether transgenerational inheritance of chromatin states present in mature gametes underlies the efficacy of early embryonic development after natural conception. Here, we show that Ring1 and Rnf2, two core components of the Polycomb Repressive Complex 1 (PRC1), serve redundant gene regulatory functions during oogenesis that are required to support embryonic development beyond the two-cell stage. Numerous developmental regulatory genes that are established Polycomb targets in various somatic cell types are de-repressed in Ring1/Rnf2 double mutant (dm) fully grown germinal vesicle (GV) oocytes. Translation of tested aberrant maternal transcripts is, however, delayed until after fertilization. Exchange of maternal pro-nuclei between control and Ring1/Rnf2 maternally dm early zygotes demonstrates an essential role for Ring1 and Rnf2 during oogenesis in defining cytoplasmic and nuclear maternal contributions that are both essential for proper initiation of embryonic development. A large number of genes up-regulated in Ring1/Rnf2 dm GV oocytes harbor PRC2-mediated histone H3 lysine 27 trimethylation (H3K27me3) in spermatozoa and in embryonic stem cells (ESCs), and are repressed during normal oogenesis and early embryogenesis. These data strongly support the model that Polycomb acts in the female and male germline to silence differentiation inducing genes and to program chromatin states, thereby sustaining developmental potential across generations. Expression profiling of fully grown mouse GV oocytes was performed with the following genotypes: Ring1+/+Rnf2F/F (control), Ring1-/-Rnf2F/F (Ring1 mutant), Ring1+/+Rnf2F/FZp3-cre (Rnf2 mutant) and Ring1-/-Rnf2F/FZp3-cre (Ring1/Rnf2 double mutant).

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Characterization of the distribution and dynamics of chromatin states in the C. elegans germ line reveals substantial H3K4me3 remodeling during oogenesis

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