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RNA-seq transcriptome profiling of 1) C. elegans male germlines vs. oogenic germlines, and 2) male germlines, sperm, and F1 offspring germlines when offspring inherited sperm chromatin lacking H3K27me3.

ABSTRACT: Paternal contributions to epigenetic inheritance are not well understood. We report that in C. elegans sperm, the genome is packaged in nucleosomes and carries a histone-based epigenetic memory of gene expressions during spermatogenesis. In mature sperm, genes with spermatogenesis-specific expression are marked with both active and represseive histone modifications and genes with oogenesis-enriched expression are marked with active histone modifications. We showed that genes with oogenesis-enriched expression are in fact transcribed in spermatogenic germlines. We tested if sperm chromatin marking is necessary for germ cell development in offspring that inherit both sperm and oocyte chromosomes, using male parents that either can or cannot generate H3K27me3. Males homozygous for a mutation in mes-3, which encodes a member of the worm PRC2 complex, were mated with feminized mes-3/+ heterozygous worms to produce offspring that inherited sperm chromosomes lacking H3K27me3. We call these offspring M+P- or MpPm (Maternal chromosomes are + or plus for H3K27me3, Paternal chromosomes are - or minus for H3K27me3). Most of the resulting mes-3 homozygous M+P- offspring developed into sterile adults in this sensitized genetic background. In contrast, genetically identical control offspring that received appropriate H3K27me3-marked sperm chromosomes (M+P+ or MpPp) displayed low sterility. We compared genes mis-regulated in mes-3 male germlines versus control him-8 male germlines, mature sperm from those germlines, and germlines of mes-3 mutant F1 offspring that inherited sperm chromatin lacking H3K27me3 (M+P-) versus inherited sperm chromatin with H3K27me3 (M+P+), based on RNA-seq.

ORGANISM(S): Caenorhabditis elegans

PROVIDER: GSE115708 | GEO | 2018/07/23

REPOSITORIES: GEO

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Project description:RNA-seq transcriptome analysis of C. elegans germlines that inherited only paternal chromosomes (non-Mendelian inheritance, 'red-head worms') and the germlines of their offspring ('offspring of red-head worms') vs. germlines that inherited both maternal and paternal chromosomes (Mendelian inheritance, HBR1280 control). Given that epigenetic marking of sperm chromosomes is faithfully transmitted through embryo cell divisions, and that sperm epigenetic marking is important in offspring, we tested if sperm epigenetic marking alone is sufficient for proper development of the germline in offspring. We utilized a mutant that, during the first embryonic division, delivers the sperm genome to the daughter cell that generates the germline and the oocyte genome to the other daughter cell (Besseling & Bringmann, 2016). This mutant over-expresses GPR-1, a protein involved in regulation of kinetochore pulling forces. GPR-1 over-expression results in excessive pulling forces, causing the paternal and maternal pronuclei to inappropriately move to opposite poles of the 1-cell embryo instead of merging in the center of the embryo. In this mutant background, ~60% of offspring undergo atypical chromosome segregation, generating mosaic embryos whose germlines are derived entirely from sperm chromosomes (Besseling & Bringmann, 2016). To track the parental genomes, differentially tagged histone transgenes were used: a GFP-tagged histone H2B encoded in the sperm genome, and a TdTomato-tagged histone H2B encoded in the oocyte genome. The mosaic embryos whose germline inherited only sperm chromosomes (‘red-head' worms) develop into fertile adults with a normal brood size, similar to control worms, in which the germline inherited both sperm and oocyte chromosomes. RNA-seq analysis demonstrated that the germline transcriptome of ‘red-head’ worms and their offspring show few (<80 genes) and minor changes compared to control worms. These findings demonstrate that epigenetic information provided by sperm can guide proper germ cell development.

Project description:Background: Non-genetic disease inheritance and offspring phenotype is substantially influenced by germline epigenetic programming, including genomic imprinting. Loss of Polycomb Repressive Complex 2 (PRC2) function in oocytes causes non-genetically inherited effects on offspring, including embryonic growth restriction followed by post-natal offspring overgrowth. While PRC2 dependent non-canonical imprinting is likely to contribute, less is known about germline epigenetic programming of non-imprinted genes during oocyte growth. In addition, de novo germline mutations in genes encoding PRC2 lead to overgrowth syndromes in human patients, but the extent to which PRC2 activity is conserved in human oocytes is poorly understood. Results: In this study we identify a discrete period of early oocyte growth during which PRC2 is expressed in mouse growing oocytes. Deletion of Eed during this window led to the de-repression of 343 genes. A high proportion of these were developmental regulators, and the vast majority were not imprinted genes. Many of the de-repressed genes were also marked by the PRC2-dependent epigenetic modification histone 3 lysine 27 trimethylation (H3K27me3) in primary-secondary mouse oocytes, at a time concurrent with PRC2 expression. In addition, we found H3K27me3 was also enriched on many of these genes by the germinal vesicle (GV) stage in human oocytes, strongly indicating that this PRC2 function is conserved in the human germline. However, while the 343 genes were de-repressed in mouse oocytes lacking EED, they were not de-repressed in pre-implantation embryos and lost H3K27me3 during pre-implantation development. This implies that H3K27me3 is a transient feature that represses a wide range of genes in oocytes. Conclusions: Together, these data indicate that EED has spatially and temporally distinct functions in the female germline to repress a wide range of developmentally important genes, and that this activity is conserved in the mouse and human germlines.

Dataset Information

RNA-seq transcriptome profiling of 1) C. elegans male germlines vs. oogenic germlines, and 2) male germlines, sperm, and F1 offspring germlines when offspring inherited sperm chromatin lacking H3K27me3.

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