Essential role of paternal chromatin in the regulation of transcriptional activity during mouse preimplantation development.
ABSTRACT Several lines of evidence indicate that the formation of a transcriptionally repressive state during the two-cell stage in the preimplantation mouse embryo is superimposed on the activation of the embryonic genome. However, it is difficult to determine the profile of newly synthesized (nascent) RNA during this phase because large amounts of maternal RNA accumulate in maturing oocytes to support early development. Using 5-bromouridine-5'-triphosphate labeling of RNA, we have verified that nascent RNA synthesis was repressed between the two-cell and four-cell transition in normally fertilized but not in parthenogenetic embryos. Moreover, this repression was contributed by sperm (male) chromatin, which we confirmed by studying androgenetic embryos. The source of factors responsible for repressing nascent RNA production was investigated using different stages of sperm development. Fertilization with immature round spermatids resulted in a lower level of transcriptional activity than with ICSI at the two-cell stage, and this was consistent with further repression at the four-cell stage in the ICSI group. Finally, study on DNA replication and chromatin remodeling was performed using labeled histones H3 and H4 to differentiate between male and female pronuclei. The combination of male and female chromatin appeared to decrease nascent RNA production in the fertilized embryo. This study indicates that paternal chromatin is important in the regulation of transcriptional activity during mouse preimplantation development and that this capacity is acquired during spermiogenesis.
- SourceAvailable from: Sung-Joon Park[Show abstract] [Hide abstract]
ABSTRACT: Fertilization precisely choreographs parental genomes by using gamete-derived cellular factors and activating genome regulatory programs. However, the mechanism remains elusive owing to the technical difficulties of preparing large numbers of high-quality preimplantation cells. Here, we collected >14 × 10(4) high-quality mouse metaphase II oocytes and used these to establish detailed transcriptional profiles for four early embryo stages and parthenogenetic development. By combining these profiles with other public resources, we found evidence that gene silencing appeared to be mediated in part by noncoding RNAs and that this was a prerequisite for post-fertilization development. Notably, we identified 817 genes that were differentially expressed in embryos after fertilization compared with parthenotes. The regulation of these genes was distinctly different from those expressed in parthenotes, suggesting functional specialization of particular transcription factors prior to first cell cleavage. We identified five transcription factors that were potentially necessary for developmental progression: Foxd1, Nkx2-5, Sox18, Myod1, and Runx1. Our very large-scale whole-transcriptome profile of early mouse embryos yielded a novel and valuable resource for studies in developmental biology and stem cell research. The database is available at http://dbtmee.hgc.jp.Genes & Development 12/2013; 27(24):2736-48. · 12.44 Impact Factor
- Reproduction Fertility and Development 07/2012; · 2.58 Impact Factor
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ABSTRACT: In mammalian spermatozoa, most but not all of the genome is densely packaged by protamines. Here we reveal the molecular logic underlying the retention of nucleosomes in mouse spermatozoa, which contain only 1% residual histones. We observe high enrichment throughout the genome of nucleosomes at CpG-rich sequences that lack DNA methylation. Residual nucleosomes are largely composed of the histone H3.3 variant and are trimethylated at Lys4 of histone H3 (H3K4me3). Canonical H3.1 and H3.2 histones are also enriched at CpG-rich promoters marked by Polycomb-mediated H3K27me3, a modification predictive of gene repression in preimplantation embryos. Histone variant-specific nucleosome retention in sperm is strongly associated with nucleosome turnover in round spermatids. Our data show evolutionary conservation of the basic principles of nucleosome retention in mouse and human sperm, supporting a model of epigenetic inheritance by nucleosomes between generations.Nature Structural & Molecular Biology 06/2013; · 11.90 Impact Factor