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Poised chromatin and bivalent domains facilitate the mitosis-to-meiosis transition in the male germline

ABSTRACT: The male germline transcriptome changes dramatically during the mitosis-to-meiosis transition to activate late spermatogenesis genes and to transiently suppress genes commonly expressed in somatic lineages and spermatogenesis progenitor cells, termed somatic/progenitor genes. These changes reflect epigenetic regulation. Induction of late spermatogenesis genes during spermatogenesis is facilitated by poised chromatin established in the stem cell phases of spermatogonia, whereas silencing of somatic/progenitor genes during meiosis and postmeiosis is associated with formation of bivalent domains which also allows the recovery of the somatic/progenitor program after fertilization. Importantly, during spermatogenesis mechanisms of epigenetic regulation on sex chromosomes are different from autosomes: X-linked somatic/progenitor genes are suppressed by meiotic sex chromosome inactivation without deposition of H3K27me3. Our results suggest that bivalent H3K27me3 and H3K4me2/3 domains are not limited to developmental promoters (which maintain bivalent domains that are silent throughout the reproductive cycle), but also underlie reversible silencing of somatic/progenitor genes during the mitosis-to-meiosis transition in late spermatogenesis.

ORGANISM(S): Mus musculus

PROVIDER: GSE69946 | GEO | 2015/06/18

SECONDARY ACCESSION(S): PRJNA287221

REPOSITORIES: GEO

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Project description:In the mammalian testis, the pool of spermatogonia is amplified by mitosis before these progenitor germ cells undergo meiosis to generate the haploid cells that give rise to sperm. Extensive changes in the transcriptome accompany the onset of the pachytene stage of meiosis, including the transcriptional activation of meiotic genes, the pachytene piRNA pathway, as well as mRNAs required later during spermiogenesis. How transcription is regulated to ensure the precise timing of this major reprogramming of gene expression remains largely uncharacterized. Here, we report that the testis-specific transcription factor TCFL5 is initially activated by the transcription factor A-MYB during meiosis. Subsequently, A-MYB and TCFL5 mutually reinforce their own transcription establishing a central regulatory circuit that regulates meiosis and spermiogenesis, as well as mediates pachytene piRNA production. TCFL5 drives the transcription of 476 genes required for meiosis including genes encoding pachytene piRNA biogenesis proteins, and 796 genes required for spermiogenesis. Tcfl5−/− mutant mice are sterile and spermatogenesis arrests at the mid- or late-pachytene stage of meiosis. Intriguingly, Tcfl5 haploinsufficiency leads to reduced male fertility suggesting germ cells are sensitive to Tcfl5 dosage to develop. Compromised TCFL5 expression underlies the reduced fertility phenotype directly or indirectly through regulating other transcription factors in Tcfl5+/− mutant mice. TCFL5 drives the transcription of evolutionarily younger pachytene piRNAs, while A-MYB regulates older pachytene piRNAs. Older and younger piRNAs mutually initiate their own processing providing evidence how these selfish genetic elements hijack meiotic transcriptional network to amplify themselves. We also demonstrate that TCFL5-mediated regulation of male meiosis and piRNA production is conserved in macaque. Our data establish a direct role of TCFL5 in ensuring the simultaneous activation of genes required for meiosis and spermiogenesis in mammals.

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Poised chromatin and bivalent domains facilitate the mitosis-to-meiosis transition in the male germline

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