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Single-cell staging of meiotic entry identifies a sequential order in meiotic sex chromosome activation

ABSTRACT: The switch from mitosis to meiosis is a major transition that takes place during germ cell development. The precise sequence and the different gene expression programs activated during this process are only partly known. Here, we applied single-cell mRNA sequencing to interrogate the transcriptional changes that occur during the early steps of male germ cell differentiation. We isolated single cells from testes using a Dazl-GFP reporter mouse, which allowed us to focus on germ cells undergoing the mitotic to meiotic transition. We identified 4 distinct meiotic stages with unique transcriptome profiles and reconstructed the timeline of the meiotic entry in silico, from spermatogonia up to the pachytene stage, identifying transcriptional changes with an unprecedented resolution. This allowed us to characterize 3 major transitions in the meiotic prophase 1 of the male germline: meiotic entry, the meiotic sex chromosome inactivation (MSCI), and concomitant pachytene transcriptional activation. Meiotic entry is initiated following the downregulation of a tightly connected set of pluripotency factors and accompanied by a global transcriptional silencing. In contrast, during subsequent sex chromosome inactivation at the zygotene stage, gene silencing proceeds in a defined order, related to gene function.

ORGANISM(S): Mus musculus

PROVIDER: GSE114788 | GEO | 2021/05/22

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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Single-cell staging of meiotic entry identifies a sequential order in meiotic sex chromosome activation

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