Meiotic gene transcription programs are mediated by A-MYB and BRDT-dependent RNA polymerase II pause release during mammalian prophase I

Abstract

During meiotic prophase I, germ cells must balance transcriptional activation with meiotic recombination and chromosome synapsis, biological processes requiring extensive changes to chromatin state and structure. Here we explored the interplay between chromatin accessibility and transcription across a detailed time-course of murine male meiosis by measuring genome-wide patterns of chromatin accessibility, nascent transcription, and processed mRNA. To understand the relationship between these parameters of gene regulation and recombination, we integrated these data with maps of double-strand break formation. Maps of nascent transcription show that Pol II is loaded on chromatin and maintained in a paused state early during prophase I. In later stages of prophase I, paused Pol II is released in a coordinated transcriptional burst resulting in ~3-fold increase in transcription. Release from pause is mediated by the transcription factor A-MYB and the testis-specific bromodomain protein, BRDT. The burst of transcriptional activity is both temporally and spatially segregated from key steps of meiotic recombination: double strand breaks show evidence of chromatin accessibility earlier during prophase I and at distinct loci from those undergoing transcriptional activation, despite shared chromatin marks. Our findings reveal the mechanism underlying chromatin specialization in either transcription or recombination in meiotic cells.

ARID1A governs the silencing of sex-linked transcription during male meiosis in the mouse

“…Along with altered chromatin composition and structure, pachytene spermatocytes lacking ARID1A also displayed an abnormal association of pSer2-RNAPII (elongating form) with the sex body. Normally, total transcriptional output peaks towards the end of meiotic prophase-I, even with MSCI coinciding (Alexander et al, 2022; Ernst et al, 2019; Monesi, 1964). The dynamic switching from the paused (pSer5-RNAPII) to the elongating (pSer2-RNAPII) state of RNAPII drives this burst of transcription on autosomes (Alexander et al, 2022).…”

“…Normally, total transcriptional output peaks towards the end of meiotic prophase-I, even with MSCI coinciding (Alexander et al, 2022; Ernst et al, 2019; Monesi, 1964). The dynamic switching from the paused (pSer5-RNAPII) to the elongating (pSer2-RNAPII) state of RNAPII drives this burst of transcription on autosomes (Alexander et al, 2022). The association of pSer2-RNAPII with the sex chromosomes without ARID1A renders them more autosome-like, underlying the defect in sex-linked gene repression.…”

“…We performed IF to monitor the localization of the actively transcribing (elongating) form of RNAPII marked by Serine2 phosphorylation (pSer2) on its carboxy-terminal domain (Noe Gonzalez et al, 2021). We monitored elongating RNAPII (pSer2) because its pausing regulates meiotic transcription (Alexander et al, 2022). By co-staining for RNAPII (pSer2) and SYCP3, we could stage pachynema and identify the sex chromosomes.…”

ARID1A governs the silencing of sex-linked transcription during male meiosis in the mouse

“…We performed IF to monitor the localization of the actively transcribing (elongating) form of RNAPII marked by Serine2 phosphorylation (pSer2) on its carboxy-terminal domain (Noe Gonzalez et al, 2021 ). We monitored elongating RNAPII (pSer2) because its pausing regulates meiotic transcription (Alexander et al, 2022 ). By co-staining for RNAPII (pSer2) and SYCP3, we could stage pachynema and identify the sex chromosomes.…”

H2A.Z deposition at meiotic prophase I underlies homologous recombination and pachytene genome activation during male meiosis

“…This process, referred to as pachytene genome activation (PGA), is responsible for the expression of numerous genes and plays an essential role in controlling meiotic and post-meiotic events. Previous studies have emphasized the significance of the transcription factors (TFs) A-MYB, BRDT, and TCFL5 in activating transcription during pachytene (Alexander et al, 2023;Bolcun-Filas et al, 2011;Cecchini et al, 2023;Gaucher et al, 2012;Li et al, 2013;Maezawa et al, 2020;Manterola et al, 2018;Ozata et al, 2020;Yu et al, 2021). Additionally, extensive chromatin remodeling takes place in spermatocytes during meiotic prophase I, involving histone variant exchange, histone modifications, and high-order genome rearrangement (Kota and Feil, 2010;Wang et al, 2017;Zheng and Xie, 2019).…”