ABSTRACT
Meiotic sex chromosome inactivation (MSCI) is a critical feature of meiotic prophase I progression in males. While the ATR kinase and its activator TOPBP1 are key drivers of MSCI within the specialized sex body (SB) domain of the nucleus, how they promote silencing remains unclear given their multifaceted meiotic functions that also include DNA repair, chromosome synapsis and SB formation. Here we report a novel mutant mouse harboring mutations in the TOPBP1-BRCT5 domain. Topbp1B5/B5 males are infertile, with impaired MSCI despite displaying grossly normal events of early prophase I, including synapsis and SB formation. Specific ATR-dependent events are disrupted including phosphorylation and localization of the RNA:DNA helicase Senataxin. Topbp1B5/B5 spermatocytes initiate, but cannot maintain ongoing, MSCI. These findings reveal a non-canonical role for the ATR-TOPBP1 signaling axis in MSCI dynamics at advanced stages in pachynema and establish the first mouse mutant that separates ATR signaling and MSCI from SB formation.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
- Inclusion of original references about sex body (line 86). - Improvement of scale bar displayed in Figure 1I and 1J. - Inclusion of a comment (results section) about the subtle increase in X-linked genes expression during spermatogonia stage in Topbp1B5/B5 (lines 317-322). - Discussion points raised by peer-reviewers: 1.The possibility of a subtle disruption in XY silencing initiation in Topbp1B5/B5, which is now better emphasized in the discussion (lines 391-394). 2.A discussion point included in lines 392-400 about not all X and Y genes increasing their expression in pachytene if MSCI is ablated with examples of other MSCI-defective mutants. 3.Inclusion of a discussion point about the differences in the abundancies of MLH1 and MLH3 (lines 491-497) 4.Expanded the discussion about SETX function in lines 470-474. 5.Added a discussion point raised by the reviewer (lines 513-522) about the possibility of the expression of XY-linked genes represent a regulated response to meiotic defects to stop meiosis progression, leading to the cell death observed in Topbp1B5/B5, which makes the Topbp1B5/B5 an unique model for these studies as most of the previous meiosis mutants are unable to reach the stage at which MSCI is properly established. - Statistical analysis of meiotic spreads data (after consulting with a Statistician from Cornell Statistics Unit), and sc-RNA-sequencing data (Figures 6 and 7).
