CXXC1 is redundant for normal DNA double-strand break formation and meiotic recombination in mouse

Abstract

2In most mammals, including mice and humans, meiotic recombination is determined by the 1 3 meiosis specific histone methytransferase PRDM9, which binds to specific DNA sequences and 1 4trimethylates histone 3 at lysine-4 and lysine-36 at the adjacent nucleosomes. These actions 1 5 ensure successful DNA double strand break initiation and repair that occur on the proteinaceous 1 6 structure forming the chromosome axis. The process of hotspot association with the axis after 1 7 their activation by PRDM9 is poorly understood. Previously, we and others have identified 1 8 CXXC1, an ortholog of S. cerevisiae Spp1 in mammals, as a PRDM9 interactor. In yeast, Spp1 1 9 is a histone methyl reader that links H3K4me3 sites with the recombination machinery, 2 0 promoting DSB formation. Here we investigated whether CXXC1 has a similar function in 2 1 mouse meiosis. We found that CXXC1 is co-expressed and interacts with PRDM9 in mouse 2 2 spermatocytes. To investigate the meiotic function of CXXC1, we created a Cxxc1 conditional 2 3 knockout mouse to deplete CXXC1 before the onset of meiosis. Surprisingly, knockout mice 2 4were fertile, and the loss of CXXC1 in spermatocytes had no effect on hotspot trimethylation 2 5 activity, double-strand break formation or repair. Our results demonstrate that CXXC1 is not an 2 6 essential link between recombination hotspot sites and DSB machinery and that the hotspot 2 7 recognition pathway in mouse is independent of CXXC1. 2 8 2 9 3 0

EWSR1 affects PRDM9-dependent histone 3 methylation and provides a link between recombination hotspots and the chromosome axis protein REC8

“…Although we show that EWSR1 participates in hotspot association with the chromosome axis, our data suggest that it cannot be the only protein to do so, because a significant share of PRDM9-dependent hotspots are forming DSBs in CKO spermatocytes. Another proposed candidate, CXXC1 (Imai et al, 2017;Parvanov et al, 2017), does not seem to be important in the PRDM9-dependent hotspot recognition pathway (Tian et al, 2018), which raises the question of what other proteins, if any, may be involved in this process. In somatic cells, EWSR1 is reported to be involved in RNA-related functions such as transcription regulation and RNA binding (Fisher, 2014;Schwartz et al, 2015).…”

EWSR1 affects PRDM9-dependent histone 3 methylation and provides a link between recombination hotspots and the chromosome axis

“…Although we show that EWSR1 participates in hotspot association with the chromosome axis, our data suggest that it cannot be the only protein to do so, because a significant share of PRDM9-dependent hotspots are forming DSBs in CKO spermatocytes. Another proposed candidate, CXXC1 [27, 49], does not seem to be important in the PRDM9-dependent hotspot recognition pathway [50], which raises the question of what other proteins, if any, may be involved in this process. In somatic cells, EWSR1 is reported to be involved in RNA-related functions such as transcription regulation and RNA binding [51, 52].…”