Genetic Evidence That Synaptonemal Complex Axial Elements Govern Recombination Pathway Choice in Mice

Abstract

Chiasmata resulting from interhomolog recombination are critical for proper chromosome segregation at meiotic metaphase I, thus preventing aneuploidy and consequent deleterious effects. Recombination in meiosis is driven by programmed induction of double strand breaks (DSBs), and the repair of these breaks occurs primarily by recombination between homologous chromosomes, not sister chromatids. Almost nothing is known about the basis for recombination partner choice in mammals. We addressed this problem using a genetic approach. Since meiotic recombination is coupled with synaptonemal complex (SC) morphogenesis, we explored the role of axial elements -precursors to the lateral element in the mature SC -in recombination partner choice, DSB repair pathways, and checkpoint control. Female mice lacking the SC axial element protein SYCP3 produce viable, but often aneuploid, oocytes. We describe genetic studies indicating that while DSB-containing Sycp3 2/2 oocytes can be eliminated efficiently, those that survive have completed repair before the execution of an intact DNA damage checkpoint. We find that the requirement for DMC1 and TRIP13, proteins normally essential for recombination repair of meiotic DSBs, is substantially bypassed in Sycp3 and Sycp2 mutants. This bypass requires RAD54, a functionally conserved protein that promotes intersister recombination in yeast meiosis and mammalian mitotic cells. Immunocytological and genetic studies indicated that the bypass in Sycp3 2/2 Dmc1 2/2 oocytes was linked to increased DSB repair. These experiments lead us to hypothesize that axial elements mediate the activities of recombination proteins to favor interhomolog, rather than intersister recombinational repair of genetically programmed DSBs in mice. The elimination of this activity in SYCP3-or SYCP2-deficient oocytes may underlie the aneuploidy in derivative mouse embryos and spontaneous abortions in women.

Differentiation of spermatogonial stem cell-like cells from murine testicular tissue into haploid male germ cells in vitro

“…Although mGSCs have been differentiated into spermatogenic cells when they were co-cultured in vitro with feeder layer cells, treated with RA or transplantated in vivo (Feng et al 2002;Kanatsu-Shinohara et al 2003), few reports have shown that murine SSCs are induced in vitro to form haploid male germ cells using RA. Sycp3 and TH2B, specific markers of haploid male germ cells (Lim et al 2010;Li et al 2011), are expressed by haploid male germ cells, as seen in our result. In addition, the result from cell analysis by indirect immunofluorescence demonstrated that haploid male germ cells largely expressed protamine 1 (Fig.…”

Evolutionary history of the mammalian synaptonemal complex

“…Conversely to the situation in mammals, the htp-3 mutant of C. elegans suggests that an AE component might be critical in early recombination initiation in this organism (Goodyer et al 2008). Yet some previous genetic studies in mice proposed that, even though not necessary for DSB formation, AEs function in recombination pathway choice and direct recombination proteins to favor interhomolog rather than intersister recombination repair of DSBs in meiosis (Kouznetsova et al 2011;Li et al 2011). Definitely, DSB formation is required for further steps of homolog pairing and synapsis in mammals but not in C. elegans and Drosophila where synapsis is DSB-independent (Page and Hawley 2003).…”

Multiple Barriers to Nonhomologous DNA End Joining During Meiosis inDrosophila

“…In addition, for a crossover to generate a chiasma, the crossover must occur between homologs and not between sisters. Thus, there appears to be a barrier (or semipermeable barrier) between the sister chromatids that promotes homolog exchange, possibly involving the activity of chromosome axis proteins (Couteau et al 2004;Webber et al 2004;Niu et al 2005;Kim et al 2010;Li et al 2011). Finally, homologous repair must be promoted while more error-prone mechanisms that could introduce de novo mutations in the germline such as nonhomologous end joining (NHEJ) are inhibited.…”