SYCP2 and SYCP3 are required for cohesin core integrity at diplotene but not for centromere cohesion at the first meiotic division.

Much of the organization of the meiotic prophase-I chromosome axis is attributed to two groups of proteins: the axial element proteins, SYCP2 and SYCP3; and the cohesin-complex proteins. Although the cohesin-complex proteins ensure that sister chromatids remain paired during meiosis, the role of SYCP2 and SYCP3 is not clear. Interestingly, it has been shown that SYCP3 and SYCP2 associate with the centromere regions of male, but not female, metaphase-I chromosomes, suggesting a sex-specific function for the two proteins. We have analysed the spatial distribution of cohesin-complex proteins associated with meiotic chromosomes in germ cells derived from Sycp3-deficient female and male mice. We show that, in the absence of SYCP3, the cohesin cores associated with the female meiotic chromosomes disassemble prematurely at the diplotene stage of meiosis. We also show that SYCP3 and SYCP2 are not required for centromere cohesion at the metaphase-I stage in male germ cells. We conclude that SYCP3 has a temporally restricted role in maintaining, but not establishing, cohesin-core organization during prophase I. This finding supports a model in which the removal of bulk cohesin from paired sister chromatids at late prophase in both meiotic and mitotic cells ensures proper chromosome compaction and segregation.