Cohesin release-factor Wapl modulates axis and chromatin structure to promote conjunction and separation of meiotic chromosomes.

Analysis of meiotic prophase in Sordaria macrospora shows that the cohesin-release factor Wapl is a multi-stage modulator of whole-chromosomal dynamics. Absence of Wapl affects chromosome lengths, but without direct effects on basic recombination events or synaptonemal complex (SC) formation and removal, implying that the fundamental axis structure remains intact. Instead, Wapl is (1) required for regular juxtaposition of homolog/partner axes in space, raising the possibility that cohesin might directly mediate this process; (2) important for telomere dynamics during the bouquet stage and for chromosome-entanglement resolution; and (3) required for correct homolog segregation. Wapl also mediates axis and chromatin disorganization during the transit from SC removal to diplotene (the "diffuse stage") but, nonetheless, allows chromosome reformation into normal diplotene/metaphase states, begging the question of why the diffuse stage exists at all. Notably, Wapl modulates not only the axis state but also, separately, the chromatin state, pointing to direct and/or indirect role(s) for cohesin in that aspect.