Rec8p, a meiotic recombination and sister chromatid cohesion phosphoprotein of the Rad21p family conserved from fission yeast to humans

Our work and that of others defined mitosis-specific (Rad21 subfamily) and meiosis-specific (Rec8 subfamily) proteins involved in sister chromatid coh esion in several eukaryotes, including humans. Mutation of the fission yeas t Schizosaccharomyces pombe rec8 gene was previously shown to confer a numb er of meiotic phenotypes, including strong reduction of recombination frequ encies in the central region of chromosome III, absence of linear element p olymerization, reduced pairing of homologous chromosomes, reduced sister ch romatid cohesion, aberrant chromosome segregation, defects in spore formati on, and reduced spore viability. Here we extend the description of recombin ation reduction to the central regions of chromosomes I and II. We show at the protein level that expression of rec8 is meiosis specific and that Rec8 p localizes to approximately 100 foci per prophase nucleus. Rec8p was prese nt in an unphosphorylated form early in meiotic prophase but was phosphoryl ated prior to meiosis I, as demonstrated by analysis of the mei4 mutant blo cked before meiosis I. Evidence for the persistence of Rec8p beyond meiosis I was obtained by analysis of the mutant mes1 blocked before meiosis II. A human gene, which we designate hrec8, showed significant primary sequence similarity to rec8 and was mapped to chromosome 14. High mRNA expression of mouse and human rec8 genes was found only in germ line cells, specifically in testes and, interestingly, in spermatids. hrec8 was also expressed at a low level in the thymus. Sequence similarity and testis-specific expressio n indicate evolutionarily conserved functions of Rec8p in meiosis. Possible roles of Rec8p in the integration of different meiotic events are discusse d.