Rec8p, a Meiotic Recombination and Sister Chromatid Cohesion Phosphoprotein of the Rad21p Family Conserved from Fission Yeast to Humans

Abstract

Our work and that of others defined mitosis-specific (Rad21 subfamily) and meiosis-specific (Rec8 subfamily) proteins involved in sister chromatid cohesion in several eukaryotes, including humans. Mutation of the fission yeast Schizosaccharomyces pombe rec8 gene was previously shown to confer a number of meiotic phenotypes, including strong reduction of recombination frequencies in the central region of chromosome III, absence of linear element polymerization, reduced pairing of homologous chromosomes, reduced sister chromatid cohesion, aberrant chromosome segregation, defects in spore formation, and reduced spore viability. Here we extend the description of recombination 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 Rec8p localizes to approximately 100 foci per prophase nucleus. Rec8p was present in an unphosphorylated form early in meiotic prophase but was phosphorylated prior to meiosis I, as demonstrated by analysis of the mei4mutant blocked 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 expression indicate evolutionarily conserved functions of Rec8p in meiosis. Possible roles of Rec8p in the integration of different meiotic events are discussed.

ACKNOWLEDGMENTS

The first two authors contributed equally to this work.

We thank the following persons for communication of unpublished results: Y. Lin, D. Evans, and G. Smith; W.-D. Heyer and V. Bashkirov; Y. Hiraoka; M. D. Krawchuk and W. P. Wahls; Y. Watanabe and P. Nurse; K. Nasmyth and F. Klein; and W. Warren. We thank H. Scherthan for technical advice, S. Verschoor for technical assistance, J. Hoogerbrugge and A. Grootegoed for fractionated mouse testis cells, and F. Fabre for supplying basic budding yeast strains. M.J.M. thanks colleagues in the Bootsma/Hoeijmakers laboratory for general advice and discussion.

R.K. is a Fellow of the Royal Netherlands Academy of Arts and Sciences. This work was supported by the Swiss National Science Foundation, a grant of the Human Frontier Science Program, the Royal Australasian College of Radiologists, the Netherlands Organization for Scientific Research (NWO; 901-01-097), and International Human Frontier Science Program postdoctoral fellowship LT-506/94 to M.J.M.