Analyses of mRNA expression patterns of cohesin subunits Rad21 and Rec8 in mice: germ cell-specific expression of rec8 mRNA in both male and female mice.

A multisubunit protein complex called cohesin is required for the cohesion between sister chromatids in both mitosis and meiosis in yeast. We investigate here the mRNA expression patterns of mouse homologues of the yeast mitotic cohesin rad21 and the meiotic cohesin rec8 in various organs, with special attention to their expression in gonads. Northern blot and reverse transcription-polymerase chain reaction (RT-PCR) analyses revealed that, in contrast to the ubiquitous expression of rad21 mRNA in all of the organs examined, rec8 was expressed only in the gonads. We conducted in situ hybridization analysis to identify the cells that express rad21 and rec8 mRNAs in the gonads. In the testis, rad21 mRNA was expressed in somatic cells and spermatogonia but not in spermatocytes, and conversely, rec8 mRNA was expressed in spermatocytes but not in spermatogonia or somatic cells. Spermatids expressed rad21 and rec8 mRNAs simultaneously. In the ovary, rad21 mRNA was detected in all of the ovarian cells including germ cells and somatic cells, whereas rec8 mRNA was detected only in oocytes. Unlike the widespread expression of rad21 gene, therefore, the gene expression of rec8 is strictly confined to spermatocytes and spermatids in male mouse and oocytes in female mouse. The restricted expression pattern of rec8 mRNA implies its essential role in meiosis in both sexes of mammals, as has been reported in yeast. We also discuss the cooperative functions of Rad21 and Rec8 on the basis of the finding that their mRNAs are coexpressed in oocytes and spermatids.