EXPRESSION OF PP2A-B REGULATORY SUBUNIT BETA ISOTYPE IN RAT TESTIS

We isolated a rat cDNA encoding part of the beta-isotype of the B regulatory subunit (BRbeta) of protein phosphatase 2A (PP2A), The isolated cDNA encoded the region corresponding to amino acids positions 8(R) to 177(N) of human BRbeta. The identities of the nucleotide and amino acid sequences of the rat and human BRbetas were 95.7% and 100%, respectively. The BRbeta mRNA was specifically expressed in rat brain and testis, the lengths of mRNAs in these two organs being different. In the testis, the BRbeta mRNA was first detected 40 days after birth, increasing gradually thereafter, and was expressed specifically in elongated spermatids, while mRNA of the alpha-isotype (BRalpha) was expressed equally in all spermatogenic cells. After meiosis, round spermatids change morphologically to elongated spermatids. BRbeta may regulate the activity of the PP2A catalytic subunit in spermatids, and be involved in spermatogenic maturation, especially spermatid elongation.