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 regu latory subunit (BRbeta) of protein phosphatase 2A (PP2A), The isolated cDNA encoded the region corresponding to amino acids positions 8(R) t o 177(N) of human BRbeta. The identities of the nucleotide and amino a cid sequences of the rat and human BRbetas were 95.7% and 100%, respec tively. The BRbeta mRNA was specifically expressed in rat brain and te stis, the lengths of mRNAs in these two organs being different. In the testis, the BRbeta mRNA was first detected 40 days after birth, incre asing gradually thereafter, and was expressed specifically in elongate d spermatids, while mRNA of the alpha-isotype (BRalpha) was expressed equally in all spermatogenic cells. After meiosis, round spermatids ch ange 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.