CHARACTERIZATION OF THE HEAT-SHOCK PROTEIN P70 IN RAT SPERMATOGENIC CELLS

A number of hsp70-like proteins are associated with developing male ge rm cells. One of these molecules, P70, is not sensitive to heat stress and is germ cell-specific, and its expression is developmentally regu lated. We have characterized the association of the rat P70(rP70) with differentiating germ cells in the testis and with posttesticular sper m. An antibody originally raised against human sperm proacrosin (desig nated C3; Siegel et al., 1987: J Reprod Immunol 11:307-319) was found to immunostain rP70 by immunoblot analysis and was used in subsequent studies of the rP70 molecule. The C3 antibody reacted with P70 isoform s in rat, human, mouse, guinea pig, boar, and rooster testicular homog enates. In the developing rat testis, abundant rP70 protein levels wer e first detected on postnatal day 22, with upregulation to adult level s occurring after postnatal day 28. Purified populations of adult rat pachytene spermatocytes, round spermatids, and elongating spermatids, isolated by unit gravity velocity sedimentation, all expressed rP70. P osttesticular sperm exhibited a loss of the rP70 molecule; caput epidi dymal sperm were weakly immunoreactive for rP70, but no immunoreactivi ty was observed in either cauda epididymal sperm or epididymal fluid. In contrast to human ejaculated sperm, rat ejaculated sperm did not ex press rP70. The loss of P70 from rat posttesticular sperm may reflect species-specific differences in P70 functions, which are thought to in clude a role in the structural modifications that occur during germ ce ll differentiation. (C) 1995 Wiley-Liss, Inc.