DEVELOPMENTAL EXPRESSION OF HEAT-SHOCK PROTEIN-60 (HSP60) IN THE RAT TESTIS AND OVARY

Heat shock protein 60 (HSP60), a member of the chaperonin family, has an essential role in mediating correct folding of nuclear encoded prot eins imported to mitochondria. We have investigated immunocytochemical expression of HSP60 in developing fetal, newborn, postnatal, and pube rtal testis and ovary, and in the adult ovary of the rat. In the fetal gonads, HSP60 was expressed in the germ cells organized into sex cord s and in the developing Leydig cells of the testis. In the pubertal te stis, Leydig cells were strongly, spermatogonia and premeiotic spermat ocytes moderately labeled, spermatids unlabeled. In the postnatal ovar y, oocytes at all stages of folliculogenesis were positive for HSP60. In the pubertal ovary, glandular theca cells, and in the mature ovary, also the cells of the corpora lutea exhibited intense cytoplasmic lab eling. At the electron microscopic level, immunogold particles were lo calized in the mitochondrial matrix, and in the Western blot analysis the antibody detected one single band of 60 kDa. Anti-HSP60 labeling i n male and female sex steroid producing cells and their progenitors se ems to be coordinated with the functional differentiation of these end ocrine cells of the gonad. In the oocytes, a key element required for proper folding of imported mitochondrial proteins seems to be constitu tively expressed throughout folliculogenesis. However, the data sugges t that in the male germ cells mitochondrial chaperonin HSP60 is either not needed during the haploid phase of spermatogenesis or its level b ecomes extensively reduced and therefore undetectable by the methods u sed in the study.