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.