Immunocytochemical observation of the 90 KD heat shock protein (HSP90): high expression in primordial and pre-meiotic germ cells of male and female rat gonads.

We used immunocytochemistry to detect the 90 KD major heat shock protein (HSP90), a potential regulator of gene expression, during male and female rat gonad development. In the Day 13.0 post-coital (dpc) fetal gonad, strong immunoreactivity to anti-HSP90 antibody was shown in the cytoplasm of primordial germ cells (PGCs). Other somatic cells in the gonad showed only faint reactivity. During testicular development, strong immunostaining was observed in the cytoplasm of embryonic germ cells and in spermatogonia and spermatocytes of the pre-pubertal testis. In adult testis reactivity of spermatogonia and pachytene spermatocytes was strong but reactivity of post-meiotic spermatogenic cells, i.e., secondary spermatocytes and spermatids, was extremely reduced. During ovarian development, immunostaining was also observed in the oogonia and the oocytes of pre-pubertal ovary. However, the staining of oocytes was reduced with the development of primordial follicles during the first week after birth. This study revealed that HSP90 is highly expressed in PGCs and continues to be expressed in both male and female pre-meiotic germ cells. The HSP90 accumulation may be essential for both male and female mammalian pre-meiotic germ cells.