Ontogeny of estrogen receptor-beta expression in rat testis

The recently discovered estrogen receptor-beta (ER beta) is expressed in ro dent and human testes. To obtain insight in the physiological role of ER be ta we have investigated the cell type-specific expression pattern of ER bet a messenger RNA (mRNA) and protein in the testis of rats of various ages by in situ hybridization and immunohistochemistry. In fetal testes of rats 16 days postcoitum and testes of 4-day-old animals, fetal germ cells (gonocyt es) reveal the ER beta mRNA in their cytoplasm and the ER beta protein in t heir nucleus. In testes of 11- and 15-day-old rats, ER beta mRNA and protei n were detected in Sertoli cells and type A spermatogonia. No signal was fo und in other types of germ cells. In the adult testes, expression of ER bet a mRNA as well as ER beta protein was found in pachytene spermatocytes from epithelial stages VII-XIV and in round spermatids from stages I-VIII. Low ER beta expression was observed in all type A spermatogonia, including undi fferentiated A spermatogonia, whereas no expression was found in In and typ e B spermatogonia and early spermatocytes. At all ages, Sertoli cells showe d a weak hybridization signal as well as weak immunoreactivity for ER beta. In adult testes, no ER beta mRNA or protein was detected in the interstiti al tissue, indicating that Leydig cells and peritubular myoid cells do not express ER beta. The expression of ER beta in fetal and late male germ cell s as well as in Sertoli cells suggests that estrogens directly affect germ cells during testicular development and spermatogenesis.