Seasonal Changes in Immunoreactivity of Inhibin/Activin Subunits in the Epididymis of Wild Ground Squirrels (Citellus dauricus Brandt)
Inhibin/activin subunit (alpha, beta A, and beta B) immunoreactive protein localization patterns and cell type specific inhibin alpha-subunit mRNA expression have been examined in early- to midgestational age human fetal testes. The scarcity of available third trimester human fetal tissue has, however prevented a complete examination throughout the gestational period and the cell specific expression of follistatin and beta A- and beta B-subunit mRNAs are currently unknown at any gestational age. In the present study, this gap is filled and report mRNA expression patterns of inhibin/activin subunits in mid- and late-gestational age (21-33 wk) human fetal testes and testicular duct system. We also report the first examination of follistatin mRNA signals in the human fetal gonad is also resent in both tubular and interstitial cells, and beta B-subunit mRNA is expressed in seminiferous tubules, in mid- and late-gestational age human fetal testes. Inhibin/activin beta A-subunit mRNA was detected in the interstitial cells of remarkably well preserved mid (21 and 22 wk) and late (29 wk) gestational age testes, and is the only activin-system factor mRNA also expressed in tissue of the duct system of the testis (smooth muscle cells of the epididymis). Follistatin mRNA signal was equal to background levels in testicular and duct tissues at all ages examined. These cell specific expression patterns suggest prominent and possibly differential roles for the inhibins and activins, unopposed by gonadal follistatin, in the human fetal male reproductive system.