233. A role for activin/inhibin in mouse gonocyte relocation and proliferation

Abstract

Gonocytes in the testis resume proliferation after birth and relocate to contact the basement membrane of the seminiferous cords where they become spermatogonia. A previous in vitro study indicated that activin can increase gonocyte numbers on day 3 postpartum (dpp) rat testis, while the activin antagonist, follistatin, together with FSH, increased the number of spermatogonia (Meehan et al. 2000). The aim of this study was to understand how FSH, activin and inhibin, a potent activin antagonist, interact to influence gonocyte proliferation and relocation in the newborn mouse testis using in vivo and in vitro approaches. Two mouse models were analysed, the inhibin α knock out (inh a −/−) mouse and the InhbaBK mouse. The Inh a −/− mouse lacks inhibin, and thus activin acts unopposed by its most potent antagonist (Matzuk et al. 1992). The InhbaBK mouse has the Inhbb allele inserted into the Inhba locus, thus directing the expression of the less bioactive activin βB, in the spatiotemporal pattern of activin βA (Brown et al. 2000). In addition, an in vitro model was developed in which 1dpp wild type testis fragments were cultured in hanging drops for 24 h with the addition of combinations of activin, inhibin and FSH. Gonocyte proliferation in inh a −/− was assessed using proliferating cell nuclear antigen (PCNA). A significant increase in germ cell proliferation and relocation to the basement membrane was measured in 0dpp inh a −/−, while no difference was observed at 4dpp. The opposite was observed in InhbaBK mice, with reduced gonocyte migration in mutant animals at 0dpp. In vitro, inhibin seemed to inhibit proliferation and reduce the percentage of relocated gonocytes while FSH showed a tendency for the opposite effect on gonocyte migration. These findings show that inhibin levels affect germ cell development during early postnatal development in mouse testis influencing both cell maturation and proliferation. (1) Meehan T, Schlatt S, O'Bryan MK, de Kretser DM, Loveland KL. Regulation of germ cell and Sertoli cell development by activin, follistatin, and FSH. Dev Biol. 2000 Apr 15;220(2):225–37. (2) Matzuk MM, Finegold MJ, Su JG, Hsueh AJ, Bradley A. Alpha-inhibin is a tumour-suppressor gene with gonadal specificity in mice. Nature. 1992 Nov 26;360(6402):313–9. (3) Brown CW, Houston-Hawkins DE, Woodruff TK, Matzuk MM. Insertion of Inhbb into the Inhba locus rescues the Inhba null phenotype and reveals new activin functions. Nat Genet. 2000 Aug;25(4):453–7.