Effects of FGF9 on embryonic Sertoli cell proliferation and testicular cord formation in the mouse.

Proliferation and cord formation by embryonic Sertoli cells are pivotal events involved in testis morphogenesis. A number of growth factors have been implicated in mediating these events. However, the exact level of involvement and importance of each as yet remains elusive. We have adopted an in vitro approach to assess developing mouse Sertoli cells, whereby they are cultured in the presence or absence of fibroblast growth factor (FGF9) and/or extracellular matrix (ECM) gel, since previous studies have shown that ECM gel aids Sertoli cell differentiation. The present findings corroborate this effect, but in addition demonstrate that in the presence of FGF9 (10 ng/ml), cells undergo greater proliferation than those cultured on gel alone. They also display a differentiated epithelial phenotype, with appositional contact of cell membranes in cord-like aggregations. In addition we have shown that cultured Sertoli cells generally express a smaller truncated, nuclear form of the FGFr3, although in the presence of FGF9 and absence of gel, the larger, cytoplasmic form of the receptor is also expressed. Immunolocalisation of FGFr3 in Sertoli cells of whole testes revealed a temporal expression pattern profile, with high levels being abundant in the embryonic testicular cords and at puberty, but an absence in adult Sertoli cells. Our findings suggest that FGF9 plays an important role in proliferation and organisation of embryonic Sertoli cells during testis morphogenesis.