Mammalian follicle-stimulating hormone and insulin-like growth factor I (IGF-I) up-regulate IGF-I gene expression in organ culture of newt testis

We previously showed that porcine follicle-stimulating hormone (pFSH) and h uman recombinant insulin-like growth factor (rhIGF-1) promote the different iation of secondary spermatogonia into primary spermatocytes in organ cultu res of newt testes, respectively. To elucidate the molecular action of FSH and IGF-1, we cloned cDNAs for newt IGF-l and IGF-l receptor (IGF-IR), and examined their mRNA expression in organ culture during newt spermatogenesis . Northern blot and reverse transcription-polymerase chain reaction (RT-PCR ) analyses revealed that IGF-l mRNA was highly expressed in somatic cells ( mostly Sertoli cells) at the secondary spermatogonial stage but barely in g erm cells, and that IGF-IR mRNA was expressed in both germ and somatic cell s at all stages examined. The addition of pFSH to newt testis markedly incr eased IGF-1 mRNA expression. Also, rhIGF-1 increased IGF-1 mRNA expression, whereas IGF-IR mRNA expression declined slightly. These results suggest th at the ability of FSH to promote the differentiation of secondary spermatog onia is at least partly mediated by somatic cell-derived IGF-1, and that IG F-1 mRNA expression in somatic cells is auto-upregulated.