Nakayama Y, Yamamoto T, Abé S I
Department of Materials and Life Science, Graduate School of Science and Technology, Kumamoto University, Japan.
Int J Dev Biol. 1999 Jul;43(4):343-7.
Recombinant human insulin-like growth factors (rhIGF-I and rhIGF-II) and human insulin promoted the differentiation of spermatogonia into primary spermatocytes in newt testes fragments cultured in a chemically defined medium. The biological potency for promoting differentiation was dose-dependent for all the ligands with the highest potency displayed by IGF-I, followed by IGF-II, and the least by insulin. The difference in potency was larger between IGF-II and insulin than that between IGF-I and IGF-II. This order of biological potency was in good accordance with the order of affinity in binding specificity of [125I]IGF-I to the testicular membrane fractions: IGF-II and insulin competed the binding of [125I]IGF-I only at concentrations 20-fold and 100-fold higher, respectively, than IGF-I. Specific binding was observed in both somatic cells (mostly Sertoli cells) and germ cells (spermatogonia and primary spermatocytes), though the binding to somatic cells was about 2.7 times higher than that to germ cells. These results indicate that (1) specific binding sites for IGF-I are present in the newt testes, (2) IGF-II and insulin also bind to these receptors but to a lesser degree, and (3) IGF-II and insulin as well as IGF-I promote spermatogonial differentiation into primary spermatocytes by binding to the IGF-I receptor.
重组人胰岛素样生长因子（rhIGF-I和rhIGF-II）以及人胰岛素促进了蝾螈睾丸组织块在化学成分明确的培养基中培养时精原细胞向初级精母细胞的分化。对于所有配体而言，促进分化的生物学活性呈剂量依赖性，其中IGF-I的活性最高，其次是IGF-II，胰岛素的活性最低。IGF-II与胰岛素之间活性的差异大于IGF-I与IGF-II之间的差异。这种生物学活性顺序与[125I]IGF-I与睾丸膜组分结合特异性的亲和力顺序高度一致：IGF-II和胰岛素分别仅在比IGF-I高20倍和100倍的浓度下才能竞争[125I]IGF-I的结合。在体细胞（主要是支持细胞）和生殖细胞（精原细胞和初级精母细胞）中均观察到特异性结合，尽管与体细胞的结合比与生殖细胞的结合高约2.7倍。这些结果表明：（1）蝾螈睾丸中存在IGF-I的特异性结合位点；（2）IGF-II和胰岛素也能与这些受体结合，但程度较低；（3）IGF-II、胰岛素以及IGF-I通过与IGF-I受体结合促进精原细胞分化为初级精母细胞。
