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Anatomy of the insulin-like growth factor system in the human testis
1Developmental Endocrinology Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892.
Objective:
To study the cellular patterns of gene expression for insulin-like growth factors I and II (IGF-I and IGF-II), their receptors and specific high-affinity binding proteins (IGFBPs) in the human testis.
Design:
In situ hybridization histochemistry was used to localize messenger ribonucleic acids (mRNAs) for IGF-I and IGF-II, the IGF-I and IGF-II receptors and IGFBP-1 to 6 in fresh-frozen testis sections from healthy young men who died of trauma.
Results:
Insulin-like growth factor I mRNA was not detected. Insulin-like growth factors II mRNA was abundant in testicular blood vessels and peritubular connective tissue. Both IGF-I and IGF-II receptor mRNAs were most abundant in the germinal epithelium. Insulin-like growth factor binding protein 1 mRNA was not detected. Binding protein-2 mRNA was expressed in both Leydig and Sertoli cells. Binding protein-3 mRNA was detected only in the endothelium of testicular blood vessels. Binding protein-4 mRNA was also localized in endothelium but, in addition, was present in Leydig cells and interstitial connective tissue. Binding protein-5 mRNA was abundant in connective tissue and was detected at low levels in Leydig cells. Binding protein-6 mRNA was present in some of the peritubular cells and in some cells of the interstitial compartment.
Conclusion:
Our results suggest that IGFs may play significant roles in testicular function and germ cell development.