Changes in Leydig cell gene expression during development in the mouse. Biol Reprod 66: 966–975

Developmental changes in the expression of 18 Leydig cell-specific mRNA species were measured by real-time polymerase chain reaction to partially characterize the developmental phe-notype of the cells in the mouse and to identify markers of adult Leydig cell differentiation. Testicular interstitial webs were iso-lated from mice between birth and adulthood. Five develop-mental patterns of gene expression were observed. Group 1 con-tained mRNA species encoding P450 side chain cleavage (P450scc), P450c17, relaxin-like factor (RLF), glutathione S-trans-ferase 5-5 (GST5-5), StAR protein, LH receptor, and epoxide hy-drolase (EH); group 2 contained 3b-hydroxysteroid dehydroge-nase (3b-HSD) VI, 17b-hydroxysteroid dehydrogenase (17b-HSD) III, vascular cell adhesion molecule 1, estrogen sulfotrans-ferase, and prostaglandin D (PGD)-synthetase; group 3 contained patched and thrombospondin 2 (TSP2); group 4 con-tained 5a-reductase 1 and 3a-hydroxysteroid dehydrogenase; group 5 contained sulfonylurea receptor 2 and 3b-HSD I. Group 1 contained genes that were expressed in fetal and adult Leydig cells and which increased in expression around puberty toward a maximum in the adult. Group 2 contained genes expressed only in the adult Leydig cell population. Group 3 contained genes with predominant fetal/neonatal expression in the inter-stitial tissue. Group 4 contained genes with a peak of expression around puberty, whereas genes in group 5 show little develop-mental change in expression. Highest mRNA levels in descend-ing order were RLF, P450c17, EH, 17b-HSD III, PGD-synthetase, GST5-5, and P450scc. Results identify five genes expressed in the mouse adult Leydig cell population, but not in the fetal popu-lation, and one gene (TSP2) that may be expressed only in the fetal Leydig cell population. The developmental pattern of gene expression suggests that three distinct phases of adult Leydig cell differentiation occur. developmental biology, gene regulation, Leydig cells, testis, tes-tosteron