Identification of receptor tyrosine kinases in the rat testis

Evidence of receptor/ligand interactions that regulate testis cell function was sought in order to broaden the current understanding of the molecular basis of testis cell function. Using reverse transcription and the polymerase chain reaction, we have obtained novel evidence for the expression of three mRNAs encoding receptor tyrosine kinases in the adult rat testis: the platelet-derived growth factor type A receptor (PDGF-RA), the basic fibroblast growth factor receptor (flg), and fetal liver kinase 1 (Flk-1). A 6.8 kb transcript encoding the PDGF-RA was observed in RNA prepared from testes of rats aged day 5 through adult, with a decline in relative abundance with increasing age after day 17. Analysis of mRNA from isolated cell preparations (day 21 Sertoli cells, adult Leydig cells, round spermatids, and primary spermatocytes) and testes depleted of specific cell types [ethane dimethane sulfonate (EDS)-treated and cryptorchid] indicated that the Leydig cell was the predominant source of this mRNA in the adult testis. The addition of PDGF-BB to cultures of highly purified adult rat Leydig cell preparations resulted in a 40% increase in LH-stimulated testosterone production, confirming a role for this growth factor in regulation of Leydig cell function. These data indicate that the Leydig cell is a principal site of action of PDGF in the testis.