GONOCYTES IN TESTES OF NEONATAL RATS EXPRESS THE C-KIT GENE

Information gathered from mutant mouse models and from studies on norm al puberal and adult animals points to the product of the c-kit gene, a tyrosine kinase surface receptor, and the kit-ligand (KL) as importa nt for gametogenesis in males. In fetuses, KL serves as a survival fac tor for primordial germ cells, at least in vitro, and in adults activi ty of the c-kit gene has been indirectly related to survival and subse quent develop ment of differentiating spermatogonia. However, because of the structural complexity of the seminiferous epithelium iri adults , c-kit mRNA has not yet been definitively localized to one or more ty pes of spermatogenic cells. In addition, no information is currently a vailable regarding the possible involvement of the c-kit protein and i ts ligand in mediating germ cell development and/or Sertoli-germ cell interactions immediately after birth when events critical for later on set of spermatogenesis are ongoing. Thus, the aims of the current stud y were (1) to determine whether the c-kit gene is expressed in testes of neonatal and adult rats and, if so, by what specific cell types, an d (2) to determine if those cells expressing the gene also produce the c-kit receptor protein. For this, we isolated total RNA from testes o f pups aged days 1-5 and from adult rat testes, and probed for the pre sence of c-kit mRNA with Northern analysis. We identified the cells co ntaining the c-kit message by carrying out in situ hybridization with digoxigenin-labeled probes, thus allowing the colorimetric signal to b e assigned beyond doubt to individual cells in sections of testes. We also utilized Western analysis and immunolocalization to confirm the p resence of the c-kit receptor protein in testes at these ages and to i dentify those cells types producing it. Our findings indicate that (1) neonatal gonocytes express the c-kit gene and produce the receptor pr otein on postnatal days 1 through 5, spanning the time when they resum e dividing and migrating, and (2) spermatogonia and, to a lesser exten t, spermatocytes and spermatids of adults express the gene but c-kit p rotein is present in detectable amounts only in spermatogonia and poss ibly a few early primary spermatocytes. (C) 1996 Wiley-Liss, Inc.