Germ cell specific expression of c-kit in the human fetal gonad

The proto-oncogene receptor, c-kit, and its ligand have been demonstrated to be essential to the processes of germ cell migration, proliferation and survival in the rodent. The aim of the present study was to investigate the expression of c-kit mRNA and protein in human fetal ovary and testis across the gestational period 13-21 weeks. In the ovary, this crucial period of development spans the transition from oogonial replication by mitosis to primordial follicle formation. In the testis, germ cells (gonocytes) are mitotically active. Expression of c-kit mRNA was demonstrated by reverse transcription-polymerase chain reaction (RT-PCR) in both ovary and testis at all gestational ages examined. Testicular germ cell specific expression of c-kit mRNA was confirmed by RT-PCR using specific cell types recovered by laser capture microscopy. The expression of c-kit protein by both male and female germ cells was demonstrated by immunohistochemistry at all gestational ages examined, and was confirmed by immunoblotting. In both, c-kit was localized to the cell membrane except in oocytes within primordial follicles where it was localized to the cytoplasm. These data demonstrate that the expression of c-kit mRNA and protein is germ cell specific in human fetal gonads and are consistent with an important role for the c-kit/kit ligand signalling system in germ cell proliferation and survival in the developing human gonad.