Dynamic changes in ovarian c-kit and Steel expression during the estrous reproductive cycle.

W and Steel mutant mice exhibit similar developmental defects in melanogenesis, haematopoiesis, and gametogenesis. Consistent with the cell autonomous and microenvironmental nature of W and Sl mutations, respectively, W encodes the c-kit receptor tyrosine kinase while Steel encodes the Kit ligand. Both c-kit and Steel are expressed in various cells in which no corresponding mutant phenotype has yet been demonstrated. In the adult ovary, certain stromal-derived cells (theca and interstitial), as well as oocytes, express c-kit, while granulosa cells express Steel. We show here that the cessation of oocyte growth, at the transition of the follicle to the antral stage, is associated with the cessation of Steel expression in the cumulus granulosa cells in the vicinity of the oocyte. These observations suggest a role for the Kit signaling pathway in oocyte growth or in meiotic arrest. In addition, the cyclic secretion of luteinizing hormone immediately and dramatically results in elevated Steel expression in mural granulosa cells and decreased levels of c-kit transcripts in stromal-derived cells. This influence of the estrous reproductive cycle on c-kit/Steel expression suggests that the Kit signaling pathway, in addition to its previously described role in primordial germ cell development, is involved in follicular development in the adult female.