Ontogeny of stem cell factor receptor (c-kit) messenger ribonucleic acid in the ovine corpus luteum.

Stem cell factor (SCF) is a pleiotropic growth factor that is expressed by the ovine corpus luteum throughout its life span by both small and large steroidogenic cells. Determination of the action of SCF, however, requires localization of its receptor, c-kit; therefore, the objectives of the present study were to identify and localize c-kit within corpora lutea. Two cDNAs encoding different portions of the c-kit molecule were amplified by the polymerase chain reaction. The first was a 558-base pair (bp) cDNA encoding portions of the transmembrane and tyrosine kinase domains; the second was a 632-bp cDNA encoding most of the ligand-binding domain. Expression of c-kit was quantified by RNase protection assay of total cellular RNA collected on Days 3, 7, 10, 13, and 16 (n = 4, 4, 5, 4, and 4 per group, respectively) of the estrous cycle (Day 0 = estrus). The level of c-kit mRNA was low early in the luteal phase, reached (p < 0.05) maximum levels on Day 13, and then decreased (p < 0.01) on Day 16. On Day 3 (n = 4), c-kit was expressed in a cell-specific manner throughout the corpus luteum; identity of the specific cell types expressing c-kit could not be determined at this stage. On Day 14 (n = 4), c-kit did not appear to be expressed within large luteal cells but was prominently expressed in cells that surrounded large luteal cells and that possessed the morphological characteristics of small luteal cells and endothelial cells. Given the temporal regulation of c-kit expression within the corpus luteum, these data suggest that luteal SCF may act locally.