Differential expression of c-kit in mouse undifferentiated and differentiating type A spermatogonia.

The proto-oncogene c-kit is encoded at the white-spotting locus and in the mouse mutations at this locus affect the precursor cells of melanocytes, hematopoietic cells, and germ cells. c-kit is expressed in type A spermatogonia, but whether or not c-kit is present both in undifferentiated and differentiating type A spermatogonia or only in the latter cell type is still a matter of debate. Using the vitamin A-deficient mouse model, we studied messenger RNA (mRNA) and protein expression in undifferentiated and differentiating type A spermatogonia. Furthermore, we quantified the immuno-positive type A spermatogonia in the epithelial stages VI, VII, IX/X, and XII in normal mice to correlate c-kit expression in type A spermatogonia with the differentiation of these cells. Our results show that in the VAD situation undifferentiated type A spermatogonia express little c-kit mRNA. The A spermatogonia with a larger nucleus expressed c-Kit protein, whereas the A spermatogonia with a smaller one did not. After induction of differentiation of these cells into type A1 spermatogonia, c-kit mRNA was enhanced. The percentage of A spermatogonia expressing c-Kit protein did not change during this process, suggesting that A spermatogonia, which are committed to differentiate express c-kit. Under normal circumstances in epithelial stage VI 16%+/-2% (mean +/- SD), in VII 45%+/-15%, in IX/X 78%+/-14% and in XII 90%+/-1.9% of the type A spermatogonia were c-kit positive, suggesting that Aaligned spermatogonia gradually change from c-Kit negative to c-Kit positive cells before their differentiation into A1 spermatogonia. It is concluded that c-kit can be used as a marker for differentiation of undifferentiated into differentiating type A spermatogonia.