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, he matopoietic cells, and germ cells. c-kit is expressed in type A spermatogon ia, but whether or not c-kit is present both in undifferentiated and differ entiating type A spermatogonia or only in the latter cell type is still a m atter of debate. Using the vitamin A-deficient mouse model, we studied mess enger RNA (mRNA) and protein expression in undifferentiated and differentia ting type A spermatogonia. Furthermore, me quantified the immuno-positive t ype A spermatogonia in the epithelial stages VI, VII, IX/X, and XII in norm al mice to correlate c-kit expression in type A spermatogonia with the diff erentiation of these cells. Our results show that in the VAD situation undi fferentiated type A spermatogonia express little c-kit mRNA. The A spermato gonia with a larger nucleus expressed c-kit protein, whereas the A spermato gonia with a smaller one did not. After induction of differentiation of the se cells into type A(1) spermatogonia, c-Kit mRNA was enhanced. The percent age of A spermatogonia expressing c-Kit protein did not change during this process, suggesting that A spermatogonia, which are committed to differenti ate 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 A (aligned) spermatogonia gradually change from c-Kit negative to c-Kit posit ive cells before their differentiation into A(1) spermatogonia. It is concl uded that c-kit can be used as a marker for differentiation of undifferenti ated into differentiating type A spermatogonia.