Fig. 1. Appearance of Ngn3-positive spermatogonia and Kit-positive spermatogonia during the first postnatal week. (A) RT-PCR of whole testis mRNA at P1 to P7; amplification for Ngn3, Kit, Ret, and Oct4. No bands are observed in control reactions without reverse transcriptase; no template, amplification product without cDNA. ß-actin was also assayed as a control. (B) ISH of sections from testes at P1 to P7, probed for the same gene set described in A. Green and blue arrowheads indicate the Ngn3 and Kit signals in spermatogonia, respectively; red arrowheads indicate Kit expression in the interstitial cells. Scale bar: 100 µm.