Fig. 3. Testes from control and Ercc1-null mice immunostained for the germ cell-specific marker Dazl. (A) 3-day wild type, (B) 3-day Ercc1 null, (C) 12-day wild type, (D) 12-day Ercc1 null, (E) 22-day wild type, (F) 22-day Ercc1 null. The number of germ cells in the Ercc1 nulls was reduced compared with wild-type littermates at all ages examined. The number of germ cells in individual tubules in the nulls was highly variable even within the same testis. Tubules devoid of germ cells (^*) and germ cells with abnormal morphology (arrows) in the nulls were seen at all ages.