Fig. 4. Testes from control and transgene-positive Ercc1-deficient mice. (A) 3-week wild type, immunostained for Dazl, containing a normal complement of germ cells including pachytene spermatocytes (P) and round spermatids (R). (B) 3-week transgene-positive Ercc1 null, immunostained for Dazl; note that germ cells are present up to and including pachytene spermatocytes (P), but many tubules are SCO (Sertoli cell only, ^*). Although germ cell numbers are reduced compared with wild type (A) they are substantially increased compared to age-matched null animals (Fig. 3F). (C) 6-week wild type, Haematoxylin and Eosin stained; full spermatogenesis is present with germ cells at different stages of development arranged in characteristic associations (stages), mature spermatozoa (s) are seen in the centre of the tubule at stage VIII. (D) 7-week transgene-positive Ercc1 null, Haematoxylin and Eosin stained; note that the germ cell complement is variable with some SCO tubules (^*), whilst in others, although significant germ cell loss has occurred (arrows point to gaps within the epithelium), germ cells including spermatocytes (arrowheads) and elongate spermatids () are present. (E) 10-week wild-type, plastic section; note very occasional small lipid droplets close to the basement membrane (arrows). (F) 10-week transgene-positive Ercc1 null, plastic section; note reduced diameter of the seminiferous tubules due to reduced germ cell numbers (double-headed arrow) compared with age-matched wild type (E), and accumulation of numerous lipid droplets within the Sertoli cells (arrows). Positive lipid staining was noted in interstitial Leydig cells in both wild-type and Ercc1 null testes (L).