FIG. 7.

PCNA-positive cells in seminiferous tubules of mice of different genotypes. Sections of testes from mice of the indicated genotypes (top) taken at day 15, day 19, and 3 months pp (indicated at the left) were immunostained with an antibody against PCNA. A deep purple precipitate indicates cellular proliferation that, in adult males, is eventually restricted to a single or double layer of premeiotic germ cells on the periphery of the seminiferous tubules (I through L). At day 19 pp, more widespread proliferation is observed in the tubules of single Ink4-null (F and G) and Ink4cd double-null males (H) as compared to the patterns in wild-type (WT) mice (E).