FIG. 17.

Increased numbers of apoptotic germ cells are present in the seminiferous tubules of sir2α null mice. Testis cross sections from wild-type (a) and sir2α null (b) mice were analyzed by the terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick-end labeling (TUNEL) assay to determine the frequency of apoptotic cells. Following exposure to 3 Gy of X-irradiation, the number of TUNEL-positive cells was increased (b and d) in both wild-type and sir2α null mice. The graph at the bottom shows the percentage of seminiferous tubule cross sections with one to three (grey portion of each bar) and more than three (black portion of bar) TUNEL-positive cells. Significantly more apoptotic cells were present in the sir2α null testes than in the wild-type testes (P < 0.05 by Student's unpaired t test).