Deletion of the intrinsic pathway of apoptosis in the hematopoietic system protects mice from death after whole-body gamma irradiation (WBI). A. Western blot for BAX and tubulin in spleen, lymph node, and thymus from Tie2Cre; Bak1^−/−; Bax^FL/− mice (FL/−) demonstrates deletion of Bax in the hematopoietic system. Tie2Cre; Bak1^−/−; Bax^FL/+ mice (FL/+) retain Bax and serve as a control. B. Kaplan-Meier survival analysis of Tie2Cre; Bak1^−/−; Bax^FL/+ mice and Tie2Cre; Bak1^−/−; Bax^FL/− litter mates after 12.5 Gy WBI. By log-rank comparison, p = 0.0001.

Deletion of the intrinsic pathway of apoptosis from endothelial cells does not protect mice from subtotal-body gamma irradiation (SBI). A. Western blot for BAX and Vinculin from lung endothelial cells isolated from mice that contained no Cre (−), VillinCre (Villin), or Tie2Cre (Tie2) and the indicated Bax genotype. B. Mesenchymal cell (endothelial cell and lymphocyte) apoptosis is decreased in Tie2Cre; Bak1^−/−; Bax^FL/− mice. TUNEL (brown) and MECA-32 (pink) immunohistochemistry identify apoptotic mesenchymal cells within the villi of Tie2Cre; Bak1^−/−; Bax^FL/+ mice. Scale bar, 100 μm. C. Quantification of mesenchymal cell apoptosis in the villi of the distal small intestine. The mean number of mesenchymal cells undergoing apoptosis in a total of at least 87 villi from 3 mice is shown; *p < 0.01 by two-tailed t test. Error bars indicate SEM. D. Kaplan-Meier survival analysis of Tie2Cre; Bak1^−/−; Bax^FL/+ mice and Tie2Cre; Bak1^−/−; Bax^FL/− litter mates after 16.55 Gy SBI. By log-rank comparison, p =NS.

Deletion of the intrinsic pathway of apoptosis from GI epithelial cells does not protect mice from subtotal-body gamma irradiation (SBI). A. Western blot for BAX and Vinculin from GI epithelial cells isolated from mice without Cre (−), with VillinCre (VL), or Tie2Cre (T2), and the indicated Bax genotype. B. Hematoxylin and eosin stained sections of distal small intestine 4 hours after 16.95 Gy SBI demonstrates suppression of apoptosis within the crypt epithelium in VillinCre; Bak1^−/−; Bax^FL/− mice. A green asterisk labels cells with characteristic apoptotic morphology. Scale bar, 100 μm. C. Quantification of GI epithelial cell apoptosis in the crypts of the distal small intestine. The mean number of apoptotic cells in a total of at least 100 crypts in 3 mice is shown. Error bars indicate SEM. *p < 0.01, by two-tailed t test. Similar results were observed in the proximal small intestine. D. Kaplan-Meier survival analysis of VillinCre; Bak1^−/−; Bax^FL/+ and VillinCre; Bak1^−/−; Bax^FL/− mice after 16.95 Gy SBI. By log-rank comparison, p = NS.

Regulation of the GI syndrome by p53 in epithelial cells is independent of apoptosis. A. Quantification of normal (NL) and aberrant (AB) mitoses in GI crypt epithelial cells of the proximal and distal small intestine from wild-type mice without (−) or 24 hours after (+) 13.4 Gy SBI with ionizing radiation. The mean number of mitoses per crypt in a total of at least 115 crypts from 6 mice is shown. Error bars indicate SEM. *p < 0.04 for aberrant mitoses, two-sided t test and **p < 0.005 for normal mitoses, two-sided t test. B. Kaplan-Meier survival analysis of VillinCre; p53^FL/+ and VillinCre; p53^FL/− mice after 16.15 Gy SBI with gamma irradiation. p = 0.0015 by log-rank test. C. Kaplan-Meier survival analysis of at least 9 mice of each of the indicated genotype after 15 Gy SBI with gamma irradiation. p = 0.0001 between p53^FL/− and p53^FL/+ mice and p = NS between Bax^FL/− and Bax^FL/+ mice by log-rank test. D. Kaplan-Meier survival analysis of “super p53” tg^b mice and C57/BL6 p53^+/+ littermate controls after 13.4 Gy SBI with ionizing radiation. p = 0.02 by log-rank test.