Sue Marty M, Singh Narendra P, Stebbins Kenneth E, Ann Linscombe V, Passage Julie, Bhaskar Gollapudi B
Toxicology and Environmental Research and Consulting, The Dow Chemical Company, Midland, MI, USA.
Toxicol Pathol. 2010 Feb;38(2):244-57. doi: 10.1177/0192623309357947. Epub 2010 Feb 2.
If p53 is essential to eliminate damaged spermatogenic cells, then mutagen exposure in the absence of p53 would increase sperm containing damaged DNA. p53 knockout (-/-, NULL) and wild-type (+/+, WT) mice (five/group) were exposed to ethylnitrosourea (ENU) or cyclophosphamide (CP). In phase I, mice were exposed by gavage to 0 or 60 mg/kg/day ENU or CP for four days and examined on test day (TD) 4, and in phase II, mice were exposed to 0, 6, 20, or 60 mg/kg/day ENU or CP for four days and evaluated on TD 36 when exposed spermatocytes matured. In phase I, mutagens were not directly cytotoxic to mature sperm. In phase II, WT mice were more sensitive to decreases in reproductive organ weights, whereas both genotypes had decreased sperm counts. Testicular histology revealed similar CP responses, but genotype-specific ENU responses (WT mice had depletion of elongating spermatids; NULL mice had late-stage spermatocyte/early stage spermatid loss). Ethylnitrosourea increased DNA strand breaks in WT mice. Thus, mice responded similarly to CP, suggesting a primarily p53-independent response, whereas the ENU response differed by zygosity, suggesting a role for p53. As DNA damage increased at higher ENU doses, compensatory repair pathways may operate in NULL mice.
如果p53对于清除受损的生精细胞至关重要，那么在缺乏p53的情况下暴露于诱变剂会增加含有受损DNA的精子数量。将p53基因敲除（-/-，无）和野生型（+/+，WT）小鼠（每组五只）暴露于乙基亚硝基脲（ENU）或环磷酰胺（CP）。在第一阶段，小鼠通过灌胃每天给予0或60 mg/kg的ENU或CP，持续四天，并在试验第4天进行检查；在第二阶段，小鼠每天给予0、6、20或60 mg/kg的ENU或CP，持续四天，并在暴露的精母细胞成熟的试验第36天进行评估。在第一阶段，诱变剂对成熟精子没有直接细胞毒性。在第二阶段，野生型小鼠对生殖器官重量的降低更敏感，而两种基因型的精子数量均减少。睾丸组织学显示对CP的反应相似，但对ENU的反应具有基因型特异性（野生型小鼠伸长型精子细胞减少；基因敲除小鼠晚期精母细胞/早期精子细胞丢失）。乙基亚硝基脲增加了野生型小鼠的DNA链断裂。因此，小鼠对CP的反应相似，表明主要是不依赖p53的反应，而对ENU的反应因纯合性而异，表明p53发挥了作用。随着ENU剂量增加DNA损伤加剧，基因敲除小鼠中可能会启动补偿性修复途径。
