Analysis of functions of DNA polymerase? with knockout mice.

DNA损伤的修复对于维持基因组的完整性至关重要。在哺乳动物细胞中，DNA聚合酶β (Polβ)与碱基切除修复有关。然而，这种酶在体内的生理意义尚不清楚。我们之前已经证明，pol β缺陷小鼠在出生后立即死于呼吸衰竭，并且小鼠在发育中的神经系统中表现出广泛的凋亡细胞死亡。细胞死亡发生在新生成的有丝分裂后神经元细胞中，而不是在有丝分裂祖细胞中，并且与神经发生的发生和停止密切相关。在这项研究中，我们通过产生具有ATM、scid或p53缺陷的双敲除小鼠，研究了这些蛋白在诱导神经细胞死亡中的潜在作用。这些蛋白与DNA损伤感知、细胞周期中的检查点控制和细胞凋亡有关。与Polβ-/-小鼠相比，Polβ-/- atm -/和Polβ-/-scid小鼠在发育早期表现出胚胎致死性。相反，p53缺失可以完全挽救pol β缺失小鼠的神经元凋亡，这表明在pol β缺失的发育神经系统中发现p53是诱导细胞凋亡所必需的。出乎意料的是，Polβ-/-p53-/-小鼠在出生后死亡，表现出Polβ-/-小鼠的神经系统异常。这些结果表明，Polβ在有丝分裂后细胞向成熟神经元的分化中起着关键作用。另一方面，我们通过与HITEC小鼠杂交，研究了Polβ缺乏对组织突变的影响。我们发现，与野生型小鼠相比，Polβ-null小鼠的胚胎大脑突变频率降低，但在肾脏、肝脏和胸腺中没有发现差异。

Repair of DNA damage is essential for the maintenance of genomic integrity. In mammalian cells, DNA polymerase β (Polβ) has been implicated in base excision repair. However, the physiological significance of the enzyme in the body remains unclear. We have previously shown that Polβ-deficient mice die of a respiratory failure immediately after the birth and that the mice exhibit extensive apoptotic cell death in the developing nervous systems. The cell death occurs in newly generated postmitotic neuronal cells rather than in mitotic progenitor cells and is closely linked to the onset and cessation of neurogenesis. In this study, by generating double knockout mice with mice deficient in ATM, scid, or p53, we examined potential roles of these proteins in the induction of neural cell death. These proteins are implicated in DNA damage sensing, checkpoint control in the cell cycle and apoptosis. Polβ-/ -Atm-/-and Polβ-/-scid mice exhibited embryonic lethal at the early developmental stage compared with Polβ-/-mice. In contrast, p53 deficiency could completely rescue neuronal apoptosis in Polβ-null mice, indication that p53 is required for the induction of apoptosis found in the Polβ-deficient developing nervous system. Unexpectedly, Polβ-/-p53-/- mice died after the birth, showing abnormalities of the nervous system as observed in Polβ-/-mice. These results suggest that Polβ plays a critical role in the differentiation of postmitotic cells into a mature neuron. On the other hand, we examined the effect of Polβ deficiency on mutations in tissues using intercrosses with HITEC mice. We found that embryonic brains of Polβ-null mice show a decreased mutant frequency compared with wild-type mice, although no difference was found in kidney, liver and thymus.