Elevated DNA double strand breaks and apoptosis in the CNS of scid mutant mice

Abstract

Genetic approaches have provided evidence that DNA endjoining problems serve an essential role in neuronal survival during development of mammalian embryos. In the present study, we tested whether the DNA repair enzyme, DNA dependent protein kinase, plays an important role in the survival of cerebral cortical neurons in mice. DNA-PK is comprised of a DNA-binding subunit called Ku and a catalytic subunit called DNA-PKcs. In mice with the scid mutation, DNAPKcs is truncated near the kinase domain, which causes loss of kinase activity. We compared the spatial and temporal aspects of neuronal cell death in scid versus isogenic wildtype embryos and found a significant increase in dying cells in scid mice, as assessed by nuclear changes, DNA fragmentation and caspase-3 activity. Additional biochemical and immunocytochemical studies indicated that of several DNA repair enzymes investigated, only PARP was increased in scid mice, possibly in response to elevated DNA strand breaks. Cell Death and Differentiation (2001) 8, 245 ± 255.

DNA-PK promotes the survival of young neurons in the embryonic mouse retina

“…To strengthen our observations, we analyzed the retinal phenotype of a mouse model with severe combined immunodeficiency (SCID) that expresses a truncated, enzymatically inactive form of the DNA-PK catalytic subunit . 29 Although no differences were found in E14.5 retinas in the proportion of Figure 3 Induction of the DNA damage response in organotypic retinal cultures. E14.5 retinas were cultured for 6 h in the presence of etoposide (a), or for 30 min, followed by 2.5 h incubation without the drug (b-f).…”

“…Selective inhibition of DNA-PK, but not of ATM, increased caspasedependent cell death, an observation that correlates well with the phenotype of mutant mice. 16,29,32 Further, interference with DNA-PK reduced the number of young neurons, without producing a clear effect on proliferating cells, and this effect was reverted by a pan-caspase inhibitor. DNA-PK inhibition directly affected neuronal survival.…”

Genetic interaction between DNA polymerase β and DNA-PKcs in embryogenesis and neurogenesis

“…In addition, these apoptotic cells obviously increased during E9.5-E10.5. In Polb-deficient, 7 SCID 19,26 or NHEJ-deficient mice, 17,19,38,39 neuronal apoptosis has been observed in the CNS of E12.5-E16.5 mice. In this study, however, we found that in Polb We observed that apoptosis associated with Polb deficiency is mediated by the p53-dependent apoptosis pathway in the nervous system.…”

“…7,26 To examine whether similar apoptosis occurred in mice bred in this study, we performed immunohistochemical analyses on sections of the nervous system. We used anti-cleaved caspase-3 antibody to detect apoptosis and antineuron-specific type-III b-tubulin antibody to detect neuronal differentiation.…”

“…24,25 The mutant mice also exhibit slightly elevated neuronal apoptosis between the VZ and PPL at E14.5. 26,27 Taken together, it is evident that apoptosis occurs in early postmitotic, immature neurons and that NHEJ plays a crucial role in neurogenesis.…”