Abstract
The embryonic ventricular and subventricular zones (VZ/SVZ) contain the neuronal stem and progenitor cells and undergo rapid proliferation. The intermediate zone (IZ) contains nonreplicating, differentiated cells. The VZ/SVZ is hypersensitive to radiation-induced apoptosis. Ablation of DNA non-homologous end-joining (NHEJ) proteins, XRCC4 or DNA ligase IV (LigIV), confers ataxia telangiectasia mutated (ATM)-dependent apoptosis predominantly in the IZ. We examine the mechanistic basis underlying these distinct sensitivities using a viable LigIV (Lig4(Y288C)) mouse, which permits an examination of the DNA damage responses in the embryonic and adult brain. Via combined analysis of DNA breakage, apoptosis, and cell-cycle checkpoint control in tissues, we show that apoptosis in the VZ/SVZ and IZ is activated by low numbers of DNA double-strand breaks (DSBs). Unexpectedly, high sensitivity in the VZ/SVZ arises from sensitive activation of ATM-dependent apoptosis plus an ATM-independent process. In contrast, the IZ appears to be hypersensitive to persistent DSBs. NHEJ functions efficiently in both compartments. The VZ/SVZ and IZ regions incur high endogenous DNA breakage, which correlates with VZ proliferation. We demonstrate a functional G(2)/M checkpoint in VZ/SVZ cells and show that it is not activated by low numbers of DSBs, allowing damaged VZ/SVZ cells to transit into the IZ. We propose a novel model in which microcephaly in LIG4 syndrome arises from sensitive apoptotic induction from persisting DSBs in the IZ, which arise from high endogenous breakage in the VZ/SVZ and transit of damaged cells to the IZ. The VZ/SVZ, in contrast, is highly sensitive to acute radiation-induced DSB formation.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Age Factors
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Animals
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Animals, Newborn
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Apoptosis / genetics
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Apoptosis / physiology
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Apoptosis / radiation effects
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Ataxia Telangiectasia Mutated Proteins
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Bromodeoxyuridine / metabolism
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Cell Cycle / genetics
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Cell Cycle Proteins
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Cell Proliferation / radiation effects
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Cerebral Ventricles / cytology*
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Cerebral Ventricles / embryology*
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Cerebral Ventricles / radiation effects
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Chromosomal Proteins, Non-Histone / metabolism
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Cysteine / genetics
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DNA Breaks, Double-Stranded / radiation effects
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DNA Ligase ATP
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DNA Ligases / genetics
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DNA Ligases / metabolism*
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DNA-Binding Proteins / deficiency
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DNA-Binding Proteins / metabolism
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Embryo, Mammalian
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Embryonic Development* / genetics
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Embryonic Development* / physiology
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Gene Expression Regulation, Developmental / genetics
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Gene Expression Regulation, Developmental / radiation effects
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Histones / metabolism
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In Situ Nick-End Labeling / methods
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Mice
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Mice, Inbred C57BL
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Mice, Transgenic
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Models, Biological
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Mutation / genetics
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Neural Stem Cells / physiology
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Neural Stem Cells / radiation effects
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Neurons / physiology*
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Neurons / radiation effects
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Protein Serine-Threonine Kinases / deficiency
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Radiation, Ionizing
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T-Box Domain Proteins / metabolism
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Tubulin / metabolism
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Tumor Suppressor Proteins / deficiency
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Tumor Suppressor p53-Binding Protein 1
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Tyrosine / genetics
Substances
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Cell Cycle Proteins
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Chromosomal Proteins, Non-Histone
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DNA-Binding Proteins
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Eomes protein, mouse
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Histones
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T-Box Domain Proteins
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Trp53bp1 protein, mouse
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Tubulin
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Tumor Suppressor Proteins
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Tumor Suppressor p53-Binding Protein 1
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beta3 tubulin, mouse
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Tyrosine
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Ataxia Telangiectasia Mutated Proteins
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Atm protein, mouse
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Protein Serine-Threonine Kinases
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DNA Ligases
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DNA Ligase ATP
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Bromodeoxyuridine
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Cysteine