RESUMO
XLF/Cernunnos is a component of the ligation complex used in classical non-homologous end-joining (cNHEJ), a major DNA double-strand break (DSB) repair pathway. We report neurodevelopmental delays and significant behavioral alterations associated with microcephaly in Xlf-/- mice. This phenotype, reminiscent of clinical and neuropathologic features in humans deficient in cNHEJ, is associated with a low level of apoptosis of neural cells and premature neurogenesis, which consists of an early shift of neural progenitors from proliferative to neurogenic divisions during brain development. We show that premature neurogenesis is related to an increase in chromatid breaks affecting mitotic spindle orientation, highlighting a direct link between asymmetric chromosome segregation and asymmetric neurogenic divisions. This study reveals thus that XLF is required for maintaining symmetric proliferative divisions of neural progenitors during brain development and shows that premature neurogenesis may play a major role in neurodevelopmental pathologies caused by NHEJ deficiency and/or genotoxic stress.
Assuntos
Enzimas Reparadoras do DNA , Proteínas de Ligação a DNA , Humanos , Animais , Camundongos , Enzimas Reparadoras do DNA/metabolismo , Proteínas de Ligação a DNA/metabolismo , Reparo do DNA , Quebras de DNA de Cadeia Dupla , Reparo do DNA por Junção de Extremidades , Encéfalo/metabolismoRESUMO
We have previously described the identification of Artemis, a factor involved in the nonhomologous end joining (NHEJ) phase of V(D)J recombination of T and B cell receptor genes. Null mutations of the Artemis gene result in a complete absence of T and B lymphocytes that is associated with increased cell radiosensitivity, causing the radiosensitive T(-)B(-) SCID (RS-SCID) condition. We presently report the occurrence of hypomorphic mutations of the Artemis gene in four patients from two kindreds. Partially preserved in vivo activity of Artemis is associated with the presence of polyclonal T and B lymphocyte populations, albeit in reduced numbers, along with chromosomal instability and development of EBV-associated lymphoma in two of four patients. This syndrome emphasizes the role of Artemis in the NHEJ pathway of DNA repair and suggests that other, yet ill-defined, conditions associating immunodeficiency and lymphoma could be caused by mutations in genes encoding NHEJ factors.
Assuntos
Linfócitos B/imunologia , Predisposição Genética para Doença , Síndromes de Imunodeficiência/imunologia , Linfoma/etiologia , Mutação , Proteínas Nucleares , Linfócitos T/imunologia , beta-Lactamases/genética , Adolescente , Southern Blotting , Criança , Pré-Escolar , Proteínas de Ligação a DNA , Endonucleases , Saúde da Família , Feminino , Fibroblastos/metabolismo , Citometria de Fluxo , Humanos , Imuno-Histoquímica , Síndromes de Imunodeficiência/genética , Lactente , Linfoma de Células B/genética , Masculino , Reação em Cadeia da Polimerase , Imunodeficiência Combinada Severa/genética , Fatores de TempoRESUMO
B and T lymphocytes are exposed to various genotoxic stresses during their life, which originate from programmed molecular mechanisms during their development and maturation or are secondary to cellular metabolism during acute phases of cell proliferation and activation during immune responses. How lymphocytes handle these multiple genomic assault has become a focus of interest over the years, perhaps beginning with the identification of the murine scid model in the early 80s when it was recognized that DNA repair deficiencies had profound consequences on the immune system. In this respect, the immune system represents an ideal model to study DNA damage responses (DDR) and the survey of immune deficiency conditions in humans or the development of specific animal models provided many major contributions in our understanding of the various biochemical pathways at play during DDR in general. Although the role of DNA repair in the early phases of B and T cell development has been analyzed thoroughly, the role of these functions in various aspects of the mature immune system (homeostasis, immunological memory, ageing) is less well understood. Lastly, the analysis of DNA repair in the immune system has provided many insights in the more general understanding of cancer.
Assuntos
Reparo do DNA/imunologia , Rearranjo Gênico , Sistema Imunitário/fisiologia , Linfócitos/imunologia , Modelos Imunológicos , Animais , Genes de Imunoglobulinas , Humanos , VDJ RecombinasesRESUMO
The RAG1 and RAG2 proteins are the lymphoid-specific factors essential for V(D)J recombination, the process that leads to the diversification of antigen receptors on B and T lymphocytes. Nucleolar/nuclear localization of RAG1 is mediated by four basic domains, which are the binding sites for the nuclear transport proteins SRP1 and RCH1, and by a nuclear localization signal (NLS) in the fifth basic domain. The C-terminal region of RAG2 from amino acids (aa) 417 to 484 shows a homology with the PHD domain of other proteins involved in chromatin-mediated gene regulation by protein-protein interactions. Mutations in this domain were shown to be responsible for several diseases and in some case lead to altered subcellular localization of proteins. We found that the C-terminal PHD domain of RAG2 is not responsible for the nuclear localization of the protein. We report here the characterization of a region (aa 491-527) in the C-terminal domain of RAG2, downstream of the putative PHD domain, which directs the nuclear localization of the protein.