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Title: ENU mouse mutant with a hypomorphic mutation in DNA ligase IV
Author: Nijnik, A.
ISNI:       0000 0001 3446 9040
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2006
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This thesis describes the generation, mapping, and characterisation of a mutant mouse strain derived from a genome-wide ENU mutagenesis programme in collaboration between Australian National University and Oxford University funded by the Wellcome Trust. Starting with the identification of the growth retardation and immunodeficiency phenotype in the G3 progeny of one mutagenised mouse, we mapped the mutation to the DNA Ligase IV (LigIV) gene. The enzyme is the final component of the nonhomologous end joining (NHEJ) pathway of DNA double strand break repair, which is involved in maintenance of genomic stability and in VDJ rearrangement of lymphocyte receptor genes. The mutation is a single base change that results in a Y288C amino acid substitution near the active site of the LigIV enzyme. The mutation causes an over 20- fold reduction in the LigIV enzymatic activity in vivo, partly though its effect on protein stability and expression levels. This mouse strain is the first viable animal model of LigIV deficiency, and therefore this work contributes to our understanding of the pathology of the human LigIV syndrome. Here we provide a detailed characterisation of the strain, addressing a number of questions about the physiological pathways in which LigIV activity is limiting. Lymphocyte development is impaired in the mutants and peripheral lymphocyte numbers are reduced nearly 100-fold, but a population of B1 cells develops in the peritoneal cavity. In addition to impaired VDJ rearrangement, lymphocyte survival in peripheral lymphoid organs is also affected by the mutation and this may contribute to the lymphopenia. We also demonstrate that LigIV is required for normal immunoglobulin class switching. Furthermore, the mutant bone marrow is deficient in reconstituting haematopoiesis in irradiated recipients and we observe an age-dependent decline in the stem and progenitor cell population in the bone marrow of the mutant mice, suggesting that LigIV activity may also be limiting in the maintenance and function of haematopoietic stem cells. In addition, the mutant mice are highly predisposed to haematopoietic malignancies. This demonstrates how ENU mutagenesis can be used to create hypomorphic alleles of genes essential for survival, contributing to our understanding of the function of mammalian genes and creating animal models of human genetic diseases.
Supervisor: Cornall, Richard John Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Mice ; Abnormalities ; Genetic aspects ; DNA ligases ; Mutagenesis