Abstract for presentation at 11th International Congress of Human Genetics

Generation of an ATM knock in mouse with the breast-cancer susceptibility mutation, 7271T>G

  • Dr Jeremy Arnold, Queensland Institute of Medical Research, Australia
  • Dr Jean Fleming, Griffith University, Australia
  • Dr John Luff, Queensland Institute of Medical Research, Australia
  • Dr Phil Chen, Queensland Institute of Medical Research, Australia
  • Thu Nguyen, Queensland Institute of Medical Research, Australia
  • Prof Martin Lavin, Queensland Institute of Medical Research, Australia
  • Dr Graham Kay, Queensland Institute of Medical Research, Australia
  • Dr Georgia Chenevix-Trench, Queensland Institute of Medical Research, Australia

    • There is epidemiological evidence that mutations in the ATM gene may account for a proportion of breast cancers. Studies of ataxia telangiectasia and multiple-breast cancer families have found that female heterozygotes carrying the 7271T>G (V2424G) mutation have a increased risk of developing breast cancer. We have introduced the ATM 7271T>G mutation into mice in order to determine whether this increases the incidence of mammary tumours.
    The gene targeting construct was electroporated into embryonic stem (ES) cells from 129T2/SvEms mice (agouti) and stable clones selected and screened to identify targeted clones. Targeted ES cells were then injected into C57BL6/J blastocysts (black) and resulting chimeras identified by the mosaic coat colour. The chimeras were bred with C57BL6/J mice and the progeny tested for germline transmission of the targeted ATM allele. To date, germline transmission has been established from chimaeras generated from one of the targeted ES cell clones. A mixed genetic strain has been expanded and we have generated a cohort of 40 wild type, 40 heterozygous and 40 homozygous female mice to monitor tumour formation.
    Mice from the mixed genetic background have been analysed using a series of assays for A-T phenotype to ensure no unforeseen problems arose in the construction of these mice, and to investigate whether mice homozygous for this mutation display mild A-T features similar to those in humans homozygous for this mutation. So far we have established that a) male and female homozygous mice are sterile, b) splenocytes from the homozygous have reduced survival following ionizing radiation compared to wild type splenocytes, but are less sensitive than splenocytes from ATM knockout mice, c) there is oxidative stress damage in the cerebellum of homozygous mice, but not heterozygous or wild type mice, d) the ATM protein in the 7271T>G mice has reduced kinase activity and e) homozygous pups have a lower birth weight than wild type or heterozygous pups. This confirms that the knock-in 7271T>G mice do indeed have a mild A-T phenotype as was predicted, but further analyses are required to further characterise this phenotype, and in particular their tumour susceptibility.

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