Hematopoietic dysfunction in a mouse model for Fanconi anemia group D1.

We have investigated the hematopoietic phenotype of mice with a hypomorphic mutation in the Brca2/Fancd1 gene (Brca2(Delta27/Delta27) mutation). In contrast to observations made in other Fanconi anemia (FA) mouse models, low numbers of hematopoietic colony-forming cells (CFCs) were noted in Brca2(Delta27/Delta27) mice, either young or adult. Additionally, a high incidence of spontaneous chromosomal instability was observed in Brca2(Delta27/Delta27) bone marrow (BM) cells, but not in Brca2(+/Delta27) or Fanca(-/-) BM cells. Although Brca2(Delta27/Delta27) CFCs were not hypersensitive to ionizing radiation, a very severe hematopoietic syndrome was observed in irradiated Brca2(Delta27/Delta27) mice. Conventional BM competition experiments showed a marked repopulation defect in Brca2(Delta27/Delta27) hematopoietic stem cells (HSCs), compared to wild-type HSCs. Moreover, we have observed for the first time in a DNA repair disease model a very significant proliferation defect in Brca2(Delta27/Delta27) HSCs maintained in their natural physiological environment. The progressive repopulation of wild-type HSCs transplanted into unconditioned Brca2(Delta27/Delta27) recipients is reminiscent of the somatic mosaicism phenomenon observed in a number of genetic diseases, including FA. The hematopoietic phenotype associated with the Brca2(Delta27/Delta27) mutation suggests that this FA-D1 mouse model will constitute an important tool for the development of new therapies for FA, including gene therapy.