Fanconi Anemia Complementation Group D2 (fancd2) knockout mice display microphthalmia and an increased susceptibility to breast and ovarian cancer. S. Houghtaling1, C. Timmers1, S. Meyn2, M. Noll1, C. Reifsteck1, S. Olson1, S. Jones4, M. Finegold3, M. Grompe1. 1) Dept of Mol and Med Gen, OHSU, Portland, OR; 2) Dept of Mol and Med Gen, Univ of Toronto, Toronto, Canada; 3) Dept of Path, Baylor College of Medicine, Houston, TX; 4) Umass, Worcester, MA.
Fanconi anemia (FA) is an autosomal recessive disorder characterized by bone marrow failure, congenital birth defects, and an increased incidence of cancer. At least 7 complementation groups exist and recently BRCA2 has been identified as a member of the FA pathway. FANCD2 has been shown to act distally to the other FA proteins and is mono-ubiquitinated during S-phase and following DNA damage. This results in its co-localization in nuclear foci with BRCA1 and RAD51 and suggests that the FA pathway may control homologous recombination during S-phase. To further investigate the in vivo function of the FA pathway we have disrupted fancd2 by homologous recombination. Fancd2 -/- mice display phenotypes not observed in other FA knockout mice. In the C57/Bl6 background 80% of mutant mice have microphthalmia. Fancd2 -/- mice also display a more severe decrease in germ cell number than fanca, c, or g -/- mice. In addition mispairing of chromosomes during pachytene of meiosis was seen. Significantly, 2/5 female fancd2 -/- mice older than 14 months had breast or ovarian cancer. Similar to FA patients and other FA mouse models, fancd2 -/- mice exhibit in vivo ionizing radiation (IR) sensitivity and cellular sensitivity to DNA crosslinking agents. FANCD2 was recently reported to be a substrate of the ATM kinase and implicated in controlling an S-phase checkpoint in response to IR. Therefore, primary fancd2 -/- fibroblasts were tested for the presence of radio-resistant DNA synthesis (RDS), a measure of this S-phase checkpoint. Fancd2 -/- cells did not display RDS and thus we conclude that FANCD2 is not essential for the S-phase checkpoint in primary cells and that the modest IR sensitivity of fancd2 -/- cells is not due to defective ATM signaling. Overall, the phenotype of fancd2-/- mice supports the hypothesis that the FA proteins (including BRCA2) and BRCA1 participate in a common S-phase specific DNA damage response pathway.