Foci on fanconi

Fanconi anemia FANCG protein in mitigating radiation- and enzyme-induced DNA double-strand breaks by homologous recombination in vertebrate cells

The rare hereditary disorder Fanconi anemia (FA) is characterized by progressive bone marrow failure, congenital skeletal abnormality, elevated susceptibility to cancer, and cellular hypersensitivity to DNA cross-linking chemicals and sometimes other DNA-damaging agents. Molecular cloning identified six causative genes (FANCA, -C, -D2, -E, -F, and -G) encoding a multiprotein complex whose precise biochemical function remains elusive. Recent studies implicate this complex in DNA damage responses that are linked to the breast cancer susceptibility proteins BRCA1 and BRCA2. Mutations in BRCA2, which participates in homologous recombination (HR), are the underlying cause in some FA patients. To elucidate the roles of FA genes in HR, we disrupted the FANCG/XRCC9 locus in the chicken B-cell line DT40. FANCG-deficient DT40 cells resemble mammalian fancg mutants in that they are sensitive to killing by cisplatin and mitomycin C (MMC) and exhibit increased MMC and radiation-induced chromosome breakage. We find that the repair of I-SceI-induced chromosomal double-strand breaks (DSBs) by HR is decreased approximately 9-fold in fancg cells compared with the parental and FANCG-complemented cells. In addition, the efficiency of gene targeting is mildly decreased in FANCG-deficient cells, but depends on the specific locus. We conclude that FANCG is required for efficient HR-mediated repair of at least some types of DSBs.

Fanconi anemia group A and C double-mutant mice: functional evidence for a multi-protein Fanconi anemia complex

OBJECTIVE

Fanconi anemia (FA) is a genetically heterogeneous disorder associated with defects in at least eight genes. The biochemical function(s) of the FA proteins are unknown, but together they define the FA pathway, which is involved in cellular responses to DNA damage and in other cellular processes. It is currently unknown whether all FA proteins are involved in controlling a single function or whether some of the FA proteins have additional roles. The aim of this study was 1) to determine whether the FA group A and group C genes have identical or partially distinct functions, and 2) to have a better model for human FA.

MATERIALS AND METHODS

We generated mice with a targeted mutation in fanca and crossed them with fancc disrupted animals. Several phenotypes including sensitivity to DNA cross linkers and ionizing radiation, hematopoietic colony growth, and germ cell loss were analyzed in fanca-/-, fancc-/-, fanca/fancc double -/-, and controls.

RESULTS

Fibroblast cells and hematopoietic precursors from fanca/fancc double-mutant mice were not more sensitive to MMC than those of either single mutant. fanca/fancc double mutants had no evidence for an additive phenotype at the cellular or organismal level.

CONCLUSIONS

These results support a model where both FANCA and FANCC are part of a multi-protein nuclear FA complex with identical function in cellular responses to DNA damage and germ cell survival.

Disease model: Fanconi anemia

Fanconi anemia (FA) is a chromosomal instability syndrome characterized by the presence of pancytopenia, congenital malformations and cancer predisposition. Six genes associated with this disorder have been cloned, and mice with targeted disruptions of several of the FA genes have been generated. These mouse models display the characteristic FA feature of cellular hypersensitivity to DNA cross-linking agents. Although they do not develop hematological or developmental abnormalities spontaneously, they mimic FA patients in their reduced fertility. Studies using these animal models provide valuable insights into the involvement of apoptotic pathways in FA, and help characterize the defects in FA hematopoietic cells. In addition, mouse models are also useful for testing treatments for FA.