Fanconi Anemia (FA) is a genomic instability syndrome characterized by bone marrow failure and an increased risk of malignancy. At least 7 complementation groups (designated A-G) with similar phenotypes have been identified. Many of the genes encoding these complementation types have recently been isolated, yet their precise cellular function remains elusive. The chromosomal breaks and the cell cycle arrest observed in FA patients following treatment with clastogenic agents (mitomycin c or diepoxybutane) indirectly implicates an abnormality in cell cycle control and/or DNA repair. We utilized the murine model for FANCC (Fancc), originally developed in the laboratory of Dr. Manuel Buchwald, as an approach to examine the role of Fancc in cell cycle control. An important aspect of cell cycle control is the induction of checkpoints which enables cells to exit the cell cycle following DNA damage. We hypothesize that the genomic instability observed in Fancc cells could be the result of a damage-induced checkpoint(s) that do not function properly in these cells. We isolated murine embryonic fibroblasts from Fancc -/- and Fancc +/+ littermates. In preliminary experiments, we demonstrated that Fancc -/- MEFs had a similar hypersensitivity to MMC as previously observed in Fancc -/- cells. Since ionizing radiation is known to induce cell cycle checkpoint controls in normal cells at both Gl and G2, we conducted cell cycle analyses to examine the phenotype of Fancc -/- MEFs following irradiation. Wildtype MEFs had a marked decrease in cell proliferation following irradiation as expected, whereas irradiated Fancc -/- MEFs retained a DNA synthesis comparable to nonkradiated Fancc -/- cells, supporting a role for Fancc in damage checkpoint control. This notion was further supported by experiments demonstrating that, in the presence of ionizing radiation, Fancc -/- cells had a higher mitotic index. To further test our hypothesis, pulse BrdU labelling experiments were conducted to evaluate the proportion of cells that proceed through G2/M following irradiation. Significantly more Fancc -/- cells proceeded through G2/M following irradiation as compared to Fancc +/+ cells. These data implicate Fancc in cell cycle control in response to ionizing radiation, and Fancc -/- cells may be defective in G2 checkpoint arrest allowing cells to enter mitosis in the presence of damage.
|Original language||English (US)|
|Issue number||11 PART I|
|State||Published - Dec 1 2000|
ASJC Scopus subject areas
- Cell Biology