Loss of RecQ5 leads to spontaneous mitotic defects and chromosomal aberrations in Drosophila melanogaster

RecQ5 belongs to the RecQ DNA helicase family that includes genes causative of Bloom, Werner, and Rothmund-Thomson syndromes. Although no human disease has been genetically linked to a mutation in RecQ5, Drosophila melanogaster RecQ5 is highly expressed in early embryos, suggesting an important role for it in the DNA metabolism of the early embryo. In this present study, we generated RecQ5 mutants in D. melanogaster. Embryos lacking maternally derived RecQ5 contained irregular nuclei in early embryogenesis. These irregular nuclei emerged in nuclear cycle 11-13, lost cell-cycle markers, and were located below the surface monolayer of nuclei. By time-lapse microscopy, these irregular nuclei were observed not to divide, whereas all neighboring nuclei proceeded through normal mitotic division with synchrony. These data suggest that the irregular nuclei exited from the nuclear division cycle. This phenotype is reminiscent of the effect of X-ray irradiation on wild-type embryos and was rescued by expression of RecQ5. Thus, the maternal supply of RecQ5 is important for the nuclear cycles in syncytical embryos. Furthermore, the frequencies of spontaneous and induced chromosomal aberrations were increased in RecQ5 mutant neuroblasts. These data imply that DNA damage accumulates spontaneously in RecQ5 mutants. Therefore, endogenous genomic damage may be produced in Drosophila development, and RecQ5 would be involved in the maintenance of genomic stability by suppressing the accumulation of DNA damage.

Relationships of Drosophila melanogaster RECQ5/QE to cell-cycle progression and DNA damage

Members of the RecQ family of DNA helicases are involved in the cellular response to DNA damage and are regulated in the cell-cycle. However, little is known about RecQ5, one of these members. The level of RECQ5/QE, Drosophila melanogaster RecQ5, was increased after the exposure of cultured cells to methyl-methanesulfonate. Transgenic flies that overexpressed RECQ5/QE in their developing eye primordia showed mild roughening of the ommatidial lattice. DNA-damaging agents and the mei-41 mutation enhanced the phenotype caused by RECQ5/QE overexpression. Overexpression of RECQ5/QE perturbed the progression of the cell-cycle in response to DNA damage in the eye imaginal discs. These results suggest that RECQ5/QE interacts with components of the cell-cycle during its progression in response to DNA damage.