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Characterization of postreplication repair in mutagen-sensitive strains of Drosophila melanogaster
Abstract:
Mutants of Drosophila melanogaster, with suspected repair deficiencies, were analyzed for their capacity to repair damage induced by X-rays and UV radiation. Analysis was performed on cell cultures derived from embryos of homozygous mutant shocks. Postreplication repair following UV radiation has been analyzed in mutant stocks derived from a total of ten complementation groups. Cultures were irradiated, pulse-labeled, and incubated in the dark prior to analysis by alkaline sucrose gradient centrifugation. Kinetics of the molecular weight increase in newly synthesized DNA were assayed after cells had been incubated in the presence or absence of caffeine. Two separate pathways of postreplication repair have been tentatively identified by mutants derived from four complementation groups. The proposed caffeine sensitive pathway (CAS) is defined by mutants which also disrupt meiosis. The second pathway (CIS) is caffeine insensitive and is not yet associated with meiotic functions. All mutants deficient in postreplication repair are also sensitive to nitrogen mustard. The mutants investigated display a normal capacity to repair single-strand breaks induced in DNA byX-rays, although two may possess a reduced capacity to repair damage caused by localized incorporation of high specific activity thymidine-3H. The data have been employed to construct a model for repair of UV-induced damage in Drosophila DNA. Implications of the model for DNA repair in mammals are discussed.
Insights
Drosophila mutants reveal two DNA repair pathways for UV damage: a caffeine-sensitive (CAS) pathway linked to meiosis and a caffeine-insensitive (CIS) pathway. These findings offer insights into DNA repair mechanisms in mammals.
Area of Science:
- Molecular Biology
- Genetics
- Radiation Biology
Background:
- DNA repair mechanisms are crucial for maintaining genomic integrity.
- Understanding these pathways is essential for comprehending cellular responses to radiation and chemical mutagens.
Purpose of the Study:
- To investigate DNA repair deficiencies in Drosophila melanogaster mutants.
- To identify and characterize pathways involved in postreplication repair after UV radiation exposure.
Main Methods:
- Analysis of cell cultures from homozygous mutant Drosophila embryos.
- UV irradiation, pulse-labeling, and dark incubation of cells.
- Alkaline sucrose gradient centrifugation to assess DNA molecular weight kinetics.
- Assay of newly synthesized DNA in the presence or absence of caffeine.
Main Results:
- Two distinct postreplication repair pathways were identified: caffeine-sensitive (CAS) and caffeine-insensitive (CIS).
- The CAS pathway involves mutants that also disrupt meiosis.
- Mutants deficient in postreplication repair are sensitive to nitrogen mustard and exhibit normal repair of X-ray-induced single-strand breaks.
Conclusions:
- A model for UV-induced DNA damage repair in Drosophila was constructed.
- The identified repair pathways provide a framework for understanding DNA repair in mammals.
- Mutations affecting DNA repair have pleiotropic effects, including impacts on meiosis.