Gamma-irradiation stimulates homology-directed DNA double-strand break repair in Drosophila embryo.

To test the DNA double-strand break (DSB) repair activities present in Drosophila early embryos, we have analyzed the circularization of a microinjected linear plasmid. In order to study repair by homologous recombination, the linear plasmid was injected with an homologous fragment encompassing the break. After extraction from embryos, repair products were analyzed directly by PCR and after their cloning into bacteria. We demonstrate, in addition to the repair by homologous recombination, the presence of an efficient end-joining activity in embryos. Plasmid circularization by end-joining was accompanied by short deletions frequently associated with non-random insertions. Most importantly, pre-irradiation of embryos specifically enhanced the accurate repair by homologous recombination. Such a stimulation is described for the first time in the context of a whole higher organism.