Sciara coprophila larvae upregulate DNA repair pathways and downregulate developmental regulators in response to ionizing radiation

Robust DNA damage prevention and repair strategies are crucial to faithful reproduction and inheritance of the genetic material. Although many molecular pathways that respond to DNA damage are well conserved through evolution, the quality and effectiveness of these systems can vary between species. Studies dating back for nearly a century document that the dark-winged fungus gnat Sciara coprophila (Order: Diptera; sub-order: Nematocera) is relatively resistant to irradiation-induced mutations that cause visible phenotypes when compared to the fruit fly Drosophila melanogaster (Order: Diptera; sub-order: Brachycera). However, the molecular responses to irradiation for S. coprophila have yet to be analyzed. To address this gap, we first characterized the effects of ionizing radiation on S. coprophila throughout its life cycle. Our data show that developing S. coprophila embryos are highly sensitive to even low doses of gamma-irradiation, whereas larvae can tolerate up to 80 Gy and still retain their ability to develop to adulthood with a developmental delay of 5 to 8 extra days in the larval stage. To survey the genes involved in the early transcriptional response to irradiation, we compared RNA-seq profiles of larvae with and without radiation treatment. Our analysis showed that 327 genes are differentially expressed in irradiated larvae, with 232 genes upregulated and 95 genes downregulated relative to controls. The upregulated genes were enriched for DNA damage response genes, including those involved in DNA repair, cell cycle arrest, and apoptosis, whereas the down-regulated genes were enriched for developmental regulators, consistent with the developmental delay observed in irradiated larvae. Thus, our study has laid the groundwork to further dissect how Sciara copes with radiation-induced damage.