Mapping Quantitative Trait Loci Underlying Circadian Light Sensitivity In Drosophila

Abstract

Despite the significant advance in our understanding of the molecular basis of light entrainment of the circadian clock in Drosophila, the underlying genetic architecture is still largely unknown. The aim of this study was to identify loci associated with variation in circadian photosensitivity, which are important for the evolution of this trait. We have used complementary approaches that combined quantitative trait loci (QTL) mapping, complementation testing and transcriptome profiling to dissect this variation.\n\nWe identified a major QTL on chromosome 2, which was subsequently fine-mapped using deficiency complementation mapping into two smaller regions spanning 139 genes, some of which are known to be involved in functions which have been previously implicated in light entrainment. Two genes implicated with the clock and located within that interval, timeless and cycle, failed to complement the QTL, indicating that alleles of these genes contribute to the variation in light response. Specifically, we find that the timeless s/ls polymorphism that has been previously shown to constitute a latitudinal cline in Europe, is also segregating in our recombinant inbred lines, and is contributing to the phenotypic variation in light sensitivity.\n\nWe have also profiled gene expression in two recombinant inbred strains that differ significantly in their photosensitivity, and identified a total of 368 transcripts that showed differential expression (FDR < 0.1). Out of 131 transcripts that showed a significant RIL by treatment interaction (i.e. putative expression QTL), four are located within QTL2