Pleiotropic fitness effects of the Tre1/Gr5a region in Drosophila

The abundance of transposable elements and DNA repeat sequences in mammalian genomes raises the question whether such insertions represent passive evolutionary baggage or may influence the expression of complex traits. We addressed this question in Drosophila melanogaster where the effects of single transposable elements on complex traits can be assessed in genetically identical individuals reared in controlled environments. Here we demonstrate that single P-element insertions in the intergenic region between the Gustatory receptor 5a (Gr5a) and Trapped in endoderm 1 (Tre1), which encodes an orphan receptor, exert complex pleiotropic effects on fitness traits, including selective nutrient intake, resistance to starvation and heat stress, and life span. Mutations in this region interact epistatically with downstream components of the insulin signaling pathway. Transposon-induced sex-specific and sex-antagonistic effects further accentuate the complex influences intergenic transposable elements can contribute to complex phenotypes. Keywords: Transcriptional profiles of P-element insertion lines in the Tre1/GR5a region of Drosophila BG02514, BG02257 and Canton S (B) lines were reared simultaneously at 25 C under a 12 h light/dark cycle and 70% humidity. At 5-7 days post-eclosion, we removed the heads of two replicate groups of 100 males and 100 females for each line. Total RNA was isolated from each replicate and biotinylated cRNA probes were hybridized to high density oligonucleotide microarrays (Affymetrix, Inc.) and visualized with a streptavidin-phycoerythrin conjugate, as described in the Affymetrix GeneChip Expression Analysis Technical Manual (2000), using internal references for quantification. The quantitative estimate of expression of each probe set is the Signal (Sig) metric, as described in the Affymetrix Microarray Suite, Version 5.0. Sig values were analyzed by two-way ANOVA according to the model Y = μ + L + S + LxS + E, where L is the effect of line, S is the effect of sex and E the error variance