The role of the hsr-omega gene in adaptation to thermal stress in Drosophila melanogaster

The hsr-omega gene of Drosophila is a non-coding RNA gene that is constitutively expressed in almost all tissues of both larvae and adult Drosophila, and upon exposure to stress such as heat shock, and in the presence of various chemicals, levels of the hsr-omega transcripts are rapidly up-regulated. While hsr-omega has been studied in detail for many years and mutations in the gene have diverse phenotypic effects, its precise function in the cellular stress response and the nature of its contribution to thermal stress tolerance remains elusive. It is postulated that the hsr-omega transcripts, omega-n (nuclear) and omega-c (cytoplasmic), aid in coordinating nuclear and cytoplasmic activities such as translation, particularly during heat stress (Pardue et al., 1990). More recently, and consistent with this postulation, a model for omega-n function during heat stress has been presented by Prasanth et al. (2000), where levels of the omega-n transcript are shown to influence the nuclear localisation and availability of several heterogeneous ribonucleoprotein particles (hnRNPs) involved in RNA processing. Substantial evidence suggests that both sequence variation in the hsr-omega gene and variation in levels of its transcripts contribute to the differences in heat and cold tolerance that occur in natural populations of Drosophila melanogaster. To better understand the role of hsr-omega in thermal stress adaptation, I sought to identify a link between natural variation in functional levels of the hsr-omega transcripts and rates of general protein synthesis with and without heat exposure, in a set of lines derived from a natural population. I found evidence to support a relationship between omega-n abundance and translational ability in these lines, consistent with the proposed cellular model for omega-n function. While protein synthesis rates were not related to life-history traits, significant and repeatable associations were identified with a measure of heat tolerance, suggesting factors 5 affecting protein synthesis rates may underlie natural variation in heat tolerance in this species.