Spatial analysis of gene regulation reveals new insights into the molecular basis of upper thermal limits.
The cellular stress response has long been the primary model for studying the molecular basis of thermal adaptation, yet the link between gene expression, RNA metabolism and physiological responses to thermal stress remains largely unexplored. We address this by comparing the transcriptional and physiological responses of three geographically distinct populations of Drosophila melanogaster from eastern Australia in response to, and recovery from, a severe heat stress with and without a prestress hardening treatment. We focus on starvin (stv), recently identified as an important thermally responsive gene. Intriguingly, stv encodes seven transcripts from alternative transcription sites and alternative splicing, yet appears to be rapidly heat inducible. First, we show genetic differences in upper thermal limits of the populations tested. We then demonstrate that the stv locus does not ubiquitously respond to thermal stress but is expressed as three distinct thermal and temporal RNA phenotypes (isoforms). The shorter transcript isoforms are rapidly upregulated under stress in all populations and show similar molecular signatures to heat-shock proteins. Multiple stress exposures seem to generate a reserve of pre-mRNAs, effectively 'priming' the cells for subsequent stress. Remarkably, we demonstrate a bypass in the splicing blockade in these isoforms, suggesting an essential role for these transcripts under heat stress. Temporal profiles for the weakly heat responsive stv isoform subset show opposing patterns in the two most divergent populations. Innate and induced transcriptome responses to hyperthermia are complex, and warrant moving beyond gene-level analyses.
School of Biological Sciences, Monash University, Clayton, Vic., 3800, Australia.
Marina
M
Telonis-Scott
Allannah S
AS
Clemson
Travis K
TK
Johnson
Carla M
CM
Sgrò
D017398:Alternative Splicing; D000704:Analysis of Variance; D000818:Animals; D001315:Australia; D029721:Drosophila Proteins / Q000235:genetics* / Q000502:physiology; D004331:Drosophila melanogaster / Q000235:genetics* / Q000502:physiology; D005260:Female; D005786:Gene Expression Regulation; D014644:Genetic Variation; D005828:Genetics, Population; D018869:Heat-Shock Response / Q000235:genetics*; D006358:Hot Temperature; D010641:Phenotype; D059467:Transcriptome
D029721:Drosophila Proteins; C513903:stv protein, Drosophila
Drosophila; alternative transcript isoforms; stv; thermotolerance