Thermal history-dependent expression of the hsp70 gene in purple sea urchins: Biogeographic patterns and the effect of temperature acclimation

Thermal variation associated with large spatial scales is thought to significantly affect the physiology of organisms in marine systems and consequently limit their distribution. To examine this phenomenon, this study compared the heat shock protein (hsp70) mRNA expression of purple sea urchins (Strongylocentrotus purpuratus) collected from different geographic locations and those acclimated to different temperatures. Tube feet were removed from S. purpuratus freshly collected from Fogarty Creek, Oregon (FC-OR) and Carpinteria, California (CRP-CA) and from urchins acclimated to 5 °C and 20 °C in the laboratory. Tissue samples were then immediately frozen or incubated at various temperatures between 5 °C and 36 °C for 30 min in vitro. Real-time PCR was used to measure the hsp70 mRNA levels of each sample. The results showed evidence for differential regulation of hsp70 between S. purpuratus in both field and laboratory studies. For example, the incubation temperature that induced maximum hsp70 mRNA expression (Tmax) was higher in CRP-CA urchins (26 °C) than those from FC-OR (23 °C). Additionally, although the Tmax of the two acclimation groups was identical (26 °C), S. purpuratus acclimated to 5 °C failed to induce hsp70 mRNA after incubation at 32 °C, while tube feet of the 20 °C-acclimated urchins remained transcriptionally active. In general, the extent of hsp70 mRNA induction was substantial, exceeding 250-fold in the 5 °C-acclimated urchin tissues after incubation at 26 °C. These data suggest that the thermal variation encountered across S. purpuratus' range is sufficient to effect the regulation of thermally sensitive genes, like hsp70.