OSOVITZ, C. J.*; HOFMANN, G. E.; University of California, Santa Barbara; University of California, Santa Barbara: Gene expression in natural populations of intertidal sea urchins on short time scales

Intertidal marine organisms often experience significant changes in environmental temperature on very short time scales, and rapid alteration in gene expression is an important compensatory mechanism in response to these fluctuating environmental conditions. We examined transcription of hsp70 in intertidal purple sea urchins, Strongylocentrotus purpuratus, in response to rapidly rising tidepool temperatures at low tide. Heat-shock protein 70 (Hsp70) is a key hsp gene expressed in response to thermal stress and functions as a molecular chaperone that ameliorates thermally-induced protein denaturation. Since transcription of Hsp genes is the earliest detectable evidence for the heat shock response (HSR), we chose to measure levels of hsp70 transcript as a means to determine the timing of environmentally-induced expression of the Hsp genes, an event that is often overlooked in ecologically relevant studies. In the field, we simultaneously measured tidepool temperatures and collected tube feet tissue from S. purpuratus at 1 h time intervals during low tide. Transcript levels of hsp70 and actin (act1) were measured using Northern analysis. Levels of hsp70 mRNA increased with increasing tidepool temperatures, whereas the housekeeping gene act1, which lacks a temperature-inducible promoter found in Hsp genes, did not. The hsp70 transcript level increased within minutes of an 8-10 °C increase in tidepool temperature, which is typical of the change in body temperature required to illicit the HSR. These data indicate that the temperature increases in tidepools during low tide were sufficient to trigger hsp70 induction in sea urchins, and that these responses are rapid and do not extend to housekeeping genes like the act1 gene. Supported by a NSF Predoctoral Research Fellowship to CJO.