Differential expression of stress candidate genes for thermal tolerance in the sea urchin Loxechinus albus

Marine ectotherms inhabiting intertidal and shallow subtidal environments are continuously exposed to diurnal tidal cycles and seasonal variability in temperature. These organisms have adaptive mechanisms to maintain cellular homeostasis, irrespective of thermal environmental variation. In this study, we describe the molecular responses to thermal stress in the edible sea urchin Loxechinus albus. In particular, we determined the differential expression of a set of molecular markers that have been identified as targets of stress-related responses. These include the heat shock proteins (hsp70 and hsp90), cell detoxification proteins (cytochrome P450), and osmorregulatory proteins (a and beta-Na+/K+ ATPase). We exposed individuals to different temperatures; a warm treatment (18 +/- 1.0 degrees C), a cold treatment (10 1.0 degrees C), and a control treatment (average local temperature of 14 +/- 1.0 degrees C) and differential expression was quantified after 2, 6, 12 and 48 h of exposure. Levels of mRNA were quantified by reverse transcription-quantitative polymerase chain reaction, and the relative expression of each gene was calculated using the 18S rRNA gene as a reference, and the control treatment as a calibrator. We found that the expression levels of all studied genes increased during exposure to warmth. The largest increase in expression was observed in cytochrome p450 genes (ca. sixteen-fold); this was followed by increases in the expression of the Na+/K+ ATPase (ca. eight-fold) and by the lisp (ca. six fold) genes. These results indicate that sea urchin thermal stress responses depend on differential gene-regulation, involving heat-shock, membrane potential, and detoxification genes that generate an integrated adaptive response to acute environmental changes.