Spees, J.L.*; Chang, S. A..; Snyder, M. J.; Chang, E. S.: Interactive effects of osmotic and thermal stress on stress-responsive gene expression in the American lobster, Homarus americanus

Organisms in nature experience multiple environmental stressors simultaneously. For marine animals such as the American lobster, Homarus americanus, osmotic and thermal stress often occur concurrently or in close temporal proximity. Presently however, few studies have examined the molecular basis for responding to multiple stressors or whether such events can interactively alter the expression of stress-responsive genes in vivo. To this end, we first characterized the effects of hypo- and hyper-osmotic stress on the lobster for 0.5, 1, and 2 h. We quantified the expression of the molecular chaperone HSP90 (an indicator of reversible protein damage) and polyubiquitin (an indicator of irreversible protein damage) as measures of cellular perturbation in abdominal muscle and hepatopancreas (a digestive tissue). We then exposed lobsters to either a 2 h hypo- or hyper-osmotic stress followed immediately by a 2 h thermal stress and a brief recovery (3 h). Balanced design two-way ANOVA was used to detect interactions between salinity exposure and treatment time in the first experiment and to detect interactions between osmotic and thermal stress in the second experiment. Significant interactions were found between salinity exposure and treatment time for both HSP90 mRNA levels as well as polyubiquitin mRNA levels for hepatopancreas; such interactions were not observed for abdominal muscle. However, osmotic and thermal stress did interact significantly to alter the expression of both HSP90 and polyubiquitin in abdominal muscle, as well as HSP90 expression in hepatopancreas. Polyubiquitin mRNA levels in hepatopancreas, although significantly higher than control levels, did not display a significant interaction between osmotic and thermal stress.