Molecuilar Physiology of Stress Tolerance in Marine Invertebrates: The Heat Shock Response and Multidrug Resistance
A number of molecular mechanisms have been implicated in biological tolerance of marine environmental stress. Among the best characterized of these is the heat shock response, which has been shown to play an important role in determining the distribution of marine invertebrates along natural gradients of stress (eg. thermal stress in the intertidal). The heat shock response also appears to play a critical role in determining the susceptibility of invertebrates to anthropogenic stress. In a parallel context, it has been proposed that multidrug resistance may play an important role in determining the survival of invertebrates along natural and anthropogenic gradients of toxic organic compounds.
This study characterized the role of both of these systems in the tolerance of natural stressors in model marine invertebrate systems. ln the first section of the dissertation I demonstrated that, although Pacific oysters are capable of significant adaptive regulation of heat shock protein (HSP) expression, adaptive plasticity occurs at a physiologic cost to inducible stress tolerance. Moreover. although adaptive regulation of HSPs is via a transcriptional mechanism during conditions of acute thermal stress. the response to chronic stress may not require continual transcriptional activation of HSP genes. ln the second section of the dissertation I focused on the role ofmultidrug resistance (MDR) transporters in oocytes. embryos and larvae in model (sea urchin, starfish and urechis) systems. In the first chapter of this section l described species-specific differences in transporter expression and consequent differences in susceptibility to naturally degraded hydrocarbons. In the second chapter I hypothesized that the reason for organic susceptibility in echinoderms is not due to the absence of a transporter. but rather due to the specificity of the predominant transporter family expressed in each species. Consistent with this hypothesis I showed that the predominant type of transporter expressed in echinoderm oocytes and embryos bear homology to the multidrug resistance associated protein (MRP) family rather than the multidrug resistance (P-gp/MDR) family. I examined the potential consequences of this difference for transporter substrate specificity and we measured the level of MRP expression during early development. I show that echinoderms possess a characteristic MRP transport phenotype that is activated at fertilization.