Pat Walsh - Research
My laboratory examines the effects of stress on fish, with stressors including ammonia, air-exposure, confinement, exercise, feeding, etc. We focus primarily on nitrogen metabolism and excretion, comparing these patterns in marine toadfish, rainbow trout, zebrafish and dogfish sharks. Our focus in the coming years will be increasingly genomic, and microarray technology will feature prominently in our research.
Major Research Interests
1. Effects of stress on gene expression in fish red blood cells
Unlike mammals, the red blood cells of fish and other lower vertebrates contain nuclei, and thus are predicted to have a greater dynamic range in gene expression. This project is using microarray approaches to determine what genes are expressed in fish red blood cells (primarily rainbow trout, toadfish, and zebrafish) and then will examine how gene expression changes with stress. For rainbow trout, we are using the GRASP array constructed for Salmonids at the University of Victoria. For toadfish, we are undertaking an Expressed Sequence Tag (EST) sequencing project and plan to fabricate toadfish-specific microarrays.
2. Responses to feeding by dogfish shark rectal gland
Following feeding, dogfish sharks and other elasmobranch fishes activate the rectal gland to secrete concentrated solutions of NaCl to rid their bodies of the salt load from feeding. Along with this activation is a tremendous activation of metabolism to support this secretion. We have noted increases in the activities of several enzymes of metabolism already. Proteomic and functional genomic studies are underway to determine more broadly what changes in gene expression occur following feeding. In vivo studies are conducted at Bamfield Marine Sciences Centre in British Columbia.
3. Ammonia toxicity in fish
In the process of looking for animal models of the human disease hepatic encephalopathy, and in attempting to understand the effects of increasing global nitrogen pollution on aquatic ecosystems, we discovered that susceptibility to ammonia toxicity in fish is highly variable. Some species (e.g., the toadfish and the Lake Magadi tilapia) are highly tolerant, whereas other species (e.g., rainbow trout and zebrafish) are markedly less tolerant. With the above background in mind, we wish to identify the genes which confer ammonia tolerance or susceptibility to fish. We plan to use existing microarrays for rainbow trout and zebrafish, and to use our own fabricated arrays for toadfish.
4. Regulation of expression of glutamine synthetase, urea transporters, and Rhesus proteins (ammonia transporters) in gulf toadfish
Toadfish use urea excretion as part of an elaborate system to confuse predators, specficially to mask the scent of their own excreted ammonia. The genes controlling the synthesis of urea (glutamine synthetase or GS) and excretion of urea (urea transporter or UT) have been shown to be induced by rises in plasma cortisol brought on by stress in the toadfish system. This project examines the role of cortisol response elements in the promoter region of the GS and UT genes in controlling their expression. Also of interest is the tissue-specificity of gene expression. Notably for GS there are two genes identified, with one specific to the gill. For UT and Rh, we wish to determine which cells within the gill express these genes. In addition to molecular methods, immunocytochemistry and in situ hybridization approaches are of use