研究领域

Research focuses on how organisms (primarily fish) adapt their physiology, biochemistry and molecular biology to the environment. The emphasis is on nitrogen metabolism and excretion, particularly on the phenomenon of urea excretion by fish (e.g., toadfish and sharks). This program seeks to understand why fish sometimes produce urea (instead of ammonia) from an ecological and evolutionary perspective, and to understand the molecular mechanisms enabling shifts from ammonia to urea production and excretion. Studies of gene expression using Micro arrays will feature more prominently in the future.

1. 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. 2. Regulation of expression and evolution 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.

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Walsh, P.J., S.L. Smith, L.E. Fleming, H. Solo-Gabriele, W.H. Gerwick (Eds.). Oceans and Human Health: Risks and Remedies from the Sea. Academic Press, Amsterdam, xxiii & 644 pages, 2008 Wood, C.M., M.D. McDonald, L. Sundin, P. Laurent, P.J. Walsh. Pulsatile urea excretion in the gulf toadfish: mechanisms and control. Comp. Biochem. Physiol. 136B: 667-684, 2003 Matey, V., C.M. Wood, W. Dowd, D. Kültz, P.J. Walsh. Morphology of the rectal gland of the spiny dogfish (Squalus acanthias) shark in response to feeding. Can. J. Zool. 87: 440-452, 2009 Weihrauch, D., M.O. Wilkie, P.J. Walsh. Ammonia and urea transporters in gills of fish and aquatic crustaceans. J. Exp. Biol. 212: 1716-1730, 2009 Wilson, R.W., F.J. Millero, J.R. Taylor, P.J. Walsh, V. Christensen, S. Jennings, M. Grosell. Contribution of fish to the marine inorganic carbon cycle. Science 323: 359-362, 2009