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3258 TAMU Office: Lab: Fax: 979-845-2891 |
Biography |
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Duncan MacKenzie joined the Department of Biology as an Assistant Professor in September of 1983 and was promoted to Associate Professor in 1989. He currently serves as Director of the departmental BioAquatics Facility. In the past he has served as the Graduate Advisor in Biology (1993-1998) and as Chair of the University Laboratory Animal Care Committee (1998-2002). Prior to coming to Texas A&M, he earned a B.S. in Zoology (1975) from the University of California, Davis. In 1980, he earned a Ph.D. in Zoology (1980) from the University of California, Berkeley, working with Dr. Paul Licht on the regulation of thyroid function and reproduction in nonmammalian vertebrates. He continued research on the regulation of thyroid function in fish as a postdoctoral fellow in the laboratory of Dr. R. E. Peter at the University of Alberta. Duncan MacKenzie's primary research interests focus on the regulation of growth and reproduction in nonmammalian vertebrates. This has included work on the purification and characterization of thyrotropins and gonadotropins from reptiles, amphibians, and fish, as well as examination of the interactions between the thyroid, reproductive, and somatotropic endocrine systems in fish. He currently studies the seasonal and daily regulation of thyroid hormone production in fish and reptiles. He teaches undergraduate courses in comparative physiology, comparative endocrinology, and human anatomy and physiology, as well as a graduate course and seminars in comparative endocrinology. |
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| Comparative Endocrinology of Thyroid Function | |
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Hormones secreted by the thyroid gland are of primary importance in the regulation of such fundamental physiological processes as growth, nutrient utilization, and reproduction. In my laboratory, we examine the regulation of the secretion of thyroid hormones and their actions in poikilothermic vertebrates in order to understand the evolution of thyroid function. We are presently focusing on the relationship between nutrient intake and thyroid hormone secretion in commercially-important fish species such as the red drum (Sciaenops ocellatus) and the channel catfish (Ictalurus punctatus). We have demonstrated that both quantity and quality of food intake alter the production of thyroid hormones, and that thyroid hormone administration has significant effects on the metabolism of protein and lipid. Changes in blood protein composition associated with nutrient mobilization for reproduction also alter thyroid hormone delivery to target cells. We have recently discovered that blood thyroxine levels undergo robust daily cycles in the red drum, supporting a role for an endogenous clock in the central control of thyroid hormone production. Future studies will be directed towards examining the regulation of thyroid hormone cycles and determining their physiological significance. I also intend to examine the specific mechanisms through which nutrient intake influences thyroid hormone secretion, and the manner in which thyroid hormone delivery to target tissues is influenced by circulatory factors unique to poikilotherms. A comparative perspective is always maintained in my research. Because of their position at the transition to endothermy, reptiles remain an interesting model for the examination of thyroid hormone action. For this reason, I also direct research on endocrine function in reptiles, such as sea turtles, desert tortoises, and alligators. From these animals we gain a broader perspective of the relationship between nutrient intake, temperature, and thyroid hormone production. This research is aimed at providing new insights into the potentially ancient role of thyroid hormones in nutrient assimilation, as well as elucidating evolutionary trends in the regulation of thyroid function. These studies may serve identify ways in which the pituitary-thyroid axis may be manipulated to enhance aquaculture production or endangered species conservation. |
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| Selected Publications | |
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Valverde, R.A., Stabenau,, E.K., and MacKenzie, D.S. (2007) Respiratory and endocrine physiology. In: Biology and Conservation of Ridley Sea Turtles, Plotkin, P., ed. The Johns Hopkins University Press. pp. 119-150. Loter, T.C., MacKenzie, D.S., McLeese, J., and Eales, J.G. (2006) Seasonal changes in channel catfish thyroid hormones reflect increased magnitude of daily thyroid hormone cycles. Aquaculture 262:451-460. Mora, M.A., Musquiz, D. Bickham, J.W., MacKenzie D.S., Hooper, M.J., Szabo, J.K., and Matson, C.W. (2006). Biomarkers of exposure and effects of environmental contaminants on swallows nesting along the Rio Grande, Texas, USA. Environmental Toxicology and Chemistry 25:1574-1584. Raine, J.C., Cameron, C., Vijayan, M.M., MacKenzie, D.S., Leatherland, J.F. (2005). Effect of fasting on thyroid hormone levels and TRa and TRß mRNA accumulation in late-stage embryo and juvenile rainbow trout, Oncorhynchus mykiss. Comparative Biochemistry and Physiology, Part A 140: 452-459. Leiner. K.A., and MacKenzie. D.S. (2003) Central regulation of thyroidal status in teleost fish: Nutrient stimulation of T4 and negative feedback of T3. Journal of Experimental Zoology 298A:32-43. MacKenzie. D.S. (2002). Current status of tarpon research and future tarpon research: opportunities and needs. Contributions in Marine Science 35:112-115. Leiner, K.A. and D.S. MacKenzie. 2001. The effects of photoperiod on growth rate and circulating thyroid hormone levels in the red drum, Sciaenops ocellatus: evidence for a free-running rhythm of T4 secretion. Comp. Biochem. Physiol. 130A: 141-149. Gaylord, T.G., D.S. MacKenzie, and D.M. Gatlin. 2001. Growth performance, body composition, and plasma thyroid hormone status of channel catfish (Ictalurus punctatus) in response to short-term feed deprivation and refeeding. Fish Physiol. Biochem. 24: 73-79. VanPutte, C.L.M., D.S. MacKenzie, and J.G. Eales. 2001. Characterization of hepatic low-KM outer-ring deiodination in laboratory-reared and adult wild red drum (Sciaenops ocellatus). Comp. Biochem. Physiol. 128B: 413-423. Kohel, K.A., D.S. MacKenzie, D.C. Rostal, J.C. Grumbles, and V.A. Lance. 2001. Seasonality in plasma thyroxine in the desert tortoise, Gopherus agassizii. Gen. Comp. Endocrinol. 121: 214-222. Leiner, K.A., G.S. Han, and D.S. MacKenzie. 2000. The effects of photoperiod and feeding on the diurnal rhythm of circulating thyroid hormones in the red drum, Sciaenops ocellatus. Gen. Comp. Endocrinol. 120: 88-98. Craig, S.R., D.S. MacKenzie, G. Jones and D.M. Gatlin. 2000. Seasonal changes in the reproductive condition and body composition of free-ranging red drum (Sciaenops ocellatus). Aquaculture 190: 89-102. |
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