Date of Award

Spring 2008

Project Type

Dissertation

Program or Major

Animal and Nutritional Sciences

Degree Name

Doctor of Philosophy

First Advisor

Samuel C Smith

Abstract

Representational Difference Analysis (RDA) was used to identify genes that were differentially expressed between White Carneau (WC) and Show Racer (SR) pigeon aortic smooth muscle cells. The gene(s) responsible for atherosclerotic resistance in cultured SR smooth muscle cells (SMC) were hypothesized to be silent or down regulated in the WC. In the reciprocal experiments, it was hypothesized that the gene(s) contributing to the spontaneous atherosclerotic phenotype in cultured WC SMC would not be expressed in the SR.

Total RNA was extracted from primary cultured cells of each breed, converted to cDNA, and compared in four reciprocal RDA experiments. Seventy-four transcripts were identified exclusively in the WC cells, and 63 were unique to the SR. Genes representing several biochemical pathways were distinctly different between aortic cells from susceptible (WC) and resistant (SR) pigeons.

The most striking genetic differences were observed in energy metabolism and smooth muscle contractility. The WC cells derived their energy from glycolysis, while the SR cells utilized oxidative phosphorylation to produce energy. Myosin light chain kinase and alpha actin were exclusively expressed by the SR SMC, whereas beta actin and collagen were dominant in the WC. Because of the compressed in vitro time frame compared with in vivo development, it was not obvious whether insufficient ATP synthesis is preventing the WC aortic cells from performing their contractile function or if the lack of functional contractile elements in the WC causes the mitochondrial ATP synthesis to down regulate. Either way, energy production was successfully coupled to muscle contraction in the SR, but not in the WC. This difference was observed prior to lipid accumulation in the WC cells, and appears to be a major contributing factor in pigeon atherogenesis.

One hundred forty five pigeon transcripts were homologous to the chicken. However, the mitochondrial genes expressed in the pigeon were more closely related to non-domestic birds such as the turkey vulture and oriental stork. Despite this categorical exception, the recently published chicken genome was an ideal resource for identifying differentially expressed genes in the pigeon. The results were interpreted in the context of current hypotheses of human atherogenesis. The pigeon transcripts can also be used in comparative studies of avian genomics.

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