Date of Award

6-2011

Document Type

Open Access

Degree Name

Bachelor of Science

Department

Biology

First Advisor

Nicole Theodosiou

Language

English

Keywords

organ, physiology, colon, genes, development, evolution

Abstract

During the transition of animals from water onto land, the colon is believed to have evolved as an essential water-absorbing organ in terrestrial vertebrates to prevent desiccation. The class Chondrichthyes, comprised of sharks, rays, and skates, are isotonic to their marine environment, and thus do not require a functional colon. The Chondrichthyes are an excellent organism for developmental and physiological studies in evolutionary context because they have undergone little evolutionary change since their appearance 450 million years ago. Previous histochemical studies demonstrate potential water absorbing properties in the digestive tract of the little skate, Leucoraja erinacea (Theodosiou et al., 2007). To further examine the ability of the skate spiral intestine to absorb water, I examined the expression of the water-specific channel protein, aquaporin 4. Aquaporin 4 is expressed in the skate digestive tract with high levels in the epithelium of the distal spiral intestine. In addition, I measured water uptake across the membrane of the spiral intestine directly using physiology experiments. The distal spiral intestine absorbs water at a greater rate than the stomach and proximal intestine, and water uptake was not pressure dependent. Currently, we are examining the conservation of embryonic colon patterning genes by studying the role of Hoxd13 in developing chick and skate embryos. With this study, we hope to understand the origin of the colon in terrestrial vertebrates.

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