Date of Award

5-24-2012

Document Type

Thesis

Degree Name

Bachelor of Arts

First Advisor

Gillen, Chris

Abstract

The study of the scaling of metabolism provides an intriguing basis for the investigation into the structures and processes that drive energy exchange and growth. Isometric growth of a larval midgut predicts that the ratio of surface area to body mass decreases in larger larvae, providing the basis for a 0.67 metabolic scaling exponent. However, metabolic rate in Manduca sexta larvae scales with over a 0.90 exponent. We tested the hypothesis that compensation for decreasing midgut surface area occurs by an increase in density of apical enzymes and transporters per unit surface area of midgut. We measured mRNA abundance of five different midgut genes, the potassium amino acid coupled transporter KAAT1, the ion channel CAATCH1, a cation-chloride cotransporter masBSC, an aminopeptidase msAPN3 and a subunit of the vacuole-type H+ ATPase. Expression of KAAT1 was 2.3-3.1 fold higher in 5th instar compared to 4th instar and masBSC expressi on was 1.3-1.9 fold higher in 5th instar larvae. There was no change in expression of msAPN3, V-ATPase or CAATCH1 in the 5th relative to the 4th instar, although expression of msAPN3 and V-ATPase decreased over a three day interval in the 5th instar. We used RNA interference to study the physiological importance of KAAT1 midgut function. Droplet feeding of KAAT1 dsRNAs did not silence KAAT1 gene expression, but microinjections into the hemocoel produced mixed results, with the KAAT1 gene partially silenced in some trials and upregulated in others. The related CAATCH1 gene was knocked down with all injection trials.

Comments

Includes bibliographical references (p. 38-42)

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