Date of Award
Bachelor of Arts
Surface area to volume ratio decreases as animals grow, resulting in a decrease in relative epithelial surface area for gas exchange and nutrient uptake. Larger animals may compensate by increasing surface area with in-folding, increasing the density of transport proteins, or decreasing mass-specific metabolic rate. Manduca sexta grow 10,000-fold over an 18 day period, molting through five stages, or instars. Animals grow bigger by increasing cell size during intermolt, while cell number increases by cell division during molting. We investigated whether development has an effect on the expression of genes encoding metabolic enzymes and structural proteins. RT-PCR was used to measure the relative expression of select genes involved in glycolysis, the pentose phosphate pathway (PPP), and the cytoskeleton in 4th and 5th instar larvae. While there were few changes in gene expression between instars, expression within 5th instar was variable. Over the course of the 5th instar, expression decreased between 9.3 and 86.2 fold in the anterior midgut for 5 out of the 7 genes. Whereas in the posterior midgut expression increased between 1.5 and 14.9 fold over the course of the 5th instar. Expression was 3.3 to 108.8 fold lower in the posterior region of the midgut relative to the anterior midgut at the beginning of 4th and 5th instar. The variability in 18s rRNA, a commonly used endogenous control, calls into question its use as an internal standard. Further work needs to be done to determine if observed patterns of gene expression are related to insect development or metabolic scaling.
Wahl, Kelly, "Relative expression of select genes in the Manduca sexta midgut" (2012). Honors Theses. 84.