Effect of Body Size on Expression of Manduca sexta Midgut Genes

Abstract

Isometric growth of larval insect midgut predicts that the ratio of midgut surface area to body mass decreases as larvae grow. Gut tissue and gut content masses were measured in first through fifth instar Manduca sexta larvae. Wet mass of gut tissue increased in relationship to body mass with a scaling exponent of 0.85 compared to an exponent of 1.33 for gut content mass, suggesting that surface area becomes increasingly limiting in larger larvae. To test the hypothesis that compensation for the decrease in relative surface area of the midgut occurs by increased expression of membrane proteins, we compared midgut mRNA expression in fourth and fifth instar. Surveyed genes encoded apical membrane proteins with diverse functions, including the potassium amino acid transporter KAAT1, ion channel CAATCH1, aminopeptidase msAPN3, V-type H-ATPase E subunit, and cation chloride cotransporter masBSC. KAAT1 was expressed 300- to 1500-fold higher in middle and posterior midgut compared to anterior midgut. Expression of msAPN3 was approximately 200-fold higher in posterior midgut than middle midgut. Expression of KAAT1 was 2.3- to 3.1-fold higher in fifth compared to fourth-instar larvae, and masBSC expression was 1.3- to 1.9-fold higher in fifth-instar larvae. Expression of msAPN3 and V-ATPase, but not KAAT1, decreased as body mass increased within the fifth instar. Although the increased expression of KAAT1 and masBSC in fifth-instar larvae supports the hypothesis of increased membrane protein expression in larger larvae, results from the other genes do not support this hypothesis.

Metabolic Scaling in Complex Living Systems

“…Since IGF-1 has important effects on growth and metabolism [163,421], it is possible that this regulatory factor plays a significant role in metabolic scaling. Studies of how the expression of genes involved in controlling resource uptake and use scale with body size could also provide useful insights (e.g., see [422][423][424]). Elucidation of the regulatory controls of metabolic scaling promises to be an exciting area for future research.…”

Testing mechanistic models of growth in insects

“…The proposed increasing specific assimilation implies that these organs do not grow isomorphically. Interestingly, it has been found in the lepidopterans Bombyx mori [19] and Manduca sexta [20], that the midgut mass increases faster than predicted by isomorphic scaling. Indeed, it is well known that insects have significant physiological plasticity in organ size and can increase gut size to deal with nutrient stress [21,22].…”

The Synergistic Impact of Honey and Lemon Juice-Enriched Mulberry Diets on the Silk Gland Metabolism and Energetics of Larval Silkworm, Bombyx mori

“…The glucose derived from dietary and metabolic sources, is the chief source of energy for silk production [11] . When the glucose is in short supply, the silk gland traps the energy from glucogenic amino acids [83,84] . In silk gland, the glucose is routed through two channels depending on the availability/non-availability of succinic dehydrogenase (SDH) activity.…”