Digestive enzyme compartmentalization and recycling and sites of absorption and secretion along the midgut of Dermestes maculatus (Coleoptera) larvae

Abstract

Bostrichiformia is the less known major series of Coleoptera regarding digestive physiology. The midgut of Dermestes maculatus has a cylindrical ventriculus with anterior caeca. There is no cell differentiation along the ventriculus, except for the predominance of cells undergoing apocrine secretion in the anterior region. Apocrine secretion affects a larger extension and a greater number of cells in caeca than in ventriculus. Ventricular cells putatively secrete digestive enzymes, whereas caecal cells are supposed to secrete peritrophic gel (PG) glycoproteins. Feeding larvae with dyes showed that caeca are water-absorbing, whereas the posterior ventriculus is water-secreting. Midgut dissection revealed a PG and a peritrophic membrane (PM) covering the contents in anterior and posterior ventriculus, respectively. This was confirmed by in situ chitin detection with FITC-WGA conjugates. Ion-exchange chromatography of midgut homogenates, associated with enzymatic assays with natural and synthetic substrates and specific inhibitors, showed that trypsin and chymotrypsin are the major proteinases, cysteine proteinase is absent, and aspartic proteinase probably is negligible. Amylase and trypsin occur in contents and decrease along the ventriculus; the contrary is true for cell-membrane-bound aminopeptidase. Maltase is cell-membrane-bound and predominates in anterior and middle midgut. Digestive enzyme activities in hindgut are negligible. This, together with dye data, indicates that enzymes are recovered from inside PM by a posterior-anterior flux of fluid outside PM before being excreted. The combined results suggest that protein digestion starts in anterior midgut and ends in the surface of posterior midgut cells. All glycogen digestion takes place in anterior midgut.

Pyrosequencing of the midgut transcriptome of the poplar leaf beetle Chrysomela tremulae reveals new gene families in Coleoptera

“…The peritrophic membrane (PM) separates the food bolus in the insect midgut, in this case poplar leaves, from the midgut epithelium and associated brush border membrane. This membrane is composed of chitin and proteins and forms a permeable barrier that protects the midgut epithelium from erosion by the food bolus whilst allowing for the passage of enzymes and solutes involved in extracellular digestion in the gut (Caldeira et al, 2007). The PM requires continuous repair and replacement and it is therefore interesting to note dominance of enzymes involved in the binding (peritrophins, seven contigs), breakdown (chitinases, 36 contigs) and remodeling (chitin synthase, seven contigs, and chitin deacetylase, 13 contigs) of chitin ( Table 3), suggesting that maintenance and remodeling of chitin in the PM occupies a major part of the C. tremulae transcriptional midgut machinery.…”

A gut-specific chitinase gene essential for regulation of chitin content of peritrophic matrix and growth of Ostrinia nubilalis larvae

“…Several mechanisms have been proposed by which digestive enzymes secreted from midgut epithelium penetrate the PM to reach the food bolus (Santos and Terra, 1986;Barbehenn and Martin, 1995;Ferreira et al, 1999;Edwards and Jacobs-Lorena, 2000;Colditz et al, 2002;Villalon et al, 2003;Caldeira et al, 2007;Oviedo et al, 2008). A few studies have suggested a role for gut chitinases in controlling the porosity of chitin-containing PM (Shen and Jacobs-Lorena, 1997).…”

Amylase gene expression patterns in Helicoverpa armigera upon feeding on a range of host plants

“…Mucilaginous components of okra probably have a longer retention time in the gut regions and affects expression of digestive enzymes. Major hydrolases are distributed in the anterior midgut, middle midgut, posterior midgut and hindgut of Dermestus maculatus (Coleoptera) larvae (Caldiera et al, 2007). Furthermore, differences in amylase expression levels in oral secretions of the second, fourth and sixth instars feeding on marigold and maize indicate larval-stage specificity.…”