Little is known about the composition and function of the mosquito peritrophic matrix (PM), a physical barrier that pathogens must traverse to complete their life cycles. Anopheles gambiae and Aedes aegypti PM proteins induced by blood or by a protein-free meal have been characterized by the use of 2-D gel electrophoresis and lectin-binding affinity assays. More than forty proteins have been identified in both species. Over half of the PM proteins of both mosquitoes migrate identically. Many PM proteins appear to be glycosylated, primarily by high mannose N-linked glycosyl groups.
A gut-specific carboxypeptidase A gene (AeCPA) from the mosquito, Aedes aegypti, was cloned and characterized. The gene has an open reading frame that predicts a protein of 427 amino acids, 61% of which are identical to an Anopheles gambiae carboxypeptidase A sequence. AeCPA messenger RNA (mRNA) was not detected during larval and pupal development. In situ hybridization experiments indicated that AeCPA mRNA is expressed by posterior midgut epithelial cells. In sharp contrast to An. gambiae carboxypeptidase A gene expression, AeCPA mRNA accumulates to high levels only late ( approximately 16-24 h) after ingestion of a blood meal. The temporal profile of AeCPA gene induction is similar to that of Ae. aegypti late trypsin, suggesting the existence of common regulatory elements.
Carboxypeptidase B (CPB) activity was detected in the guts of strain G-3 of Anopheles gambiae (Giles) and Aedes aegypti (L.). Mosquitoes were examined 3-5 d after emergence following exposure to 20% sucrose, from 0 to 4 h after feeding on a meal of latex beads in saline, and from 0 to 96 h after blood feeding. CPB activity was assayed in whole-gut homogenates, including lumenal contents and peritrophic matrix, by following the hydrolysis of a substrate specific for CPB-[3H]-benzoyl-L-Phe-L-Arg. Homogenates were divided into cytosolic plus lumenal components and membrane-associated components. Activity levels changed in response to feeding, decreasing in response to distention by saline plus latex and increasing only in response to blood. Overall, CPB activity was higher in unfed An. gambiae than in unfed Ae. aegypti. Detection of CPB activity in the peritrophic matrix of both species indicated that this enzyme was secreted actively into the gut lumen. In An. gambiae, CPB activity was optimal at pH 8, and thiol-type CPB was the predominant form detected. The data indicated that CPB in An. gambiae was regulated by both physical and chemical factors.
The effects of variation in diet temperature, mouthpart deployment and the addition of bicarbonate to a saline-ATP diet were investigated for their effects on amount ingested and diet destination in female Aedes aegypti (L.). Mouthpart deployment was achieved by having the insects feed through a membrane, or from a free-liquid surface with mouthparts intact, or with the fascicle separated from the labial groove.Under the 'feeding through membrane' protocol, a 6-fold increase in the percentage of Aedes feeding on ATP-diets was recorded at 37°C compared with 21°C. Bicarbonate (9.5 or 1 9 m~) induced a 3-fold increase in numbers feeding at both 21°C and 37°C. Neither diet temperature nor bicarbonate content appeared to affect meal size. The pH of all diets was adjusted to 7.0. Diet was directed primarily to the midgut for all diets tested under this regimen, with the exception of the saline-ATP-19 mM NaHC03 at 37°C which caused the diet to be directed primarily to the crop.Under the 'feeding without membrane through feeding tube' protocol, females showed little control over diet destination. Female Aedes aegypti exhibited no strong response to ATP when the mouthparts were immersed in 21°C diets in feeding tubes and few of these insects ingested large meals. The addition of bicarbonate to the ATP diets did not enhance feeding under these test conditions.
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