Permeability and disruption of the peritrophic matrix and caecal membrane from Aedes aegypti and Anopheles gambiae mosquito larvae

In mosquito larvae, the peritrophic matrix (PM) separates the gut contents from the intestinal epithelium. This report describes a new in vivo assay for estimating PM permeability. The assay also allows for assessment of the permeability of the caecal membrane, a structure that separates each caecum from the gut lumen. Permeability was estimated by the appearance of fluorescently-labeled dextrans (size range 4,400 to 2 million Da) within the gastric caecae of mosquito larvae. While the intact peritrophic matrix was impermeable to 2 million Da dextran particles, it was permeable to dextran particles of 148 kDa and smaller. The caecal membrane appears to have considerably smaller pores, being permeable only to dextrans of 19.5 kDa and smaller. The assay was also used to devise a treatment that disrupts the PM sufficiently to allow the passage of virus-sized particles. Dithiothreitol and to a lesser extent, chitinase were effective in disrupting the PM. Cycloheximide had a small effect; Polyoxin D, Pronase and calcofluor did not alter the permeability to 2 million Da dextran particles. Disruption of the PM is discussed in the context of infecting mosquitoes with retroviral transformation vectors.