Chitin is only a minor component of the peritrophic matrix from larvae of Lucilia cuprina

The gut of most insects is lined with a peritrophic matrix that facilitates the digestive process and protects insects from invasion by micro-organism s and parasites. It is widely accepted that the matrix is composed of chiti n, proteins and proteoglycans. Here we critically re-examine the chitin con tent of the typical type 2 peritrophic matrix from the larvae of the fly Lu cilia cuprina using a range of techniques. Many of the histochemical and bi ochemical techniques indicate the presence of chitin, although they are oft en adversely influenced by the presence of highly glycosylated proteins, a principal component of the matrix. The alkali-stable fraction, which is use d as an indicator of the maximum chitin content in a biological sample, is only 7.2% of the weight of the matrix. Larvae fed on the potent chitin synt hase inhibitor polyoxin D or the chitin-binding agent Calcofluor White, sho wed strong concentration-dependent inhibition of larval weight and survival but no discernible effects on the matrix structure. A bacterial endochitin ase fed to larvae had no effect on larval growth and no observable effect i n vitro on the structure of isolated peritrophic matrix. RT-PCR did not det ect a chitin synthase mRNA in cardia, the tissue from which PM originates. It is concluded that chitin is a minor structural component of the type 2 p eritrophic matrix of this insect. (C) 2000 Elsevier Science Ltd. All rights reserved.