IDENTIFICATION OF NEUROPEPTIDES IN THE MIDGUT OF PARASITIZED INSECTS - FLRFAMIDES AS CANDIDATE PARACRINES

Parasitism of Manduca sexta (Lepidoptera: Sphingidae) larvae by the br aconid wasp Cotesia congregata (Hymenoptera: Braconidae) leads to accu mulation of peptides in host neurons and neurosecretory cells of the c entral nervous system (CNS) and neurons and endocrine/paracrine cells of the midgut. This accumulation has now facilitated the characterizat ion of two new members of the FLRFamide family from midguts of parasit ized larvae. The peptides, given the names F24 and F39, are 24 and 39 amino acids in length with the sequences VRDYPQLLDSGMKRQDVVHSFLRFamide and YAEAAGEQVPEYQALVRDYPQLLDSGMKRQDVVHSFLRFamide. The sequence of F24 is identical to the C-terminal 24 amino acids of F39. The C-terminal 10-mer of each is identical to a previously characterized decapeptide neurohormone (F10). This sequence is preceded by a potential processin g site. In nonparasitized insects F39 was present at several-fold the amount of F24. In parasitized insects F24 and F39 accumulate in the mi ddle and posterior regions of the midgut, which are enriched in endocr ine/paracrine cells reacting with FLRFamide antisera. In the combined brain and subesophageal ganglion F39 was not detected and the amount o f F24 never exceeded 2 fmol per Br/SEG. Of the three peptides, only F1 0 was found in the hemolymph. Thus, F24 and F39 may be intermediates i n the biosynthesis of F10 and may themselves be released locally from endocrine/paracrine cells in the midgut epithelium. (C) 1997 Elsevier Science Ireland Ltd.