Neuropeptides in locusts: Progress in the search for functions

L. Schoofs 1, M. Breuer 1, A. Cerstiaens 1, G. Baggerman 1, Z. Wei 1, E. Clynen 1, T. Vercammen 1, S. Tanaka 2 & A. De Loof 1

1 Zoological Inst., K.U.Leuven, Naamsestr. 59, 3000 Leuven, Belgium, 2 NISES, Tsukuba, Ibaraki 305-8634, Japan

Immunohistochemical results on FMRFamide-related peptides (FaRPs) have been reported extensively in arthropods, suggesting many possible roles for these peptides associated with behavioural and physiological events, including reproduction. Our recent study provides a clear effect for the neuropeptide F (NPF) members of this family. NPF-related peptides act as gonadostimulins in Locusta migratoria. Consecutive injections 0.05 µg of peptide into 6-day old virgin females were able to accelerate egg development significantly. In vertebrates, the peptides cholecystokinin (CCK), neuropeptide Y (NPY), galanin, bombesin and orexin are known to be involved in the control of food intake. The locust neuropeptide, locustasulfakinin, as well as other naturally occurring insect sulfakinins, which display substantial sequence similarities with the vertebrate gastrin/CCK peptide family, significantly inhibit food uptake in fifth instar nymphs of the locust, Schistocerca gregaria in a dose-dependent manner within a fixed 20 min time period. The induced satiety effect ranged from 13% inhibition (10 pmol of injected peptide) to over 50% inhibition at 1 nmol. Analogous to CCK in vertebrates, the sulfate group is required for activity. In response to crowding, locusts develop characteristic black patterns that are well discernible in the gregarious phase at outbreaks. Using a bioassay with an albino mutant of L. migratoria, the responsible dark colour inducing hormone was isolated corpora cardiaca (CC) extracts and identified as [His 7 ]-corazonin. In isolated (solitary) nymphs of L. migratoria, [His 7 ]-corazonin induces gregarious black patterns. By differential peptide profiling of isolated versus gregarious locust nervous tissue and haemolymph extracts, we now aim at the identification of phase-specific neuropeptides. We conclude that neuropeptides previously identified on the basis of their myotropic activity appear to be regulatory hormones of physiological processes. In order to exert their effect, these peptides have to be released in the haemolymph. Currently, haemolymph titres of the regulatory hormones are being established. In addition, we are studying the release of neuropeptides from the CC using mass spectrometry methodology. We recently found that in addition to the AKHs, serine protease inhibitors are released into a medium with high potassium concentration. Another small peptide encoded in the B-chains of the AKH precursor was likewise identified in the secretion mixture of peptides from the corpora cardiaca. The application of mass spectrometry in the study of peptide-releasing factors will be discussed.

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