PEPTIDES IN THE LOCUSTS, LOCUSTA-MIGRATORIA AND SCHISTOCERCA-GREGARIA

The first peptide identified in locusts was adipokinetic hormone I(AKH -I), a neurohormone mobilizing lipids from the fat body. No other locu st peptides were isolated until 1985. From then on peptide identificat ion started to boom at such a tremendously fast rate that even special ists in the field could hardly keep track. At this moment the total nu mber of different insect neuropeptide sequences exceeds 100. Currently , the locusts Locusta migratoria and Schistocerca gregaria are the spe cies from which the largest number of neuropeptides has been isolated and sequenced, namely 56. Myotropic bioassays have played a major role in the isolation and subsequent structural characterization of locust neuropeptides. They have been responsible for the discovery of locust amyotropins [4], locustapyrokinins [2], locustatachykinins [5], locust akinin [1], locusta accessory gland myotropins [2], locustasulfakinin [1], cardioactive peptide [1], and locustamyoinhibiting peptides [4]. Members of the myotropin peptide families have been associated with a variety of physiological activities such as myotropic activities, pher omonotropic activities, diapause induction, stimulation of cuticular m elanization, diuresis, pupariation, and allatostatic activities. Recen tly, we have identified in Schistocerca 10 peptides belonging to the a llatostatin peptide family, which inhibit peristaltic movements of the oviduct. Some of the myotropins appear to be important neurotransmitt ers or modulators innervating the locust oviduct, the salivary glands, the male accessory glands, and the heart, whereas others are stored i n neurohemal organs until release in the hemolymph. Some myotropic pep tides have been found to be releasing factors of neurohormones from th e corpora cardiaca. Several peptides isolated in locusts appear to be unique to insects or arthropods; others seem to be members of peptide families spanning across phyla: two vasopressin-like peptides, FMRFami de-related peptides, Locusta diuretic hormone (CRF-like), Locusta insu lin-related peptide, locustatachykinins, locustasulfakinin (gastrin/CC K-like). In a systematic structural study of neuropeptides in Locusta, several novel peptides have been isolated from the corpora cardiaca a nd the pars intercerebralis. They include the neuroparsins, two 6-kDa dimeric peptides, and three proteinase inhibitors. Ovary maturating pa rsin is the first gonadotropin identified in insects. The isolation of a peptide from an ovary extract that inhibits ovary maturation in Sch istocerca gregaria is currently underway in our lab. The proteinase in hibitors, recently found to be mainly transcribed in the fat body, are believed to play a role in defense reactions of insects. Finally, a l ocust ion transport peptide and a peptide stimulating salivation recen tly identified can be added to this extensive list of locust peptides. (C) 1997 Elsevier Science Inc.