Allatostatins: Diversity in structures, functions, and occurrence

M.W. Lorenz

Department of Animal Ecology 1, University of Bayreuth, 95440 Bayreuth, Germany

Allatostatins (ASTs) are neuropeptides that inhibit juvenile hormone biosynthesis by insect corpora allata. To date, they can be divided into three families: the first ASTs have been identified from the brain of the cockroach Diploptera punctata. These peptides belong to the so-called cockroach- or Phe-Gly-Leu-AST family. Peptides of this family have been subsequently isolated from other cockroaches as well as from stick insects, locusts, crickets, blowflies, mosquitoes, honey bees, moths, and even from a crustacean. Their allatostatic activity, however, seems to be restricted to cockroaches and crickets. A second “family“ of ASTs is represented by a single peptide, the Mas-AST, isolated from the tobacco hornworm Manduca sexta. This peptide shows allatostatic activity only in lepidopterans. A third family of ASTs has been isolated from the cricket Gryllus bimaculatus and from the stick insect Carausius morosus. These peptides belong to the so-called W 2 W 9 amide family, previously isolated from the locust Locusta migratoria and from M. sexta, where they inhibit contractions of smooth muscles. Their allatostatic function seems to be restricted to crickets. Immunohistochemical studies in insects and also in non-insect invertebrates like Hydrozoa, Cestoda, Trematoda, Turbellaria, Nematoda, Oligochaeta, Gastropoda, Cephalopoda, and Crustacea, where Phe-Gly-Leu-AST immunoreactivity has been found not only in the central but also in the stomatogastric nervous system, points towards additional (basic?) functions of these peptides as neurotransmitters/neuromodulators with roles in locomotion, feeding, reproduction, and sensory perception. This assumption is corroborated by several findings on AST action in insects: for both the Phe-Gly-Leu and the W 2 W 9 amide family a myoinhibiting role has been established. In addition, the Phe-Gly-Leu-AST inhibit vitellogenin release from the periovaric fat body of the cockroach Blattella germanica, whereas the W 2 W 9 amide peptides are potent inhibitors of ovarian ecdysteroid biosynthesis in G. bimaculatus. Since all these physiological actions directly or indirectly affect developmental and reproductive events, ASTs play a crucial role in insects. On the basis of recent results on allatostatic peptides in crickets and stick insects, the role and function of these multifunctional peptides in insect reproduction and development, the use of ASTs (and analogues thereof) in insect pest control, and possible evolutionary relationships will be discussed. Index terms: Ensifera, Phasmatodea, Neuropeptides, Juvenile Hormone, Ecdysone

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