Allatostatins

Definition
Allatostatins (ASTs) are pleiotropic neuropeptide hormones in insects and crustacean. There major function in the insect is the inhibition of juvenile hormone synthesis by the corpora allata and reduce their food intake1.

Discovery
The first identified ASTs were isolated from brain-retro cerebral complexes of the cockroach Diploptera punctata2.

Classification
ASTs encompass a group of three families determined by consensus sequences, the cockroach type representing the FGLa family, the cricket type representing the W(X)6 Wa family and the PISCF family1.

Structural Characteristics
AST’s are 8-13 amino acids long, are amidated, and show sequence similarity, including a 3-amino acid sequence at the C-terminal end that is common to all four peptides. The peptide sequences are as follows: allatostatin-1, Ala-Pro-Ser-Gly-Ala-Gln-Arg-Leu-Tyr-Gly-Phe-Gly-Leu-NH2; allatostatin-2, Gly-Asp-Gly-Arg-Leu-Tyr-Ala-Phe-Gly-Leu-NH2; allatostatin-3, Gly-Gly-Ser-Leu-Tyr-Ser-Phe-Gly-Leu-NH2; and allatostatin-4, Asp-Arg-Leu-Tyr-Ser-Phe-Gly-Leu-NH23.

Mode of action
In mammalian cells, allatostatin bind to AST receptors to open G-protein coupled inward rectifying potassium channels, resulting in reduced membrane potential and input resistance4.

Function
The action of ASTs have been largely defined in individual species, in the case of the FGLamide family, such actions include (1) the inhibition of vitellogenin production by fat body in cockroaches, (2) the inhibition of myotropic activity, particularly in gut tissue of Dictyoptera and Orthoptera, (3) regulation of release of digestive enzymes in the midgut of cockroaches, (4) neurotransmission in crab stomatogastric ganglion and possibly cockroach CNS.The biological action of the W(x) 6 Wamide family include (1) Inhibition of ectysteroid biosynthesis (prothoracicostatic activity) by prothoracic glands in silk moth and ovaries of crickets, (2) Inhibition of locust oviduct muscle, (3) Inhibition of spontaneous muscle contraction in foregut of the cockroach. The PISCF family display biological effect similar to the two AST families inhibiting contraction in larval drosophila heart muscle. This peptide family plays a role in the regulation of migratory flight in Lepidoptera.

References
1.Stay B and Tobe SS (2007). "The role of allatostatins in juvenile hormone synthesis in insects and crustaceans". Annu. Rev. Entomo., 52: 277–99.
2.Pratt GE, Farnsworth DE, Fok KF, Siegel NR, McCormack AL, Shabanowitz J, Hunt DF, Feyereisen R (1991). Identity of a second type of allatostatin from cockroach brains: an octadecapeptide amide with a tyrosine-rich address sequence. Proc Natl Acad Sci., 88(6): 2412–2416.
3.Woodhead AP, Stay B, Seidel SL, Khan MA, Tobe SS (1989). Primary structure of four allatostatins: neuropeptide inhibitors of juvenile hormone synthesis. Proc Natl Acad Sci., 86(15):5997-6001.
4.Tan EM, Yamaguchi Y, Horwitz GD, Gosgnach S, Lein ES, Goulding M, Albright TD, Callaway EM (2006). Selective and quickly reversible inactivation of mammalian neurons in vivo uses the Drosophila allatostatin receptor. Neuron, 1:57–170.