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Juvenile hormones (JHs) are a group of acyclic sesquiterpenoids that regulate many aspects of insect physiology. JHs regulate development, reproduction, diapause, and polyphenisms.〔Riddiford, L. M. (1994) Adv. Insect Physiol. 24, 213–274.〕〔Wyatt, G. R. & Davey, K. G. (1996) Adv. Insect Physiol. 26, 1–155〕〔Nijhout, H. F. (1994) Insect Hormones (Princeton Univ. Press, Princeton)〕 In insects, JH (formerly called neotenin) refers to a group of hormones, which ensure growth of the larva, while preventing metamorphosis. Because of their rigid exoskeleton, insects grow in their development by successively shedding their exoskeleton (a process known as molting). Juvenile hormones are secreted by a pair of endocrine glands behind the brain called the corpora allata. JHs are also important for the production of eggs in female insects. JH was discovered in 1965 and the first of six molecular structures solved in 1967.〔Röller, H., Dahm, K.H., Sweeley, C.C., Trost, B.M., (1967). Angew. Chem. Internat. Edit. 6, 179-180〕 Most insect species contain only juvenile hormone (JH) III.〔Judy, K.J., Schooley, D.A., Dunham, L.L., Hall, M.S., Bergot, B.J., Siddall, J.B., 1973. ''Proc. Natl. Acad. Sci. U.S.A''. 70, 1509-1513〕 To date JH 0, JH I, and JH II have been identified only in the Lepidoptera (butterflies and moths). The form JHB3 (JH III bisepoxide) appears to be the most important JH in the Diptera, or flies.〔Richard D.S., Applebaum S.W., Sliter T.J., Baker F.C., Schooley D.A., Reuter C.C., Henrich V.C., Gilbert L.I. (1989) Juvenile Hormone Bisepoxide Biosynthesis in vitro by the Ring Gland of Drosophila melanogaster: A Putative Juvenile Hormone in the Higher Diptera. ''Proc Natl Acad Sci USA'' 86: 1421-1425〕 Certain species of crustaceans have been shown to produce and secrete methyl farnesoate, which is juvenile hormone III lacking the epoxide group.〔Laufer, H, Borst, D, Baker, FC, Carasco, C, Sinkus, M, Reuter, CC, Tsai, LW, and Schooley, DA. (1987) Identification of a juvenile hormone-like compound in a crustacean. Science 235: 202-205〕 Methyl farnesoate is believed to play a role similar to that of JH in crustaceans. Being a sesquiterpenoid, JH chemical structure differs significantly from the structure of other animal hormones. Some JH analogs have been found in conifers. ==Control of development== The primary control of juvenile hormone is by 1) the stimulation of the corpora allata by allatotropins〔Schooley, D.A., 1991. Identification of an allatostatin from the tobacco hornworm Manduca sexta Proc. Natl. Acad. Sci. USA 88, 9458-9462〕 short peptides which bind to G-protein coupled receptors〔Cusson, M., Prestwich, G.D., Stay, B., Tobe, S.S., 1991. Photoaffinity labeling of allatostatin receptor proteins in the corpora allata of the cockroach, Diploptera punctata. Biochem. Biophys. Res. Commun. 181, 736-742<〕> which signal the glands to produce JH, and 2, the inhibition of JH production by allatostatins. These fall into three classes, allatostatin A,〔Woodhead, A.P., Stay, B., Seidel, S.L., Khan, M.A., Tobe, S.S., 1989. Primary structure of four allatostatins: Neuropeptide inhibitors of juvenile hormone biosynthesis. Proc. Natl. Acad. Sci. USA 86, 5997-6001〕 allatostatin B,〔Reichwald, K., Unnithan, G.C., Davis, N.T., Agricola, H., Feyereisen, R., 1994 Expression of the allatostatin gene in endocrine cells of the cockroach midgut. Proc. Natl. Acad. Sci. USA 91, 11894-11898〕 and allatostatin C.〔Kramer, S.J., Toschi, A., Miller, C.A., Kataoka, H., Quistad, G.B., Li, J.P., Carney, R.L., Schooley, D.A., 1991. Identification of an allatostatin from the tobacco hornworm Manduca sexta. Proc. Natl. Acad. Sci. USA 88, 9458-9462〕 For a review of these control mechanisms see.〔Stay, B., Woodhead, A.P., 1993. Neuropeptide regulators of insect corpora allata. Am. Zool. 33, 357-364〕 Secondary control of the JH titre found in the haemolymph of the developing insect is metabolic inactivation of JH by JH-specific esterase and juvenile hormone epoxide hydrolase.〔White, A.F., 1972. Metabolism of the Juvenile Hormone Analogue Methyl Farnesoate 10,11-Epoxide in Two Insect Species. Life Sci. 11, 201-210〕 During ecdysis the form of the old cuticle laid down before the next moult is controlled by the JH level in the insect. JH maintains a juvenile state. The level gradually decreases during the development of the insect, allowing it to proceed to successive instars with each molt. This has been demonstrated in various studies, most prominently that by V. B. Wigglesworth in 1960s. In this study, two adult ''Rhodnius'' had their blood systems linked, ensuring that the JH titre in both would be equal. One was a third instar ''Rhodnius'', the other was a fourth instar. When the corpora allata of the third instar insect were removed, the level of JH was equal in both insects to that in the fourth instar animal, and hence both proceeded to the fifth instar at the next moult. When the fourth instar ''Rhodnius'' had its corpora allata removed, both contained a third instar level of JH and hence one proceeded to instar four, and the other remained at this instar. Generally, the removal of the corpora allata from juveniles will result in a diminutive adult at the next moult. Implantation of corpora allata into last larval instars will boost JH levels and hence produce a supernumary (extra) juvenile instar etc. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Juvenile hormone」の詳細全文を読む スポンサード リンク
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