The mevalonate pathway in insects has two important peculiarities, the absence of the sterol branch and the synthesis of juvenile hormone (JH), that may have influenced the mechanisms of regulation. The data available on these mechanisms indicate that cholesterol does not play a regulatory role and that JH modulates transcript levels of a number of genes of the mevalonate pathway or can influence the translatability and/or stability of the transcripts themselves. These data suggest that the mevalonate pathway in insects can best be interpreted in terms of coordinated regulation, in which regulators act in parallel to a number of enzymes, as occurs in the cholesterol-driven pathway in vertebrates.

https://www.researchgate.net/profile/Md_Piulachs/publication/8359243_The_mevalonate_pathway_and_the_synthesis_of_juvenile_hormone_in_insects/links/02bfe50c9a2a4ef90c000000.pdf

The mevalonate pathway and the synthesis of juvenile hormone in insects.

Evidence for a new juvenile hormone in a stink bug, Plautia stali

The great diversity seen in the cyclorrhaphous dipterans suggests that it is unlikely that juvenile hormone (JH) plays a common role within the group. The role that JH does play appears to be determined by adult lifestyle and nutritional impact on the neuroendocrine system. Using Phormia regina as a model system, the importance of JH in the reproductive biology of other cyclorrhaphous dipterans are compared. The different JHs found within this group, and the species studied, are presented. The effects of JH on the disappearance of pupal fat body in adults, accessory reproductive gland development, and the ontogeny of sexual behavior are discussed. As for oogenesis, vitellogenin biosynthesis and its uptake are described in more detail. Arch. Insect Biochem. Physiol. 35:513–537, 1997. © 1997 Wiley-Liss, Inc.

Juvenile hormone regulation of reproduction in the cyclorrhaphous diptera with emphasis on oogenesis

The metabolism of [U-14C]isoleucine was examined in different tissues of five species of lepidopteran and four species of non-lepidopteran insects. Slices of fat body, epidermis, Malpighian tubule, gut, and muscle were incubated in a culture medium containing [U-14C]isoleucine; the medium was analyzed by ion-exclusion LC to quantify labeled metabolites. Tissues of lepidopteran insects secrete high levels of metabolites including 2-keto-4-methylvalerate, 2-methylbutyrate, propionate, and acetate. Tissues of non-lepidopteran insects secrete low amounts of these acids. Analysis of isoleucine transaminase activity in selected tissues of non-lepidopteran insects indicated that those tested contain significant activity. These results demonstrate that tissues of lepidopteran insects have a unique ability to secrete short chain acids, derived from isoleucine, into the medium. The secretion of propionate correlates with the ability to synthesize ethyl-branched juvenile hormones and indicates the presence of an efficient transport system for short chain acids. We also monitored the secretion of acidic metabolites of isoleucine by different tissues of the rat. Muscle was most active in secreting keto acid whereas heart secreted high levels of 2-methylbutyrate. Negligible quantities of metabolites of isoleucine were secreted by the liver.

A comparative catabolism study of isoleucine by insect and mammalian tissues

Juvenile hormone synthesis by ring glands of the blowfly Lucilia cuprina

The qualitative juvenile hormone (JH) profile in lepidopteran species, as determined by both in vivo and in vitro techniques, is markedly different from that in insects from other orders, the majority of which contain only JH III. A gas chromatographic-mass spectrometric (GC-MS) method for quantification of JHs in vivo was adapted to study the mode of JH biosynthesis by corpora allata incubated in vitro with selected 14C-radiolabeled substrates of high specific activity. We analyzed derivatives of JH using selected ion monitoring to measure ratios of the fragment ion and corresponding ions 2,4, and 6 mass units higher, allowing determination of dilution of the propionate unit which is incorporated as an intermediate. The results showed conclusively that the ethyl branch of JH II from Manduca sexta derives ultimately from metabolism of the branched-chain amino acids isoleucine and valine. A purification procedure for isolation of JHs from biological tissue was modified to allow isolation of JH acids and compounds structurally related to JH, including JH diols, methyl farnesoate (MF), farnesoic acid (FA), and farnesol. To allow analysis, JH acids were methylated and the resulting JHs were detected and quantified, as their d3-methoxyhydrin derivatives, by GC-MS with selected ion monitoring (SIM). A detailed study of fifth stadium Manduca sexta showed that JH I and II acids predominate over the corresponding esters at the prepupal stage. GC-MS methods were devised for quantification of JH diols, MF, FA, and farnesol from arthropods. None of the latter compounds, nor any of the known JHs, could be detected in the hemipteran Oncopeltus fasciatus. Ring glands from a few dipteran species appear to secrete a new JH in vitro, and details are given for the isolation and analysis of this compound. Haemolymph from several crustaceans contain detectable levels of MF, and mandibular organs from crustaceans secrete MF and/or FA in vitro.

Use of Microderivatization Techniques in Combination with Thin-Layer Chromatography, Liquid Chromatography and Gas Chromatography-Mass Spectrometry for Investigation of Juvenile Hormones and Related Compounds

L. W. Tsai

Papers

Use of Microderivatization Techniques in Combination with Thin-Layer Chromatography, Liquid Chromatography and Gas Chromatography-Mass Spectrometry for Investigation of Juvenile Hormones and Related Compounds