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.

Developments during the past 20 years are reviewed for four aspects of crustacean growth. These are the hormonal control of moulting, the effects of external factors on growth rate, the patterns of growth and the determination of age. Hormonal control. The nature and structure of Moult Inhibiting Hormone has been determined, though the mechanism by which it inhibits crustecdysone production is still unclear. A role in moult control by Crustacean Hyperglycaemic Hormone has been demonstrated, but needs clarification. Methyl farnesoate, a juvenile hormone like substance, occurs in Crustacea: however, a clear function as a juvenile hormone has yet to be shown. External factors. The effect of increased temperature in reducing moult increments is supported by further data. Reduced food supply causes smaller moult increments and longer intermoult periods: the latter effect is generally proportionately greater. A role for CHH in this process is hypothesised. Patterns of growth. Little advance has occurred in understanding the rationale for the diversity of growth patterns. Computer modelling offers promise, but is constrained by lack of data on natural mortality for validation. Determination of age. The basic methods available remain size frequency analysis and tagging programmes. There have been advances in technology and methods of analysis, but no major breakthrough. Novel methods include radionuclide ratios (expensive, complex and give only duration of current intermoult), lipofuschin pigment assay (promising, but needs further validation), and annular structures in the infra-cerebral organ (still very speculative).

Growth in Crustacea — twenty years on

Control of reproductive development in crustaceans requires neuropeptides, ecdysone and methyl farnesoate (MF). A major source of neuropeptides is the X-organ–sinus gland (XO–SG) complex located in the eyestalk ganglia of crustaceans. The other regulatory factors (either peptides or neuromodulators) are produced in the brain and thoracic ganglia (TG). Two other regulatory non-peptide compounds, the steroid ecdysone and the sesquiterpene MF, are produced by the Y-organs and the mandibular organs, respectively. In the current review, I have tried to recapitulate recent studies on the role of gonadal regulatory factors in regulating crustacean reproduction.

* AG
 : androgenic gland
 AGH
 : androgenic gland hormone
 cAMP
 : cyclic adenosine monophosphate
 CHH
 : crustacean hyperglycemic hormone
 DA
 : dopamine
 dsRNAi
 : double-stranded RNA interference
 EPA
 : eicosapentaenoic acid
 ESA
 : eyestalk ablation
 FA
 : farnesoic acid
 FA-O-MeT
 : farnesoic acid O -methyl transferase
 FSH
 : follicle stimulating hormone
 GIH
 : gonad inhibitory hormone
 GSF
 : gonad stimulating factor
 HCG
 : human chorionic gonadotrophin
 HP
 : hepatopancreas
 HPLC
 : high performance liquid chromatography
 5-HT
 : 5-hydoxytryptamine
 JH
 : juvenile hormone
 LH
 : luteinizing hormone
 MeVg1
 : Metapenaeus ensis Vg1
 MF
 : methyl farnesoate
 MIH
 : molt inhibiting hormone
 MO
 : mandibular organ
 MS
 : mass spectroscopy
 OA
 : octopamine
 PG
 : prostaglandin
 SG
 : sinus gland
 SP
 : spiperone
 TG
 : thoracic ganglia
 Vg
 : vitellogenin
 VIH
 : vitellogenesis inhibiting hormone

/pdf/reproductive-regulators-in-decapod-crustaceans-an-overview-moonqcbgho.pdf

Reproductive regulators in decapod crustaceans: an overview.

The CHH-superfamily of multifunctional peptide hormones controlling crustacean metabolism, osmoregulation, moulting, and reproduction

The main endocrine-regulated processes of crustaceans have been reviewed in relation to the effects of endocrine-disrupting compounds (EDCs). Molting has been shown to be inhibited by several organic pollutants, such as xenoestrogens and related compounds, as well as by some pesticides. Most of these disrupters are thought to interfere with ecdysone at target tissues, although only for a few has this action been demonstrated in vitro. The heavy metal cadmium appears to inhibit some ecdysone secretion. Juvenoid compounds have also been shown to inhibit molting, likely by interfering with the stimulatory effect of methyl farnesoate. A molt-promoting effect of emamectin benzoate, a pesticide, has also been reported. As for reproduction, a variety of organic compounds, including xenoestrogens, juvenoids and ecdysteroids, has produced abnormal development of male and female secondary sexual characters, as well as alteration of the sex ratio. Cadmium and copper have been shown to interfere with hormones that stimulate reproduction, such as methyl farnesoate, as well as with secretion of the gonad inhibiting hormone, therefore affecting, for example, ovarian growth. Several heavy metals were able to produce hyperglycemia in crustaceans during short times of exposure; while a hypoglycemic response was noted after longer exposures, due to inhibition of secretion of the crustacean hyperglycemic hormone. The ecological relevance of EDCs on crustaceans is discussed, mainly in relation to the identification of useful biomarkers and sentinel species. New experimental approaches are also proposed.

/pdf/endocrine-disruption-in-crustaceans-due-to-pollutants-a-r7dytvcrpp.pdf

Endocrine disruption in crustaceans due to pollutants: a review.

Juvenile hormone (JH) has central roles in the regulation of insect development and reproduction but has not previously been identified in other arthropod classes. The hemolymph of a crustacean, Libinia emarginata (Leach), has now been analyzed for JH-like compounds. Samples contained 0.003 to 0.030 nanogram of JH III per milliliter and 10 to 50 nanograms of methyl farnesoate per milliliter; methyl farnesoate is a compound structurally related to JH III that has JH bioactivity. Several tissues were examined for synthesis and secretion of JH-like compounds. Of these tissues, only the mandibular organs produced and secreted JH III and methyl farnesoate. However, microchemical analysis revealed that this JH III was racemic, and thus likely an artifactual oxidation product of methyl farnesoate. Secretion of methyl farnesoate was related to reproduction in females, with the highest rates observed in Libinia near the end of the ovarian cycle when oocyte growth and vitellogenesis are greatest. These results indicate that JH-like compounds such as methyl farnesoate have regulatory roles in crustaceans.

http://science.sciencemag.org/content/sci/235/4785/202.full.pdf

Identification of a juvenile hormone-like compound in a crustacean.

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

C. C. Reuter

Papers

Identification of a juvenile hormone-like compound in a crustacean.

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