Corpora allata

One of the insect neurohormones, the activation hormone, controls the secretion of the corpora allata, paired glands that synthesize the juvenile hormone (Fig. 22-4) in insect larvae. While the structure of the juvenile hormone varies somewhat with species, it is usually a polyprenyl ester. A specific binding protein provides the hormone with protection from degrada-tive enzymes. However, in the tobacco homworm an esterase, able to hydrolyze the protein-bound juvenile hormone, is produced at the start of pupal differentiation.354 The exact mechanism of action of juvenile hormones has been difficult to determine. However, it affects polyamine synthesis.355 356... 

A related role of the insect corpora allata is to store and release the prothoracicotropic hormone, a... 

Sreng L., Leoncini I. and Clement J. L. (1999) Regulation of sex pheromone production in the male Nauphoeta cinerea cockroach role of brain extracts, corpora allata (CA), and juvenile hormone (JH). Arch. Insect Biochem. Physiol. 40, 165-172. 

Hollander A. L. and Yin C.-M. (1985) Lack of humoral control in calling and pheromone release by brain, corpora cardiaca, corpora allata and ovaries of the female gypsy moth, Lymantria dispar (L.). J. Insect Physiol. 31, 159-163. 

Park Y. I. and Ramaswamy S. B. (1998) Role of brain, ventral nerve cord and corpora cardiaca-corpora allata complex in the reproductive behavior of female tobacco budworm (Lepidoptera Noctuidae). Ann. Entomol. Soc. Am. 91, 329-334. 

Judy K. J., Schooley D. A., Troetschler R. G., Jennings R. C., Bergot B. J. and Hall M. S. (1975) Juvenile hormone production by corpora allata of Tenebrio molitor in vitro. Life Sciences 16, 1059-1066. 

Osorio S., Piulachs M. D. and Belles X. (1998) Feeding and activation of the corpora allata in the cockroach Blattella germanica (L.) (Dictyoptera, Blattellidae). J. Insect Physiol. 44, 31-38. 

Duportets L., Dufour M. C., Couillaud F. and Gadenne C. (1998) Biosynthetic activity of corpora allata, growth of sex accessory glands and mating in the male moth Agrotis ipsilon (Hufnagel). J. Exp. Biol. 201, 2425-2432. 

Brindle, P. A., Schooley, D.A., Tsai, L. and Baker, F.C. (1988). Comaparative metabolism of branched-chain amino acids to precursors of juvenile hormone biogenesis in corpora allata of lepidopterous versus non-lepidopterous insects. J. Biol. Chem., 263, 10653-10657. 

Several authors have investigated the role of juvenile hormone (JH) in hydrocarbon signatures. Sledge et al. (2004) performed one such study based on measuring the size of the corpora allata as an indicator of JH levels. Since caste determination depends strictly on the colony social structure, it can be assumed that topical JH application mimics natural caste development and thus modifies the cuticular caste-specific odor. Based on this assumption,... 

ROseler, P. F ROseler, I. and Vanhonk, C. G. J. (1981). Evidence for inhibition of corpora allata activity in workers of Bombus terrestris by a pheromone from the queen s mandibular glands. Experientia, 37, 348-351. 

The CHCs of the blow-fly Phormia regina are complex mixtures of saturated n-, monomethyl- and dimethylalkanes with 23-33 carbon atoms. These CHCs do not appear to change with age or diet, and differ only slightly between the sexes (Byrne et al, 1995 Stoffolano et al., 1997). Males show the same strong copulatory response to dummies covered with the extract of either sex but a very reduced response to hexane-washed flies (Stoffolano et al., 1997). In Calliphora vomitoria, the situation is less clear. Ablation of the female corpora allata or of the ovaries leads to an increase in the proportion of monomethylalkanes. However, these two procedures induce divergent effects on male attraction. Moreover, when hydrocarbon production was unchanged, male attraction was... 

In moving to other classes of JH analogs, major departures from the farnesane skeleton have been reported in the form of phenyl ethers (22, Z3,2 ), cyclohexenes such as juvabione (25), and small peptides (26) as an extreme case of completely selective action on one family of bugs. The latter compounds are most remarkable for the pronounced differential activity of their optical enantiomers, in which one antipode is several thousand times more active biologically than the other (2 7). In connection with the peptides, it should be noted that there is no formal proof that these compounds exert their action as true mimics of juvenile hormones at the target tissue level. One may well ask whether these peptides act directly on the corpora allata glands as allatotropins. 

These inhibitors would be classified as anti-juvenile hormones and could be expected to show selective action on insects as a class. Such analogs are by no means just around the corner since at least two important properties that they should possess may be difficult to build into small organic molecules suitable for pest control. These properties are the ability to withstand general metabolic inactivation while retaining the ability to inhibit irreversibly the target enzymes of the corpus allatum and the property to accumulate selectively in corpora allata, a physically small target, so as to offset dilution in the general body cavity. 

A further complication arose when it was discovered that in the Mediterranean fruit fly Ceratitis capitata (Diptera Trypetidae) the corpora allata of adult virgin females produce, in addition to JHB-3, smaller amounts of methyl palmitate and less of JH III.97 Mated females produced much less methyl palmitate. It is suggested that methyl palmitate may be a default product of methylation, in the absence of JH, but it does not rule out the possibility that it also participates in some way in reproductive maturation and control, because its presence is correlated with the period of nonreceptivity toward mating in adult females of... 

Much interest has been shown in the biosynthesis of insect juvenile hormones (62 R1, R2 = Me or Et). In adult male moths, [l-14C]propionate was specifically incorporated into juvenile hormone I [JH-1, (62 R1 = R2 = Et)], and tracer was only found at, and equally distributed between, C-7 and C-ll.90 Application of [2-14C]-and [3-14C]-propionate led to extensive randomization of label, which suggests that C-2 and C-3 formed in propionate catabolism can be re-used as smaller fragments, whilst C-l is either removed from propionate in a metabolically active form or is highly diluted. Ternary complexes of brain, corpora cardiaca, and corpora allata from the tobacco budworm Heliothis virescens produced labelled JH-I and JH-II (62 R1 = Et, R2 = Me) when incubated with L-[Me-14C]methionine or sodium [l-l4C]propionate.91 Partial degradation of the juvenile hormones showed that in JH-I portions a and /3 (62) had incorporated one atom of tracer from each propionate, whereas fraction y was unlabelled, and in JH-II only fraction a was... 

Experiments have been described94 in which small amounts of tracer have been incorporated into juvenile hormones from amino-acid precursors under conditions where the intracellular pool size of these precursors may be determined by routine methods, and an assay procedure has been developed95 by which the esterification of farnesenic acid with the methyl group from methionine, and the 10,11-epoxidation of the resultant ester to yield JH-III, can be measured in corpora allata of the adult female Schistocerca gregaria. 

The juvenile hormones are synthesized and rapidly released into the hemolymph from the neuroendocrine glands known as the corpora allata synthesis appears to be under control of a hormone originating in the brain. 

The epoxidase catalyzing the 10,11-epoxidation of methyl farnesoate in homogenates of corpora allata from Locusta miqratoria has been studied in detail and has been shown to be a cytochrome P-450-mediated monooxygenase associated with the microsomal fraction. The enzyme is strictly dependent on NADPH and requires oxygen (36). It is sensitive to inhibition by carbon monoxide (36) and to offier compounds such as methyl enedioxyphenyl compounds and imidazoles that are well established inhibitors of the cytochrome P-450-mediated monooxygenases involved in xenobiotic metabolism (37-39). 

Phvtoluvenolds. Wigglesworth (JL) demonstrated that a hormone secreted by the insect corpora allata was responsible for the control of differentiation in immature insects and reproduction in adult female insects. Williams (3) prepared an active extract of this hormone from adult male cecropia moths and called it "juvenile hormone". We were able to derive sufficient knowledge of the chemistry of the juvenile hormone from the study of the active cecropia extract to synthesize JH III Q). Seven years later its presence as a natural hormone in the tobacco hornworm was confirmed Ci). Three other analogous juvenile hormones (JH 0, I, II) have been found to occur only in lepidoptera (5, ., 2.) (Figure 1). Juvenile hormone III is the principal juvenile hormone of insects and has been demonstrated in all of the insect taxa investigated. 

Mode of action studies reveal that the corpora allata are destroyed following exposure to the precocenes (59=61). Metabolism studies indicated that precocene was rapidly oxidized and hydrated to the 3,4-dihydrodiol and that the epoxide appeared to be an activated intermediate C62). Recent evidence indicates that the epoxide is an alkylating agent which destroys the corpora allata terminating juvenile hormone production ( 3, 1). 

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