Regulation Of Juvenile Hormone Biosynthesis Research Articles

Homeodomain Protein Scr Regulates the Transcription of Genes Involved in Juvenile Hormone Biosynthesis in the Silkworm.

The silkworm Dominant trimolting (Moltinism, M3) mutant undergoes three larval molts and exhibits precocious metamorphosis. In this study, we found that compared with the wild-type (WT) that undergoes four larval molts, both the juvenile hormone (JH) concentration and the expression of the JH-responsive gene Krüppel homolog 1 (Kr-h1) began to be greater in the second instar of the M3 mutant. A positional cloning analysis revealed that only the homeodomain transcription factor gene Sex combs reduced (Scr) is located in the genomic region that is tightly linked to the M3 locus. The expression level of the Scr gene in the brain-corpora cardiaca-corpora allata (Br-CC-CA) complex, which controls the synthesis of JH, was very low in the final larval instar of both the M3 and WT larvae, and exhibited a positive correlation with JH titer changes. Importantly, luciferase reporter analysis and electrophoretic mobility shift assay (EMSA) demonstrated that the Scr protein could promote the transcription of genes involved in JH biosynthesis by directly binding to the cis-regulatory elements (CREs) of homeodomain protein on their promoters. These results conclude that the homeodomain protein Scr is transcriptionally involved in the regulation of JH biosynthesis in the silkworm.

Identification and characterization of the NMDA receptor and its role in regulating reproduction in the cockroach Diploptera punctata.

The NMDA receptor (NMDAR) plays important roles in excitatory neurotransmission and in the regulation of reproduction in mammals. NMDAR in insects comprises two subunits, NR1 and NR2. In this study, we identified two NR1 paralogs and eleven NR2 alternatively spliced variants in the cockroach Diploptera punctata. This is the first report of NR1 paralogs in insects. The tissue distributions and expression profiles of DpNR1A, DpNR1B and DpNR2 in different tissues were also investigated. Previous studies have demonstrated NMDA-stimulated biosynthesis of juvenile hormone (JH) in the corpora allata through the influx of extracellular Ca(2+) in Diploptera punctata. However, our data show that the transcript levels of DpNR1A, DpNR1B and DpNR2 were low in the corpora allata. MK-801, a high-affinity antagonist of NMDAR, did not show any effect on JH biosynthesis in vitro. In addition, neither partial knockdown of DpNR2 nor in vivo treatment with a physiologically relevant dose of MK-801 resulted in any significant change in JH biosynthesis or basal oocyte growth. Injection of animals with a high dose of MK-801 (30 µg per animal per injection), which paralyzed the animals for 4-5 h, resulted in a significant decrease in JH biosynthesis on days 4 and 5. However, the reproductive events during the first gonadotrophic cycle in female D. punctata were unaffected. Thus, NMDAR does not appear to play important roles in the regulation of JH biosynthesis or mediate reproduction of female D. punctata.

Mode of action of allatostatins in the regulation of juvenile hormone biosynthesis in the cockroach, Diploptera punctata

The FGLamide allatostatins (FGL/ASTs) are a family of neuropeptides with pleiotropic functions, including the inhibition of juvenile hormone (JH) biosynthesis, vitellogenesis and muscle contraction. In the cockroach, Diploptera punctata, thirteen FGLa/ASTs and one allatostatin receptor (AstR) have been identified. However, the mode of action of ASTs in regulation of JH biosynthesis remains unclear. Here, we determined the tissue distribution of Dippu-AstR. And we expressed Dippu-AstR in vertebrate cell lines, and activated the receptor with the Dippu-ASTs. Our results show that all thirteen ASTs activated Dippu-AstR in a dose dependent manner, albeit with different potencies. Functional analysis of AstR in multiple cell lines demonstrated that activation of the AstR receptor resulted in elevated levels of Ca2+ and cAMP, which suggests that Dippu-AstR can act through the Gαq and Gαs protein pathways. The study on the target of AST action reveals that FGL/AST affects JH biosynthesis prior to the entry of acetyl-CoA into the JH biosynthetic pathway.

Role of the brain in photoperiodic regulation of juvenile hormone biosynthesis in the brown-winged green bug Plautia stali

We investigated the roles of the brain in photoperiodic regulation of juvenile hormone (JH) biosynthesis in Plautia stali (Heteroptera: Pentatomidae). Within 4days after transferring the adults from short-day to long-day conditions, the biosynthesis of juvenile hormone III skipped bisepoxide became higher than that under short-day conditions. When the corpus cardiacum–corpus allatum complex (CC–CA) was coincubated with different regions of the brain, JH biosynthetic activities were inhibited by a middle part of the brain, i.e., the brain excluding the optic lobes, extirpated from short-day and long-day females. Backfills from the CC–CA revealed three groups of somata in the middle part of the brain: 15–18 pairs of somata were stained in the pars intercerebralis, 9–10 pairs were stained in the pars lateralis, and five pairs were stained on the nervi corporis cardiaci 2. These results suggest that inhibitory molecules of JH biosynthesis are produced in the middle part of the brain, regardless of photoperiod, but their release is suppressed under long-day conditions, leading to an increase in JH biosynthetic activities. Further, some neurons with somata in the pars intercerebralis, in the pars lateralis, or on the nervi corporis cardiaci 2 might be involved in photoperiodic regulation of JH biosynthesis.

Characterisation and tissue distribution of the PISCF allatostatin receptor in the red flour beetle, Tribolium castaneum

The insect PISCF/allatostatins (ASTs) are pleiotropic peptides that are involved in the regulation of juvenile hormone biosynthesis, are myoinhibitory on the gut and the heart, and suppress feeding in various insects, but their roles in beetles are poorly understood. To provide further insight into the significance of PISCF/ASTs in beetles, the PISCF/AST receptor from Tribolium castaneum has been characterised and its tissue distribution determined. The biological activity of the T. castaneum PISCF/AST (Trica-AS) was also investigated.The Trica-AS receptor shows high sequence homology to other insect PISCF/AST receptors, which are related to the mammalian somatostatin/opioid receptors, a family of G protein-coupled receptors. The Trica-AS receptor was activated in a dose-dependent manner by both Trica-AS and T. castaneum allatostatin double C (Trica-ASTCC) as well as Manduca sexta-allatostatin (Manse-AS). Other allatoregulatory peptides (a FLG/AST, a MIP/AST and an allatotropin) and somatostatin14 were inactive on this receptor.Receptor transcript levels in tissues, determined by qRT-PCR, were highest in the head and the gut, with variable amounts in the fat body and reproductive organs. There were measurable differences in receptor levels of the head, fat body and reproductive organs between males and females. There was also a widespread distribution of Trica-AS in various tissues of T. castaneum. The Trica-AS peptide precursor was most abundant in the head and there was a significant difference between levels in the heads and reproductive organs of males and females.Whole mount immunocytochemistry localised Trica-AS in the median and lateral neurosecretory cells of the brain, in the corpus cardiacum and throughout the ventral nerve cord. The peptide was also present in midgut neurosecretory cells, but no immunostaining was detected in the reproductive organs or Malpighian tubules.The widespread distribution of both Trica-AS and its receptor suggest this peptide may have multiple roles in beetles. However, Trica-AS had no effect on the spontaneous contractions of the gut or ovaries of T. castaneum but this peptide did stimulate the release of proteases from the anterior midgut of another beetle, Tenebrio molitor. The activation of the Trica-AS receptor by Trica-ASTCC implies a physiological role for this peptide in beetles, which remains to be identified.

Stage-specific regulation of juvenile hormone biosynthesis by ecdysteroid in Bombyx mori

In the penultimate (4th) instar larvae of Bombyx mori, juvenile hormone (JH) synthesis by corpora allata (CA) fluctuates. When diet containing 20-hydroxyecdysone (20E) was fed, JH synthetic activity of the CA was first stimulated as the ecdysteroid titer increased, then suppressed slightly by the higher molting concentration of ecdysteroids (>250ng/ml). The overall JH biosynthetic activity was modulated by the expression of JH biosynthetic enzymes in the CA: primarily JH acid O-methyltransferase (JHAMT), isopentenyl diphosphate isomerase, and farnesyl diphosphate synthase 1. After the last (5th) larval ecdysis, the artificially increased high ecdysteroid level due to the 20E diet activated JH synthesis by the CA, which required intact nervous connections with the brain. A factor(s) from the 20E-activated brain controls mainly JHAMT and HMG Co-A reductase expression to stimulate the JH synthesis. In the normal last instar larvae, the ecdysteroid titer declines so that these activation mechanisms are absent; therefore the decline of the ecdysteroid titer after the final larval ecdysis is one of the factors which induces the cessation of the JH synthesis by CA.

Allatoregulatory peptides in Lepidoptera, structures, distribution and functions

Allatoregulatory peptides either inhibit (allatostatins) or stimulate (allatotropins) juvenile hormone (JH) synthesis by the corpora allata (CA) of insects. However, these peptides are pleitropic, the regulation of JH biosynthesis is not their only function. There are currently three allatostatin families (A-, B-, and C-type allatostatins) that inhibit JH biosynthesis, and two structurally unrelated allatotropins. The C-type allatostatin, characterised by its blocked N-terminus and a disulphide bridge between its two cysteine residues, was originally isolated from Manduca sexta. This peptide exists only in a single from in Lepidoptera and is the only peptide that has been shown to inhibit JH synthesis by the CA in vitro in this group of insects. The C-type allatostatin also inhibits spontaneous contractions of the foregut. The A-type allatostatins, which exist in multiple forms in a single insect, have also been characterised from Lepidoptera. This family of peptides does not appear to have any regulatory effect on JH biosynthesis, but does inhibit foregut muscle contractions. Two structurally unrelated allatotropins stimulate JH biosynthesis in Lepidoptera. The first was identified in M. sexta (Manse-AT) and occurs in other moths. The second (Spofr AT2) has only been identified in Spodoptera frugiperda. Manduca sexta allatotropin also stimulates heart muscle contractions and gut peristalsis, and inhibits ion transport across the midgut of larval M. sexta. The C-terminal (amide) pentapeptide of Manse-AT is important for JH biosynthesis activity. The most active conformation of Manse-AS requires the disulphide bridge, although the aromatic residues also have a significant effect on biological activity. Both A- and C-type allatostatins and Manse-AT are localised in neurosecretory cells of the brain and are present in the corpora cardiaca, CA and ventral nerve cord, although variations in localisation exist in different moths and at different stages of development. The presence of Manse-AS and Manse-AT in the CA correlates with the biological activity of these peptides on JH biosynthesis. There is currently no explanation for the presence of A-type allatostatins in the CA. The three peptide types are also co-localised in neurosecretory cells of the frontal ganglion, and are present in the recurrent nerve that supplies the muscles of the gut, particularly the crop and stomodeal valve, in agreement with their role in the regulation of gut peristalsis. There is also evidence that they are expressed in the midgut and reproductive tissues.

Biochemical, Molecular, and Functional Characterization of PISCF-Allatostatin, a Regulator of Juvenile Hormone Biosynthesis in the Mosquito Aedes aegypti

Aedes aegypti PISCF-allatostatin or allatostatin-C (Ae-AS-C) was isolated using a combination of high performance liquid chromatography and enzyme-linked immunosorbent assay (ELISA). The matrix-assisted laser desorption/ionization time-of-flight (TOF) mass spectrum of positive ELISA fractions revealed a molecular mass of 1919.0 Da, in agreement with the sequence qIRYRQCYFNPISCF, with bridged cysteines. This sequence was confirmed by matrix-assisted laser desorption/ionization tandem TOF/TOF mass spectrometry analysis. The corresponding Ae-AS-C cDNA was amplified by PCR, and the sequence of the peptide was confirmed. An in vitro radiochemical assay was used to study the inhibitory effect of synthetic Ae-AS-C on juvenile hormone biosynthesis by the isolated corpora allata (CA) of adult female A. aegypti. The inhibitory action of synthetic Ae-AS-C was dose-dependent; with a maximum at 10(-9) m. Ae-AS-C showed no inhibitory activity in the presence of farnesoic acid, an immediate precursor of juvenile hormone, indicating that the Ae-AS-C target is located before the formation of farnesoic acid in the pathway. The sensitivity of the CA to inhibition by Ae-AS-C in the in vitro assay varied during the adult life; the CA was most sensitive during periods of low synthetic activity. In addition, the levels of Ae-AS-C in the brain were studied using ELISA and reached a maximum at 3 days after eclosion. These studies suggest that Ae-AS-C is an important regulator of CA activity in A. aegypti.

Molecular characterization of a cDNA from the true armyworm Pseudaletia unipuncta encoding Manduca sexta allatotropin peptide

Allatotropin (AT) is an insect neuropeptide isolated from the tobacco hornworm, Manduca sexta, stimulates juvenile hormone (JH) biosynthesis by the corpora allata. A cDNA isolated from the true armyworm, Pseudaletia unipuncta, encodes a 135 amino acid AT precursor peptide which contains the AT peptide, with processing sites necessary for its endoproteolytic cleavage and amidation, plus two additional peptides of unknown function. The encoded AT peptide is identical to that isolated from M. sexta and Agrius convolvuli. Southern blot analysis indicated that AT is a single copy gene per haploid genome and is present in two allelic forms. A single transcript of approximately 1.5 kilobases was detected by northern blot analysis. The expression of the AT gene was analyzed during development from sixth instar larvae to five day-old moths. Initial expression was observed in late pupae and this expression was maintained throughout the adult stages in both sexes. In one day-old moths, expression was at its lowest level of the stages that express AT mRNA but levels increased in day 3 and day 5 adults. This pattern of AT expression in adult P. unipuncta moths mirrors that of JH biosynthesis and supports the notion that AT may act in the adult stages. Immunohistochemistry and in situ hybridization revealed that AT expression was localized to numerous structures of the nervous system, suggesting that AT may have functions distinct from regulation of JH biosynthesis.

Insect juvenile hormone: from "status quo" to high society.

Juvenile hormone (JH) exerts pleiotropic functions during insect life cycles. The regulation of JH biosynthesis by neuropeptides and biogenic amines, as well as the transport of JH by specific binding proteins is now well understood. In contrast, comprehending its mode of action on target organs is still hampered by the difficulties in isolating specific receptors. In concert with ecdysteroids, JH orchestrates molting and metamorphosis, and its modulatory function in molting processes has gained it the attribute "status quo" hormone. Whereas the metamorphic role of JH appears to have been widely conserved, its role in reproduction has been subject to many modifications. In many species, JH stimulates vitellogenin synthesis and uptake. In mosquitoes, however, this function has been transferred to ecdysteroids, and JH primes the ecdysteroid response of developing follicles. As reproduction includes a variety of specific behaviors, including migration and diapause, JH has come to function as a master regulator in insect reproduction. The peak of pleiotropy was definitely reached in insects exhibiting facultative polymorphisms. In wing-dimorphic crickets, differential activation of JH esterase determines wing length. The evolution of sociality in Isoptera and Hymenoptera has also extensively relied on JH. In primitively social wasps and bumble bees, JH integrates dominance position with reproductive status. In highly social insects, such as the honey bee, JH has lost its gonadotropic role and now regulates division of labor in the worker caste. Its metamorphic role has been extensively explored in the morphological differentiation of queens and workers, and in the generation of worker polymorphism, such as observed in ants.

Regulation of Juvenile hormone biosynthesis by ecdysteroid levels during the early stages of the last two larval instars of Bombyx mori

Juvenile hormone (JH), produced by the corpora allata (CA), is critical for the regulation of insect postembryonic development. In the present study, a radiochemical assay was used to examine developmental changes in the JH biosynthetic rate in vitro in Bombyx mori; its regulation by the ecdysteroid levels in the haemolymph during the early stages of the last two larval instars was clarified. During the early stages of the penultimate larval instar, the ecdysteroid titres were maintained at levels ranging from 42 to 57 ng ml , the JH biosynthetic rate fluctuated but was maintained at detectable levels. During the early stages of the last larval instar, the ecdysteroid titres decreased to very low levels (3–12 ng ml ), CA ceased to produce JH midway through the instar. The ecdysteroid levels during the early stages of these two larval instars were artificially changed by various experimental manipulations, then, changes in the JH biosynthetic rate were assessed and the subsequent development of larvae was carefully examined. We concluded that whether CA continued to produce JH or became inactive during subsequent development is controlled by the ecdysteroid levels present in the haemolymph. Low ecdysteroid levels are a prerequisite for CA to become inactive and thus an important developmental signal preceding larval-pupal transformation. Incubation of isolated CA from newly-ecdysed last instar larvae with 20-hydroxyecdysone revealed that 20-hydroxyecdysone directly stimulates CA activity.

Role of second messengers in the regulation of juvenile hormone production in insects, with particular emphasis on calcium and phosphoinositide signaling

Juvenile hormone (JH) biosynthesis is regulated by both peptidergic and aminergic inputs. Depending upon the species and developmental stage, these signals may be either inhibitory or stimulatory (allatostatins and allatotropins). Signal transduction within corpus allatum cells occurs by way of known second messengers, including the cyclic nucleotides, Ca2+, and the phosphoinositides. We review the role of signal transduction in the regulation of JH biosynthesis in the locust, Locusta migratoria, the hornworm, Manduca sexta, and the cockroach, Diploptera punctata. Differences in signal transduction between the species reflect in part differences in the signals which regulate the corpus allatum. For example, JH biosynthesis in locusts appears to be regulated principally by allatotropic signals, whereas in the cockroach allatostatic signals appear to predominate. In M. sexta, both types of signals appear to function and are stage-dependent. This may reflect the complex nature of the juvenile hormone products in this species, whereas in locusts and cockroaches only JH III is produced. Modulation of intracellular calcium (CA2+) levels by drugs (ionophores, Ca2+ chelators and releasing agents, CA2+ channel blockers) or depolarizing agents including current injection dramatically alters JH biosynthesis, as do agents that activate the phosphoinositide pathway. Modulation of intracellular cAMP levels is associated with changes in JH production, with increases in JH biosynthesis occurring as a consequence of the stimulation of the adenylate cyclase system in locusts but with an inhibition of JH biosynthesis in cockroaches. The situation in M. sexta is more complex and appears to be both stage- and product-dependent. The effects of second messengers in the three species differ, probably as a consequence of the differences in the peptide signals that regulate JH biosynthesis and in the intrinsic state of the corpora allata (either switched on or switched off, in the absence of external signals). © 1996 Wiley-Liss, Inc.

Role of second messengers in the regulation of juvenile hormone production in insects, with particular emphasis on calcium and phosphoinositide signaling

Juvenile hormone (JH) biosynthesis is regulated by both peptidergic and aminergic inputs. Depending upon the species and developmental stage, these signals may be either inhibitory or stimulatory (allatostatins and allatotropins). Signal transduction within corpus allatum cells occurs by way of known second messengers, including the cyclic nucleotides, Ca2+, and the phosphoinositides. We review the role of signal transduction in the regulation of JH biosynthesis in the locust, Locusta migratoria, the hornworm, Manduca sexta, and the cockroach, Diploptera punctata. Differences in signal transduction between the species reflect in part differences in the signals which regulate the corpus allatum. For example, JH biosynthesis in locusts appears to be regulated principally by allatotropic signals, whereas in the cockroach allatostatic signals appear to predominate. In M. sexta, both types of signals appear to function and are stage-dependent. This may reflect the complex nature of the juvenile hormone products in this species, whereas in locusts and cockroaches only JH III is produced. Modulation of intracellular calcium (CA2+) levels by drugs (ionophores, Ca2+ chelators and releasing agents, CA2+ channel blockers) or depolarizing agents including current injection dramatically alters JH biosynthesis, as do agents that activate the phosphoinositide pathway. Modulation of intracellular cAMP levels is associated with changes in JH production, with increases in JH biosynthesis occurring as a consequence of the stimulation of the adenylate cyclase system in locusts but with an inhibition of JH biosynthesis in cockroaches. The situation in M. sexta is more complex and appears to be both stage- and product-dependent. The effects of second messengers in the three species differ, probably as a consequence of the differences in the peptide signals that regulate JH biosynthesis and in the intrinsic state of the corpora allata (either switched on or switched off, in the absence of external signals). © 1996 Wiley-Liss, Inc.

Developmental regulation of juvenile hormone biosynthesis by the corpora allata of Bombyx mori

Abstract The synthesis and secretion in vitro of juvenile hormone (JH) by corpora allata (CA) isolated from larvae of the silkworm, Bombyx mori were quantified by a radiochemical assay. The data indicated that, during the third and fourth stadia, the biosynthetic rate fluctuated but was always maintained above detectable levels. During the last larval stadium, the biosynthetic rate was 0.12 pmol/pr(gland pair)/hr on day 0, then steadily declined and became undetectable after day 3. A comparison of JH biosynthetic rates by brain-corpora cardiaca-corpora allata complexes (BR-CC-CA) with those by isolated CA during the last two larval stadia was conducted and results showed that the brain modulates CA activity in different ways according to different developmental stages. High pressure liquid chromatographic (HPLC) analysis was conducted on the incorporated product of CA at specific developmental stages, and results showed that the major product of the CA of silkworm larvae was JH I with small portions of JH II and traces of JH III. The effects of KK-42 application on CA activity were also examined.

Stimulatory effect of octopamine on juvenile hormone biosynthesis in honey bees ( Apis mellifera): Physiological and immunocytochemical evidence

The effect of octopamine on the activity of corpora allata of adult worker honey bees has been examined in vitro and correlated to the local distribution of this biogenic amine in brain and retrocerebral complex as studied immunocytochemically by means of an highly specific antiserum. Octopamine causes a dose-dependent increase in juvenile hormone release from corpora allata. Maximum increase is obtained with concentrations of 10 −6 M in nurse and foraging bees by 45.3 or 32.3%, respectively. Octopamine-like immunoreactivity occurs in about 45 somata of the median neurosecretory cells in the pars intercerebralis of the bee brain. They project via immunopositive nervus corporis cardiaci I into the corpora cardiaca, where interspersed varicose structures and 8–10 cell bodies in the ventral part of this gland are stained. A network of immunoreactive fine varicose nerve fibres surrounds each gland cell of the corpora allata. Immunoreactivity in these neuronal structures is detectable if bees were starved over night, a condition in which corpora allata elicit the highest juvenile hormone production ever observed in bees. Both, the stimulatory effect of octopamine and the presence of immunoreactive nerve fibers in the corpora allata, strongly indicate a physiological role of this biogenic amine in the regulation of juvenile hormone biosynthesis in adult honey bees.

Sex-specific developmental profiles of juvenile hormone synthesis in honey bee larvae.

Juvenile hormone synthesis in drone larvae of the honey bee was measured by an in vitro radiochemical assay. The developmental profile of corpora allata activity in male larvae showed considerable differences from queen larvae, the presumptive reproductive females, and was comparable to workers, the sterile female morph. Drone and worker larvae, however, differed drastically in the regulation of juvenile hormone biosynthesis, as revealed by the addition of farnesoic acid to the culture medium. This precursor stimulated juvenile hormone synthesis of drone glands nearly eightfold, whereas in worker larvae it is known to lead to an accumulation of methyl farnesoate. The sex-specific differences in endocrine activity indicate a role for juvenile hormone in the expression of genetically determined sexually dimorphic characters during metamorphosis, a role not currently accounted for in models describing endocrine regulation of insect development.

Effect of cobalt and other divalent cations on oöcyte development of the black blowfly, Phormia regina (Meigen)

Results showed that injections of the divalent cation cobalt, a calcium channel blocker, at effective haemolymph concentrations of 2.1, 3.4 or 5.0 mM, immediately prior to liver feeding, retarded or inhibited egg development by influencing vitellogenin uptake in Phormia regina. Topical application of methoprene (a juvenile hormone analogue) to cobalt-injected flies partially restored the otherwise inhibited egg development. Since vitellogenin uptake in this fly is controlled by juvenile hormone, cobalt may affect oöcyte development at least partly through its effect on juvenile hormone biosynthesis. Rates of juvenile hormone biosynthesis by the corpus allatum, in vitro, in cobalt-injected flies fell into three levels of 0.48 ± 0.01, 0.72 ± 0.12 and 0.97 ± 0.08 pmol/gland pair/h. These three levels of rates of juvenile hormone biosynthesis corresponded well with the three categories of ovary development observed in cobalt-injected flies: undeveloped, partially developed and fully developed. In comparison, the rates of juvenile hormone biosynthesis were 0.03 ± 0.00, 1.16 ± 0.08 and 1.23 ± 0.10 pmol/gland pair/h for sugar-fed, liver-fed, and liver-fed but water-injected control flies, respectively. Effects or lack of effects of several different calcium-replacement divalent cations and a dihydropyridine calcium channel blocker (i.e. nifedipine) on oöcyte development in P. regina suggested that calcium channels of the corpora allata may be involved in the regulation of juvenile hormone biosynthesis, which then affected oöcyte development.

Evidence for regulation of juvenile hormone biosynthesis operating before mevalonate in locust corpora allata

Exogenous mevalonate poorly stimulated juvenile hormone III (JH-3) biosynthesis by corpora allata from Locusta migratoria. However, mevalonolactone strongly stimulated glands from different physiological states and fully restored JH synthesis in mevinolin-treated glands. Asymmetry in spontaneous rate of JH release was abolished by exogenous mevalonolactone. After transection of nervus corporis allati 1 (NCA-1), the rate of mevalonolactone-stimulated JH synthesis was maintained at the preoperative levels although the spontaneous rate of JH biosynthesis decreased rapidly. These results suggest that the spontaneous asymmetry of JH biosynthesis and the low rate of JH biosynthesis by denervated corpora allata both result from non-stimulation or inhibition acting on the JH pathway before the utilisation of mevalonate.

Developmental changes and second messenger modulation of the electrical properties of cells of the cockroach corpora allata

The duration of evoked action potentials in the cells of the corpora allata of recently emerged adult mated female cockroaches was dramatically increased following replacement of calcium ions by barium ions in the bathing saline. The magnitude of this increase was age-dependent. Furthermore, following exposure of corpora allata to barium, spontaneous action potentials (approx. 10–40 mV in amplitude) and small depolarizing potentials (approx. 2–5 mV in amplitude) were observed that were never seen in the absence of barium. This suggests that barium increases the excitability of the corpora allata. 8-bromo-cyclic AMP and the phorbol ester, phorbol 12,13-dibutyrate (PDBu), both increased the duration of barium action potentials in corpora allata from day-1 and day-6 females. However, 8-bromo-cyclic GMP, and the nonspecific protein kinase inhibitor H7 both reduced the barium action potential in day-1 corpora allata but had no significant effect in day-6 corpora allata. Furthemore, the inactive phorbol ester 4a-phorbol 12,13-didecanoate (PDD) did not significantly affect the barium action potential duration in day-1 or day-6 corpora allata, suggesting that PDBu is acting through phospholipid/calcium-dependent protein kinase C and not nonspecifically. 8-Br-cAMP and protein kinase C appear to modulate the electrophysiological properties of the cell membranes of the corpora allata, which suggests that they may modulate calcium influx. In addition, cAMP, protein kinase C and calcium have previously been implicated in the regulation of juvenile hormone biosynthesis. In view of the effects of cAMP and protein kinase C on both membrane properties and juvenile hormone biosynthesis, the cell membrane may be a site for integration of the calcium, cAMP and protein kinase C second messenger systems involved in the regulation of juvenile hormone biosynthesis. Furthermore, because juvenile hormone biosynthesis undergoes cyclical changes in adult mated female cockroaches and there are developmental changes in the electrical properties of the corpora allata, such changes may be important in the regulation of juvenile hormone biosynthesis, possibly by altering calcium influx.

Correlation among corpus allatum volume, cell size, and juvenile hormone biosynthesis in ovariectomized adult Blattella germanica

AbstractThe corpora allata (CA) of both intact and ovariectomized Blattella germanica adult females exhibited a high degree of bilateral symmetry in the rate of juvenile hormone (JH) biosynthesis, the mean size of CA cells, and gland volume (81.3%, 98.3%, and 100% respectively with less than a twofold difference between the two glands in CA pairs). This permitted us to split each CA pair randomly, measure JH biosynthesis in one gland, and dissociate the other gland into a cell suspension in which the size of CA cells was measured. In ovariectomized females, changes in CA volume and the spontaneous and farnesoic acid (FA)‐stimulated rates of JH biosynthesis, measured from the same glands, were well correlated (r = 0.78, for both correlations). Similarly, the mean volume of CA cells in one gland increased in relation to increases in both the spontaneous and FA‐stimulated rates of JH biosynthesis by the contralateral member of the pair (r = 0.83 and r = 0.91, respectively). Concurrent changes in CA cell size and activity suggest that in the CA of B. germanica cellular growth and degradation are involved in the regulation of JH biosynthesis.