Juvenile hormone acid and ecdysteroid together induce competence for metamorphosis of the Verson's gland in Manduca sexta

Gene expression in Verson's glands of the fall armyworm suggests their role in molting and immunity

Verson's glands are segmental pairs of dermal glands attached to the epidermis in lepidopteran larvae. They produce macromolecules during intermolt period and empty them during each molt. Morphological, histochemical, developmental, and protein analysis studies have been conducted to determine the functions of Verson's glands. However, the exact role of Verson's glands remains unclear. In our previous study, a strain of transgenic fall armyworm, Spdoptera frugiperda expressing green fluorescence protein (GFP) and Systemic RNA interference defective protein 1 (SID1) from Caenorhabditis elegans was established to improve RNA interference (RNAi) efficiency. Unexpectedly, we found that GFP fluorescence was significantly brighter in Verson's glands than in other tissues. Also, RNAi efficiency improved more in Verson's glands than in other tissues. We took advantage of improved RNAi efficiency to explore the function of Verson's glands. RNA-seq analysis revealed that genes highly expressed in Verson's glands code for cuticular proteins, molting fluid proteins, hemolymph proteins, and antimicrobial peptides. Injection of dsRNA targeting essential genes, inhibitor of apoptosis (IAP), Actin, and vacuolar-type ATPase (VATPase) interfered with Verson's glands growth. These results revealed that Verson's glands may contribute to hemolymph, cuticle, molting fluid, and immune response during molting. This study also provide useful tools for future research in identifying the physiological role of Verson's glands in lepidopteran insects.

Multiple miRNAs jointly regulate the biosynthesis of ecdysteroid in the holometabolous insects, Chilo suppressalis

The accurate rise and fall of active hormones is important for insect development. The ecdysteroids must be cleared in a timely manner. However, the mechanism of suppressing the ecdysteroid biosynthesis at the right time remains unclear. Here, we sequenced a small RNA library of Chilo suppressalis and identified 300 miRNAs in this notorious rice insect pest. Microarray analysis yielded 54 differentially expressed miRNAs during metamorphosis development. Target prediction and in vitro dual-luciferase assays confirmed that seven miRNAs (two conserved and five novel miRNAs) jointly targeted three Halloween genes in the ecdysteroid biosynthesis pathway. Overexpression of these seven miRNAs reduced the titer of 20-hydroxyecdysone (20E), induced mortality, and retarded development, which could be rescued by treatment with 20E. Comparative analysis indicated that the miRNA regulation of metamorphosis development is a conserved process but that the miRNAs involved are highly divergent. In all, we present evidence that both conserved and lineage-specific miRNAs have crucial roles in regulating development in insects by controlling ecdysteroid biosynthesis, which is important for ensuring developmental convergence and evolutionary diversity.

CHARACTERIZATION AND FUNCTIONAL STUDY OF A PUTATIVE JUVENILE HORMONE DIOL KINASE IN THE COLORADO POTATO BEETLE Leptinotarsa decemlineata (Say)

Juvenile hormone diol kinase (JHDK) is an enzyme involved in JH degradation. In the present article, a putative JHDK cDNA (LdJHDK) was cloned from the Colorado potato beetle Leptinotarsa decemlineata. The cDNA consists of 814 bp, containing a 555 bp open reading frame encoding a 184 amino acid protein. LdJHDK reveals a high degree of identity to the previously reported insect JHDKs. It possesses three conserved purine nucleotide-binding elements, and contains three EF-hand motifs (helix-loop-helix structural domains). LdJHDK mRNA was mainly detected in hindgut and Malpighian tubules. Besides, a trace amount of LdJHDK mRNA was also found in thoracic muscles, brain-corpora cardiaca-corpora allata complex, foregut, midgut, ventral ganglia, fat body, epidermis, and hemocytes. Moreover, LdJHDK was expressed throughout all developmental stages. Within the first, second, and third larval instar, the expression levels of LdJHDK were higher just before and right after the molt, and were lower in the intermediate instar. In the fourth larval instar, the highest peak of LdJHDK occurred 56 h after ecdysis. Ingestion of double-stranded RNA (dsRNA) against LdJHDK successfully knocked down the target gene, increased JH titer, and significantly upregulated LdKr-h1 mRNA level. Knockdown of LdJHDK significantly impaired adult emergence. Thus, we provide a line of experimental evidence in L. decemlineata to support that LdJHDK encodes function protein involved in JH degradation.

Juvenile hormone (JH) esterase activity but not JH epoxide hydrolase activity is downregulated in larval Adoxophyes honmai following nucleopolyhedroviruses infection

Juvenile hormones (JHs) and ecdysteroids are critical insect developmental hormones. JH esterase (JHE) and JH epoxide hydrolase (JHEH) are JH-selective enzymes that metabolize JH and thus regulate the titer of JH. Baculoviruses are known to alter host endocrine regulation. The nucleopolyhedroviruses, AdhoNPV and AdorNPV, are known to have slow and fast killing activity against Adoxophyes honmai (Lepidoptera: Tortricidae), respectively. Here we found that when penultimate (4th) instar A. honmai are inoculated with AdhoNPV or AdorNPV, the mean survival time is 9.7 and 8.2 days, respectively. The larvae molted once but did not pupate. The AdhoNPV- or AdorNPV-infected larvae did not show a dramatic increase in JHE activity as was found in mock-infected larvae, instead they showed a marked decrease in JHE activity. In contrast, both viral infections had no effect on JHEH activity. In order to further characterize the JHE activity, the JHE-coding sequence of A. honmai (ahjhe) was cloned and confirmed to encode a biologically active JHE. Quantitative real-time PCR analysis of ahjhe expression in 4th and 5th instar A. honmai revealed that AdhoNPV and AdorNPV are able to reduce ahjhe expression levels.

Juvenile hormone esterase: biochemistry and structure

Normal insect development requires a precisely timed, precipitous drop in hemolymph juvenile hormone (JH) titer. This drop occurs through a coordinated halt in JH biosynthesis and increase in JH metabolism. In many species, JH esterase (JHE) is critical for metabolism of the resonance-stabilized methyl ester of JH. JHE metabolizes JH with a high kcat/KM ratio that results primarily from an exceptionally low KM. Here we review the biochemistry and structure of authentic and recombinant JHEs from six insect orders, and present updated diagnostic criteria that help to distinguish JHEs from other carboxylesterases. The use of a JHE-encoding gene to improve the insecticidal efficacy of biopesticides is also discussed.

Role of allatostatin-like factors from the brain of Tenebrio molitor females

The effect of brain extract from females of freshly emerged Tenebrio molitor on ovary, oocyte development, total protein content of hemolymph, and ovary was studied in 4-day-old adult mealworm females. Injections of extracts of 2-brain equivalents into intact (unligatured) Tenebrio females did not affect ovarian and oocyte development. Injections of ligated females, however, with 2-brain equivalents on day 1 and 2 after adult emergence strongly inhibited ovarian growth and oocyte development. At day 4, ligated and injected females did not develop their ovaries and pre-vitellogenic oocytes were not found. The changes in ovarian development correlated with an increase in the concentration of soluble proteins in the hemolymph as compared with the saline-injected controls. Additionally, a strong reduction of total protein content in ovarian tissue was observed. Reverse phase HPLC separation of a methanolic brain extract of T. molitor females showed that fraction 5 has a similar retention time to synthetic cockroach allatostatin. Fraction 5 was eluted at 12.88 min, which was closest to the internal standard Dippu-AST I, which eluted at 12.77 min. An ELISA of fraction 5 from the methanolic brain extract using antibodies against allatostatins Grybi-AST A1 and Grybi-AST B1 from cricket Gryllus bimaculatus showed that fraction 5 cross-reacted with Grybi-AST A1 antibodies. The cross-reactivity was similar to the synthetic allatostatin from D. punctata, which was used as a positive control. These observations demonstrate a possible role for allatostatin-like brain factor(s) in regulating the reproductive cycle of Tenebrio molitor.

Juvenile hormone esterase activity in the pupating and diapausing larvae of Sesamia nonagrioides

The development of the Mediterranean corn borer, Sesamia nonagrioides, under long-day (LD) photoperiod is associated with juvenile hormone (JH) decline and pupation in the 5th or 6th larval instar. The larvae grown under short-day (SD) conditions maintain a moderate JH titer and enter diapause during which they undergo several extra larval molts. Both types of larvae exhibit similar levels of juvenile hormone esterase (JHE) activity that increases in each instar during the period of low ecdysteroid titer and drops when the titer rises to a molt-inducing peak. A suppression of JHE activity within 24h after application of an ecdysteroid agonist suggests that the drop of activity is a rapid and possibly direct response to ecdysteroids or their agonist. Esterase inhibitor 3-octylthio-1,1,1-trifluoro-2-propanone (OTFP) suppressed more than 98% of the JHE activity without affecting pupation timing and adult development. The data indicate that JHE is not crucial for the switch between larval development, diapause, and metamorphosis in S. nonagrioides.

Juvenile hormone diol kinase, a calcium-binding protein with kinase activity, from the silkworm, Bombyx mori

Juvenile hormone (JH) diol kinase (JHDK) is an important enzyme involved in the JH degradation pathway. Bombyx mori (Bommo)-JHDK cDNA (637bp) contains an open reading frame encoding a 183-amino acid protein, which reveals a high degree of identity to the two previously reported JHDKs. JHDK is similar to GTP-binding proteins with three conserved sequence elements involved in purine nucleotide binding, contains eight alpha-helices and three EF-hand motifs, and resembles the three-dimensional model of 2SCP and some other calcium-binding proteins. The Bommo-JHDK gene has only a single copy in the silkworm haploid genome, contains only one exon, and its 5'-upstream sequence does not have a JH response element. Although Bommo-JHDK is highly expressed in the gut of the silkworm, its mRNA expression remains at a constant level during larval development suggesting this enzyme is constitutive and not regulated by JH, at least at the transcriptional level. Recombinant Bommo-JHDK catalyzed the conversion of 10S-JH diol into JH diol phosphate, confirming its enzymatic function. Recombinant enzyme formed a dimer and had biochemical characteristics similar to other JHDKs. Bommo-JHDK, a calcium-binding protein with kinase activity, provides unique insights on how JH levels are regulated in the silkworm.

The role of nutrition in creation of the eye imaginal disc and initiation of metamorphosis in Manduca sexta

With the exception of the wing imaginal discs, the imaginal discs of Manduca sexta are not formed until early in the final larval instar. An early step in the development of these late-forming imaginal discs from the imaginal primordia appears to be an irreversible commitment to form pupal cuticle at the next molt. Similar to pupal commitment in other tissues at later stages, activation of broad expression is correlated with pupal commitment in the adult eye primordia. Feeding is required during the final larval instar for activation of broad expression in the eye primordia, and dietary sugar is the specific nutritional cue required. Dietary protein is also necessary during this time to initiate the proliferative program and growth of the eye imaginal disc. Although the hemolymph titer of juvenile hormone normally decreases to low levels early in the final larval instar, eye disc development begins even if the juvenile hormone titer is artificially maintained at high levels. Instead, creation of the late-forming imaginal discs in Manduca appears to be controlled by unidentified endocrine factors whose activation is regulated by the nutritional state of the animal.

Molecular and biochemical characterization of juvenile hormone epoxide hydrolase from the silkworm, Bombyx mori

One major route of insect juvenile hormone (JH) degradation is epoxide hydration by JH epoxide hydrolase (JHEH). A full-length cDNA (1536 bp) encoding a microsomal JHEH was isolated from the silkworm, Bombyx mori. Bommo-JHEH cDNA contains an open reading frame encoding a 461-amino acid protein (52 kDa), which reveals a high degree of similarity to the previously reported insect JHEHs. The residues Tyr298, Tyr373, and the HGWP motif corresponding to the oxyanion hole of JHEHs and the residues Asp227, His430, and Glu403 in the catalytic triad are well conserved in Bommo-JHEH. Bommo-JHEH was highly expressed in the fat body, where its mRNA expression pattern was in contrast to the pattern of hemolymph levels of JH during the larval development, suggesting that Bommo-JHEH plays an important role in JH degradation. Recombinant Bommo-JHEH (52 kDa) expressed in Sf9 insect cells was membrane-bound and had a high level of enzyme activity (300-fold over the control activity). This Bommo-JHEH study provides a better understanding of how JH levels are regulated in the domesticated silkworm.

Juvenile hormone synthesis, metabolism, and resulting haemolymph titre in Heliothis virescens larvae parasitized by Toxoneuron nigriceps

Last instar larvae of the tobacco budworm, Heliothis virescens F., fail to pupate and have little 20-hydroxyecdysone when parasitized by Toxoneuron nigriceps (Viereck). In this paper, we extend these observations to juvenile hormone (JH) to determine if parasitism by this wasp affects other endocrine systems. To this end, we compared the production of JH by corpora cardiaca-corpora allata complexes (CC-CA), the metabolism of JH by haemolymph enzymes, and the haemolymph titre of JH in parasitized and non-parasitized control larvae of H. virescens during the last larval instar. CC-CA from parasitized and control larvae had similar peaks of JH synthesis on day 1 of the fifth instar, with JH II accounting for more than 90% of total JH in both groups. On subsequent days, JH synthesis dropped to undetectable levels more quickly in non-parasitized controls than in parasitized larvae. JH metabolism by haemolymph of parasitized and control animals increased from low levels on day 1 of the fifth instar to high levels on days 2 and 3 of the instar. JH metabolism was significantly higher in control larvae than in parasitized larvae. After day 3, JH metabolism decreased in both groups, but was significantly higher in parasitized larvae. The major metabolite of JH in both groups was JH acid, though traces of JH diol and JH acid diol were also detected. The haemolymph titre of JH in both groups peaked on day 1 of the fifth instar and, similar to the synthesis of JH by CC-CA, decreased more rapidly in control larvae. As a result, non-parasitized animals had significantly lower JH titres on day 2. The higher JH titres observed in parasitized larvae during the early fifth instar may contribute to their developmental arrest. The possible role of these JH alterations in the host developmental and metabolic redirection is discussed and a more comprehensive physiological model accounting for host-parasitoid interactions is proposed.

In vitro expression and biochemical characterization of juvenile hormone esterase from Manduca sexta

Juvenile hormone esterase (JHE) is a selective enzyme that hydrolyzes the methyl ester of juvenile hormone. This enzyme plays an important role in the regulation of metamorphosis in caterpillars, and is implicated in additional roles in development and reproduction in this and other orders of insect. The full length coding region of the JHE cDNA from Manduca sexta was subcloned into the baculovirus AcMNPV genome under the control of the p10 promoter. The recombinant virus demonstrated the expression of high levels of JHE activity when infected into Hi5 cells from Trichoplusia ni. The recombinant protein was partially purified by anion exchange chromatography and its biochemical characterization showed similar features to the wild type protein. The recombinant JHE has an estimated MW of 66500 Da. Some heterogeneity with the enzyme was observed when analyzed by isoelectric focusing, although the peak of JHE activity was observed at pI=6.0. It is highly sensitive to trifluoroketone inhibitors and certain phosphoramidothiolates, while relatively insensitive to other common esterase inhibitors. Incubating the enzyme with various organic solvents and detergents showed that the enzyme is activated at lower concentrations of solvents/detergents and remains significantly active even at high concentrations. The high tolerance of organic solvents may make this JHE enzyme useful in future applications as a synthetic catalyst.

Juvenile hormone diol kinase. I. Purification, characterization, and substrate specificity of juvenile hormone-selective diol kinase from Manduca sexta

Manduca sexta juvenile hormone diol kinase (JHDK) catalyzes the conversion of juvenile hormone (JH) diol to JH diol phosphate. JHDK may be the first example of a phosphotransferase directly involved in the catabolism and inactivation of a lipid-soluble hormone. JHDK is an enzyme crucial for secondary metabolism of JH and possesses high specificity and catalytic efficiency for JH diol. In this study, the purification and characterization of native JHDK are described; its enzymatic properties are examined; and its role in cellular JH metabolism is explored. Using a variety of potential substrates, we show that JHDK has a preference for ATP, but will catalyze the formation of JH diol phosphate with GTP as the phosphate donor. JHDK has a nanomolar K(m) for JH I diol and a low micromolar value for MgATP. JH II and III diols also serve as phosphate acceptors with low micromolar K(m), whereas other diol derivatives of terpenoid esters structurally similar to JH metabolites are not phosphorylated. The reaction proceeds via a sequential Bi Bi mechanism. JHDK is active as a homodimer with a subunit molecular mass of 20 kDa. JHDK binds 5'-p-fluorosulfonylbenzoyladenosine and is inhibited by micromolar levels of Ca2+.

Effects of juvenile hormone and ecdysone on the timing of vitellogenin appearance in hemolymph of queen and worker pupae of Apis mellifera

The caste-specific regulation of vitellogenin synthesis in the honeybee represents a problem with many yet unresolved details. We carried out experiments to determine when levels of vitellogenin are first detected in hemolymph of female castes of Apis mellifera, and whether juvenile hormone and ecdysteroids modulate this process. Vitellogenin levels were measured in hemolymph using immunological techniques. We show that in both castes the appearance of vitellogenin in the hemolymph occurs during the pupal period, but the timing was different in the queen and worker. Vitellogenin appears in queens during an early phase of cuticle pigmentation approximately 60h before eclosion, while in workers the appearance of vitellogenin is more delayed, initiating in the pharate adult stage, approximately 10h before eclosion. The timing of vitellogenin appearance in both castes coincides with a slight increase in endogenous levels of juvenile hormone that occurs at the end of pupal development. The correlation between these events was corroborated by topical application of juvenile hormone. Exogenous juvenile hormone advanced the timing of vitellogenin appearance in both castes, but caste-specific differences in timing were maintained. Injection of actinomycin D prevented the response to juvenile hormone. In contrast, queen and worker pupae that were treated with ecdysone showed a delay in the appearance of vitellogenin. These data suggest that queens and workers share a common control mechanism for the timing of vitellogenin synthesis, involving an increase in juvenile hormone titers in the presence of low levels of ecdysteroids.

Endocrine insights into the evolution of metamorphosis in insects

This review explores the roles of ecdysone and juvenile hormone (JH) in the evolution of complete metamorphosis and how metamorphosis, in turn, has impacted endocrine signaling. JH is a key player in the evolution of metamorphosis because it can act on embryos from more basal insect groups to suppress morphogenesis and cause premature differentiation, functions needed for transforming the transitional pronymphal stage of hemimetabolous insects into a functional larval stage. In the ancestral condition, imaginal-related growth is then delayed until JH finally disappears during the last larval instar. In the more derived groups of the Holometabola, selective tissues have escaped this JH suppression to form early-growing imaginal discs. We discuss how complete metamorphosis may have influenced the molecular aspects of both ecdysone and JH signaling.

The modes of action of juvenile hormones: some questions we ought to ask

This paper argues that the current dogma that juvenile hormones are structurally unique and constitute a family of derivatives of farnesoic acid which are produced by the corpus allatum (CA), secreted into the hemolymph, frequently transported by binding proteins, enter cells by diffusion across the cell membrane and there the products of the CA interact in some way with the genome, probably via nuclear receptors of the steroid superfamily, may not be tenable. It does so by examining the following questions. How many JHs are there? Are there other sources of JH in insects? Are there non-farnesoids with JH activity in insects? How does JH get into cells? Is the product of the CA the effective hormone? How many modes of action are there? How many receptors are there?