The Bombyx mori sex pheromone biosynthetic pathway is not mediated by cAMP

Octopamine terminates sex pheromone biosynthesis by suppressing PBAN signal in moths

The biosynthesis and termination of insect sex pheromones should be accurately regulated. In most moths, the biosynthesis and release of sex pheromones are regulated by a class of neuropeptides known as pheromone biosynthesis activating neuropeptides (PBANs). However, endogenous mechanisms underlying the termination of sex pheromone biosynthesis in moths remain elusive. In the present study, Helicoverpa armigera was employed as a model to investigate the role of octopamine (OA) in the inhibition of sex pheromone biosynthesis. Results demonstrated that the release of sex pheromones decreased with an increase in OA titres in older female moths. Moreover, OA treatment led to a significant decrease in sex pheromone production, female capability to attract male counterparts and subsequent female acceptance, indicating its inhibitory role in sex pheromone release. Subsequent qPCR and RNAi analyses revealed that OctβR was a key receptor of OA that regulated sex pheromone biosynthesis. In addition, the OA/OctβR signal suppressed intracellular Ca²⁺ levels and attenuated PBAN-mediated increase in the enzyme activities of calcineurin and acetyl-CoA carboxylase as demonstrated by OA treatment and OctβR-RNAi. Altogether, these results revealed a mechanism underlying the inhibition of sex pheromone production by OA via suppression of PBAN signalling in moths.

Hexokinase Is Required for Sex Pheromone Biosynthesis in Helicoverpa armigera

Acetyl-CoA, the precursor of sex pheromone biosynthesis in Helicoverpa armigera, is generated from glycolysis. As the first speed-limited enzyme in glycolysis, Hexokinase (HK) plays an important role in acetyl-CoA production. However, the function of HK in sex pheromone production remains unclear. This study employed H. armigera as material to explore the role of HK in sex pheromone production. Results demonstrated that the transcription profile of HaHK in female moth pheromone glands (PGs) was consistent with the release fluctuation of sex pheromone. Interference of HaHK prevented the increase of acetyl-CoA content induced by PBAN. Therefore, knockdown of HaHK in female PGs caused significant decreases in (Z)-11-hexadecenal (Z11-16:Ald) production, female capability to attract males, and mating rate. Furthermore, sugar feeding (5% sugar) increased the transcription and enzymatic activity of HK. Pheromone biosynthesis activating neuropeptide (PBAN) signal phospho-activated HaHK in PGs and Sf9 cells via protein kinase A (PKA), as shown by pharmacological inhibitor analysis. In general, our study confirmed that PBAN/cAMP/PKA signal activated HaHK, in turn promoted glycolysis to ensure the supply of acetyl-CoA, and finally facilitated sex pheromone biosynthesis and subsequent mating behavior.

Identification and functional characterization of the pheromone biosynthesis activating neuropeptide receptor isoforms from Mamestra brassicae

In most moth species, including Mamestra brassicae, pheromone biosynthesis activating neuropeptide (PBAN) regulates pheromone production. Generally, PBAN acts directly on the pheromone gland (PG) cells via its specific G protein-coupled receptor (i.e. PBANR) with Ca²⁺ as a second messenger. In this study, we identified cDNAs encoding three variants (A, B and C) of the M. brassicae PBANR (Mambr-PBANR). The full-length coding sequences were transiently expressed in cultured Trichoplusia ni cells and Sf9 cells for functional characterization. All three isoforms dose-dependently mobilized extracellular Ca²⁺ in response to PBAN analogs with Mambr-PBANR-C exhibiting the greatest sensitivity. Fluorescent confocal microscopy imaging studies demonstrated binding of a rhodamine red-labeled ligand (RR10CPBAN) to all three Mambr-PBANR isoforms. RR10CPBAN binding did not trigger ligand-induced internalization in cells expressing PBANR-A, but did in cells expressing the PBANR-B and -C isoforms. Furthermore, activation of the PBANR-B and -C isoforms with the 18 amino acid Mambr-pheromonotropin resulted in co-localization with a Drosophila melanogaster arrestin homolog (Kurtz), whereas stimulation with an unrelated peptide had no effect. PCR-based profiling of the three transcripts revealed a basal level of expression throughout development with a dramatic increase in PG transcripts from the day of adult emergence with PBANR-C being the most abundant.

Calcineurin-mediated Dephosphorylation of Acetyl-coA Carboxylase is Required for Pheromone Biosynthesis Activating Neuropeptide (PBAN)-induced Sex Pheromone Biosynthesis in Helicoverpa armigera

Chemical signaling plays a critical role in the behavior and physiology of many animals. Female insects, as many other animals, release sex pheromones to attract males for mating. The evolutionary and ecological success of insects therefore hinges on their ability to precisely mediate (including initiation and termination) pheromone biosynthesis. Pheromone biosynthesis activating neuropeptide (PBAN) acts directly on pheromone glands to regulate sex pheromone production using Ca2+ and cyclic-AMP as secondary messengers in the majority of species. However, the molecular mechanism downstream of the secondary messengers has not yet been elucidated in heliothine species. The present study shows that calcineurin, protein kinase A (PKA) and acetyl-coA carboxylase (ACC) are key components involved in PBAN-induced sex pheromone biosynthesis in Helicoverpa armigera using PBAN-dependent phosphoproteomics in combination with transcriptomics. RNAi-mediated knockdown and inhibitor assay demonstrated that calcineurin A is required for PBAN-induced ACC activation and sex pheromone production. Calcineurin-dependent phosphoproteomics and in vitro calcineurin phosphorylation assay further revealed that calcineurin regulated ACC activity by dephosphorylating ser84 and ser92. In addition, PKA-dependent phosphoproteomics and activity analysis revealed that PKA reduces the activity of AMP-activated protein kinase (AMPK), a negative regulator of ACC by phosphorylating the conserved ser92. Taken together, our findings indicate that calcineurin acts as the downstream signal of PBAN/G-protein receptor/Ca2+ to activate ACC through dephosphorylation while inactivating AMPK via PKA to reduce ACC phosphorylation, thus facilitating calcineurin activation of ACC.

Molecular Cloning and Characterization of G Alpha Proteins from the Western Tarnished Plant Bug, Lygus hesperus

The Gα subunits of heterotrimeric G proteins play critical roles in the activation of diverse signal transduction cascades. However, the role of these genes in chemosensation remains to be fully elucidated. To initiate a comprehensive survey of signal transduction genes, we used homology-based cloning methods and transcriptome data mining to identity Gα subunits in the western tarnished plant bug (Lygus hesperus Knight). Among the nine sequences identified were single variants of the Gαi, Gαo, Gαs, and Gα12 subfamilies and five alternative splice variants of the Gαq subfamily. Sequence alignment and phylogenetic analyses of the putative L. hesperus Gα subunits support initial classifications and are consistent with established evolutionary relationships. End-point PCR-based profiling of the transcripts indicated head specific expression for LhGαq4, and largely ubiquitous expression, albeit at varying levels, for the other LhGα transcripts. All subfamilies were amplified from L. hesperus chemosensory tissues, suggesting potential roles in olfaction and/or gustation. Immunohistochemical staining of cultured insect cells transiently expressing recombinant His-tagged LhGαi, LhGαs, and LhGαq1 revealed plasma membrane targeting, suggesting the respective sequences encode functional G protein subunits.

Cloning and expression analysis of G-protein Gαq subunit and Gβ1 subunit from Bemisia tabaci Gennadius (Homoptera: Aleyrodidae)

The heterotrimeric G proteins play an essential role in a wide variety of signal transduction pathways, mediating the process of chemical signals from the environment in all higher eukaryotic organisms. In this article, two G-protein subunit genes encoding Gαq and Gβ1 were cloned from Bemisia tabaci Gennadius. The full-length cDNA sequence of BtGαq consisted of 2,336 bp with an ORF of 1,062 bp encoding 353 amino acids and BtGβ1 had a full length of 1,942 bp with an ORF of 1,023 nucleotides encoding 340 amino acids. The amino acid sequences of BtGαq and BtGβ1 from B. tabaci B biotype were identical to those from the Q biotype. Phylogenetic analysis identified G protein α and β subunit families from insects based on their amino acid sequences. The expression patterns of BtGαq and BtGβ1 at different development stages and in different body regions were analyzed by real-time quantitative PCR and Western blot. The results show that BtGαq and BtGβ1 are neither developmental stage-specific nor tissue-specific. The transcript levels of BtGαq in the B biotype are similar to that in the Q biotype, the transcript levels of BtGβ1 at egg, first instar and pupae in B biotype were significantly higher than that in Q biotype. The transcript levels of BtGαq and BtGβ1 in the head were significantly higher than those in thorax and abdomen indicating that they are involved in nervous system and sensory functions.

Identification of a diacylglycerol acyltransferase 2 gene involved in pheromone biosynthesis activating neuropeptide stimulated pheromone production in Bombyx mori

Diacylglycerol acyltransferase (DGAT) catalyzes the final step in triacylglycerol biosynthesis. In the present study, a DGAT2 gene from Bombyx mori was characterized. Temporal expression profiles indicated that BmDGAT2 steadily increased from 96 h before eclosion (-96 h) to an expression peak in the pheromone glands (PGs) of new-emerged female (0 h), a key stage for sex pheromone production. Spatial expression analysis revealed that the BmDGAT2 transcript was most richly expressed in PGs. Decapitation and subsequent methoprene, a juvenile hormone (JH) analog, treatment experiments revealed that JH had no influence on the expression of BmDGAT2 transcript before emergence, but inhibited the expression of BmDGAT2 transcript when administered to newly emerged adults. Further RNAi analysis confirmed that the decrease in BmDGAT2 mRNA level caused a significant reduction in sex pheromone production. Thus, DGAT2 is a key enzyme regulating B. mori sex pheromone synthesis and release.

Studies of sex pheromone production under neuroendocrine control by analytical and morphological means in the oriental armyworm, Pseudaletia separata, Walker (Lepidoptera: Noctuidae)

Most female moths produce species-specific sex pheromone blends in the modified epidermal pheromone gland (PG) cells generally located between the 8 and 9th abdominal segments. The biosynthesis is often regulated by pheromone biosynthesis activating neuropeptide (PBAN) either in or prior to de novo fatty acid synthesis or at the formation of oxygenated functional group. In Pseudaletia separata, information about life span, calling, PG morphology, daily fluctuation of pheromone production and its hormonal regulation is limited. We measured pheromone titer daily (16:8; L:D) at 2h intervals in scotophase. Blend ratio stabilized during the 2nd day (till 4-5th) at 6th hour of scotophase, with the ratio of 27.5:12.8:44.4:15.3 for Z-11-16OH:16OH:Z-11-16Ac:16Ac, respectively. Females showed calling behavior from this time. We found with light and fluorescence microscopy that PG consisted of intersegmental membrane (A part), and dorso-lateral region of 9th abdominal segment (B part), encountering for ∼ 35% of total production revealed by gas chromatography. Ratios did not reveal difference. We did not find precursor (triacylglycerols) accumulation in form of lipid droplets, implying that PBAN stimulates de novo biosynthesis of 16:acyl precursors. In vivoHez-PBAN injections (1-3 × 5 pmol, 2h intervals) into 3 days old 16-18 h decapitated females stimulated pheromone production, both in A and B parts. Blend analyses including ratios suggest stimulation of the initial phase of synthesis, but desaturation of fatty acyl intermediates do not follow proportionally. More saturated fatty acid is converted from the available pool to the final OH and Ac, compared to females kept intact in scotophase. In vitro studies (PGs incubated 4-6h in the presence of 0.25 or 0.5 μM Hez-PBAN, especially with surplus 2mM malonyl-CoA) revealed higher saturated component ratio than the unsaturated, compared to natural blend or in vivo injections.

Hormone signaling linked to silkmoth sex pheromone biosynthesis involves Ca2+/calmodulin-dependent protein kinase II-mediated phosphorylation of the insect PAT family protein Bombyx mori lipid storage droplet protein-1 (BmLsd1)

Species-specific sex pheromones released by female moths to attract conspecific male moths are synthesized de novo in the pheromone gland (PG) via the fatty acid biosynthetic pathway. This pathway is regulated by a neurohormone termed pheromone biosynthesis activating neuropeptide (PBAN), a 33-amino acid peptide that originates in the subesophageal ganglion. In the silkmoth, Bombyx mori, cytoplasmic lipid droplets, which store the sex pheromone (bombykol) precursor fatty acid, accumulate in PG cells. PBAN stimulates lipolysis of the stored lipid droplet triacylglycerols (TAGs) and releases the precursor for final modification. PBAN exerts its physiological function via the PG cell-surface PBAN receptor, a G protein-coupled receptor that belongs to the neuromedin U receptor family. The PBAN receptor-mediated signal is transmitted via a canonical store-operated channel activation pathway utilizing Gq-mediated phospholipase C activation (Hull, J. J., Kajigaya, R., Imai, K., and Matsumoto, S. (2007) Biosci. Biotechnol. Biochem. 71, 1993-2001; Hull, J. J., Lee, J. M., Kajigaya, R., and Matsumoto, S. (2009) J. Biol. Chem. 284, 31200-31213; Hull, J. J., Lee, J. M., and Matsumoto, S. (2010) Insect Mol. Biol. 19, 553-566). Little, however, is known about the molecular components regulating TAG lipolysis in PG cells. In the current study we found that PBAN signaling involves phosphorylation of an insect PAT family protein named B. mori lipid storage droplet protein-1 (BmLsd1) and that BmLsd1 plays an essential role in the TAG lipolysis associated with bombykol production. Unlike mammalian PAT family perilipins, however, BmLsd1 activation is dependent on phosphorylation by B. mori Ca(2+)/calmodulin-dependent protein kinase II rather than protein kinase A.

Gqalpha-linked phospholipase Cbeta1 and phospholipase Cgamma are essential components of the pheromone biosynthesis activating neuropeptide (PBAN) signal transduction cascade

Sex pheromone production for most moths is regulated by pheromone biosynthesis activating neuropeptide (PBAN). In Bombyx mori, PBAN binding triggers the opening of store-operated Ca(2+) channels, suggesting the involvement of a receptor-activated phospholipase C (PLC). In this study, we found that PLC inhibitors U73122 and compound 48/80 reduced sex pheromone production and that intracellular levels of (3)H-inositol phosphate species increased following PBAN stimulation. In addition, we amplified cDNAs from pheromone glands corresponding to PLCbeta1, PLCbeta4, PLCgamma and two G protein alpha subunits, Go and Gq. In vivo RNA interference-mediated knockdown analyses revealed that BmPLCbeta1, BmGq1, and unexpectedly, BmPLCgamma, are part of the PBAN signal transduction cascade.

Unraveling the pheromone biosynthesis activating neuropeptide (PBAN) signal transduction cascade that regulates sex pheromone production in moths

Studies over the past three decades have demonstrated that female moths usually produce sex pheromones as multicomponent blends in which the ratios of the individual components are precisely controlled, making it possible to generate species-specific pheromone blends. Most moth pheromone components are de novo synthesized from acetyl-CoA in the pheromone gland (PG) through modifications of fatty acid biosynthetic pathways. Pheromone biosynthesis activating neuropeptide (PBAN), a neurohormone produced by a cephalic organ (subesophageal ganglion) stimulates sex pheromone biosynthesis in the PG via an influx of extracellular Ca(2+). In recent years, we have expanded our knowledge of the precise mechanisms underlying silkmoth (Bombyx mori) sex pheromone production by characterizing a number of key molecules. In this review, we want to highlight our efforts in elucidating these mechanisms in B. mori and to understand how they relate more broadly to lepidopteran sex pheromone production in general.

Pheromone biosynthesis activating neuropeptide (PBAN): regulatory role and mode of action

This review focuses on the endocrine regulation of reproductive behavior in moth species with particular emphasis on Helicoverpa spp. Reproductive behavior in most adult moths is dependent on the release of a unique blend of sex pheromones by the females to attract conspecific males. Mating, on the other hand, results in a loss of sexual receptivity due to the transfer of secretions from the male accessory glands, which renders females unattractive to ensuing mates. Synchronization of sexual behavior is attained by the timely release of Pheromone-Biosynthesis-Activating Neuropeptide (PBAN), a member of the PBAN/Pyrokinin neuropeptide family, characterized by a common amino acid sequence FXPRLamide motif in the C-terminus. PBAN is released into the hemolymph of females during the scotophase and is drastically reduced after mating, contributing to the loss in female receptivity. Pheromone production is age-dependent and Juvenile Hormone is involved in its regulation. PBAN activates pheromone production through its binding to a PBAN-Receptor (PBAN-R) and subsequent up-regulation of key enzymes in the biosynthetic pathway. The PBAN-R gene was identified as a member of the G-protein coupled receptor family (GPCRs), classified with the vertebrate subfamily of neuromedin U receptors. Using both biochemical and in silico mutagenesis studies, putative binding sites are predicted. Differential expression studies reveal its localization in pheromone glands, neural tissues and the male aedeagus. In the latter tissue, no activity and/or receptor-binding can be detected in response to PBAN. These results raise many questions concerning the evolutionary role of the PBAN/Pyrokinin receptors belonging to the GPCR family.

Molecular mechanisms underlying sex pheromone production in the silkmoth, Bombyx mori: characterization of the molecular components involved in bombykol biosynthesis

Many species of female moths produce sex pheromones to attract conspecific males. To date, sex pheromones from more than 570 moth species have been chemically identified. Most moth species utilize Type I pheromones that consist of straight-chain compounds 10-18 carbons in length with a functional group of a primary alcohol, aldehyde, or acetate ester and usually with several double bonds. In contrast, some moth species use unsaturated hydrocarbons or hydrocarbon epoxides, classified as Type II lepidopteran pheromones, as sex pheromones. Studies over the past three decades have demonstrated that female moths usually produce sex pheromones as multi-component blends where the ratio of the individual components is precisely controlled, thus making it possible to generate species-specific pheromone blends. As for the biosynthesis of Type I pheromones, it is well established that they are de novo synthesized in the pheromone gland (PG) through modifications of fatty acid biosynthetic pathways. However, as many of the molecular components within the PG cells (i.e., enzymes, proteins, and small regulatory molecules) have not been functionally characterized, the molecular mechanisms underlying sex pheromone production in PG cells remain poorly understood. To address this, we have recently characterized some of the molecules involved in the biosynthesis of the sex pheromone bombykol in the silkmoth, Bombyx mori. Characterization of these, and other, key molecules will facilitate our understanding of the precise mechanisms underlying lepidopteran sex pheromone production.