Molecular characterization of the gene encoding the precursor protein of diapause hormone and pheromone biosynthesis activating neuropeptide (DH-PBAN) of the silkworm, Bombyx mori and its distribution in some insects

Endocrine Control of Lipid Metabolism

Lipids are essential in insects and play pleiotropic roles in energy storage, serving as a fuel for energy-driven processes such as reproduction, growth, development, locomotion, flight, starvation response, and diapause induction, maintenance, and termination. Lipids also play fundamental roles in signal transduction, hormone synthesis, forming components of the cell membrane, and thus are essential for maintenance of normal life functions. In insects, the neuroendocrine system serves as a master regulator of most life activities, including growth and development. It is thus important to pay particular attention to the regulation of lipid metabolism through the endocrine system, especially when considering the involvement of peptide hormones in the processes of lipogenesis and lipolysis. In insects, there are several lipogenic and lipolytic hormones that are involved in lipid metabolism such as insulin-like peptides (ILPs), adipokinetic hormone (AKH), 20-hydroxyecdysone (20-HE), juvenile hormone (JH), and serotonin. Other neuropeptides such as diapause hormone-pheromone biosynthesis activating neuropeptide (DH-PBAN), CCHamide-2, short neuropeptide F, and the cytokines Unpaired 1 and 2 may play a role in inducing lipogenesis. On the other hand, neuropeptides such as neuropeptide F, allatostatin-A, corazonin, leukokinin, tachykinins, limostatins, and insulin-like growth factor (ILP6) stimulate lipolysis. This chapter briefly discusses the current knowledge of the endocrine regulation of lipid metabolism in insects that could be utilized to reveal differences between insects and mammalian lipid metabolism which may help understand human diseases associated with dysregulation of lipid metabolism. Physiological similarities of insects to mammals make them valuable model systems for studying human diseases characterized by disrupted lipid metabolism, including conditions like diabetes, obesity, arteriosclerosis, and various metabolic syndromes.

Lipopolysaccharide-Induced Immunological Tolerance in Monocyte-Derived Dendritic Cells

Bacterial lipopolysaccharides (LPS), also referred to as endotoxins, are major outer surface membrane components present on almost all Gram-negative bacteria and are major determinants of sepsis-related clinical complications including septic shock. LPS acts as a strong stimulator of innate or natural immunity in a wide variety of eukaryotic species ranging from insects to humans including specific effects on the adaptive immune system. However, following immune stimulation, lipopolysaccharide can induce tolerance which is an essential immune-homeostatic response that prevents overactivation of the inflammatory response. The tolerance induced by LPS is a state of reduced immune responsiveness due to persistent and repeated challenges, resulting in decreased expression of pro-inflammatory modulators and up-regulation of antimicrobials and other mediators that promote a reduction of inflammation. The presence of environmental-derived LPS may play a key role in decreasing autoimmune diseases and gut tolerance to the plethora of ingested antigens. The use of LPS may be an important immune adjuvant as demonstrated by the promotion of IDO1 increase when present in the fusion protein complex of CTB-INS (a chimera of the cholera toxin B subunit linked to proinsulin) that inhibits human monocyte-derived DC (moDC) activation, which may act through an IDO1-dependent pathway. The resultant state of DC tolerance can be further enhanced by the presence of residual E. coli lipopolysaccharide (LPS) which is almost always present in partially purified CTB-INS preparations. The approach to using an adjuvant with an autoantigen in immunotherapy promises effective treatment for devastating tissue-specific autoimmune diseases like multiple sclerosis (MS) and type 1 diabetes (T1D).

Molecular and Functional Characterization of Pyrokinin-Like Peptides in the Western Tarnished Plant Bug Lygus hesperus (Hemiptera: Miridae)

Simple Summary

Neuropeptides regulate most insect biological functions. One such group of peptides, the pyrokinins (PKs), are distinguished by a C-terminal FXPRLamide. While widely distributed in most insects, they are poorly characterized in plant bugs. To address this limitation, we identified the PK transcript in the western tarnished plant bug (Lygus hesperus) and examined its expression. The Lygus PK transcript is predicted to yield three PK-like peptides but only two (LyghePKa and LyghePKb) have the characteristic C-terminal amide. The transcript is expressed throughout development and is most abundant in heads. A custom FXPRLamide antibody revealed immunoreactive cells throughout the Lygus central nervous system consistent with typical neuropeptide expression. To assess potential functional roles of the peptides, a fluorescence-based Ca²⁺ influx assay using cultured insect cells stably expressing a moth PK receptor was performed. LyghePKa was unable to stimulate receptor activation, whereas LyghePKb triggered a robust response. The in vivo pheromonotropic activity of the two peptides was likewise assessed using three different moth species. Like the cell culture system, only the LyghePKb peptide was active. The study suggests evolutionary divergence of the PK gene in plant bugs and provides critical insights into likely biological functions in the western tarnished plant bug.

Abstract

The pyrokinin (PK) family of insect neuropeptides, characterized by C termini consisting of either WFGPRLamide (i.e., PK1) or FXPRLamide (i.e., PK2), are encoded on the capa and pk genes. Although implicated in diverse biological functions, characterization of PKs in hemipteran pests has been largely limited to genomic, transcriptomic, and/or peptidomic datasets. The Lygus hesperus (western tarnished plant bug) PK transcript encodes a prepropeptide predicted to yield three PK2 FXPRLamide-like peptides with C-terminal sequences characterized by FQPRSamide (LyghePKa), FAPRLamide (LyghePKb), and a non-amidated YSPRF. The transcript is expressed throughout L. hesperus development with greatest abundance in adult heads. PRXamide-like immunoreactivity, which recognizes both pk- and capa-derived peptides, is localized to cells in the cerebral ganglia, gnathal ganglia/suboesophageal ganglion, thoracic ganglia, and abdominal ganglia. Immunoreactivity in the abdominal ganglia is largely consistent with capa-derived peptide expression, whereas the atypical fourth pair of immunoreactive cells may reflect pk-based expression. In vitro activation of a PK receptor heterologously expressed in cultured insect cells was only observed in response to LyghePKb, while no effects were observed with LyghePKa. Similarly, in vivo pheromonotropic effects were only observed following LyghePKb injections. Comparison of PK2 prepropeptides from multiple hemipterans suggests mirid-specific diversification of the pk gene.

Hormonal Regulation of Diapause and Development in Nematodes, Insects, and Fishes

Diapause is a state of developmental arrest adopted in response to or in anticipation of environmental conditions that are unfavorable for growth. In many cases, diapause is facultative, such that animals may undergo either a diapause or a non-diapause developmental trajectory, depending on environmental cues. Diapause is characterized by enhanced stress resistance, reduced metabolism, and increased longevity. The ability to postpone reproduction until suitable conditions are found is important to the survival of many animals, and both vertebrate and invertebrate species can undergo diapause. The decision to enter diapause occurs at the level of the whole animal, and thus hormonal signaling pathways are common regulators of the diapause decision. Unlike other types of developmental arrest, diapause is programmed, such that the diapause developmental trajectory includes a pre-diapause preparatory phase, diapause itself, recovery from diapause, and post-diapause development. Therefore, developmental pathways are profoundly affected by diapause. Here, I review two conserved hormonal pathways, insulin/IGF signaling (IIS) and nuclear hormone receptor signaling (NHR), and their role in regulating diapause across three animal phyla. Specifically, the species reviewed are Austrofundulus limnaeus and Nothobranchius furzeri annual killifishes, Caenorhabditis elegans nematodes, and insect species including Drosophila melanogaster, Culex pipiens, and Bombyx mori. In addition, the developmental changes that occur as a result of diapause are discussed, with a focus on how IIS and NHR pathways interact with core developmental pathways in C. elegans larvae that undergo diapause.

Changes in expressions of ecdysteroidogenic enzyme and ecdysteroid signaling genes in relation to Bombyx embryonic development

Although the role of ecdysteroids in regulating egg diapause process in Bombyx mori is well documented, temporal changes in expression levels of genes involved in ecdysteroid biosynthesis and its downstream signaling are less well understood. In the present study, we studied changes in expression levels of genes involved in ecdysteroid biosynthesis and its downstream signaling during embryonic development of B. mori. Results showed that in diapause eggs, the expression of ecdysteroid-phosphate phosphatase (EPPase) gene and Halloween genes (Spook [Spo] and Shade [Shd]) remained at very low levels. However, in eggs whose diapause initiation was prevented by HCl, significant increases in the messenger RNA (mRNA) levels of EPPase, Spo, and Shd were detected during embryonic development. Other Halloween genes (Neverland [Nvd] and Phantom [Phm]) also showed different changes between diapause and HCl-treated eggs. However, genes of Disembodied (Dib) and Shadow (Sad) showed similar changes in both diapause and HCl-treated eggs. We further investigated changes in expression levels of ecdysone receptor genes (EcRA, EcRB1, and USP) and downstream signaling genes (E75A, E75B, E74A, E74B, Br-C, HR3, HR4, KR-H1, and FTZ-F1). Results showed that genes of EcRA and the other nuclear receptors (E75A, E75B, E74A, HR3, HR4, KR-H1, and FTZ-F1) exhibited significant differential patterns between diapause and HCl-treated eggs, with increased levels being detected during later stages of embryonic development in HCl-treated eggs. Differential temporal changes in expressions of genes involved ecdysteroid biosynthesis and its downstream signaling found between diapause and HCl-treated eggs were further confirmed using nondiapause eggs. Our results showed that nondiapause eggs exhibited the same changing patterns as those in HCl-treated eggs, thus clearly indicating potential correlations between expressions of these genes and embryonic development in B. mori. To our knowledge, this is the first comprehensive report to study the transcriptional regulation of ecdysteroidogenic and ecdysteroid signaling genes, thus providing useful information for a clearer understanding of insect egg diapause mechanisms.

Distribution of Pheromone Biosynthesis-Activating Neuropeptide in the Central Nervous System of Plutella xylostella (Lepidoptera: Plutellidae)

Insect neuropeptides in the pyrokinin/pheromone biosynthesis-activating neuropeptide (PBAN) family are actively involved in many essential endocrinal functions and serve as potential targets in the search for novel insect control agents. Here, we dissect the nervous system of larval, pupal, and adult Plutella xylostella (L.) (Lepidoptera: Plutellidae) and describe the ganglion morphology and localization of PBAN during different insect developmental stages. Our results show that the central nervous system (CNS) of this species consists of four types of ganglia: cerebral ganglia (brain), subesophageal ganglion (SEG), thoracic ganglia, and abdominal ganglia. A two-lobed brain is connected to the reniform SEG with a nerve cord in larvae and prepupae, whereas in the late pupae and adults, the brain and SEG are fused, forming a brain-SEG complex. The larvae and prepupae have eight abdominal ganglia each, whereas the late pupae and adults each have four abdominal ganglia. Furthermore, all life stages of P. xylostella had similar patterns of PBAN immunoreactivity in the CNS, and the accumulation of PBAN was similar during all life stages except in adult males. PBAN immunoreactive signals were observed in the brain and SEG, and fluorescence signals originating in the SEG extended the entire length of the ventral nerve cord, ending in the terminal abdominal ganglia. Our results provide morphological data that inform the development and evolution of the CNS. In addition, they indicate that the nervous system contains PBAN, which could be used to control P. xylostella populations.

Novel Lom-dh Genes Play Potential Role in Promoting Egg Diapause of Locusta migratoria L

Diapause hormone (DH) neuropeptides in insects are produced by the genes belonging to pban/capa family. Previous studies show that DH contains a conserved sequence of WFGPRXa that plays vital role in diapause regulation of some Lepidopteran species. However, the function of DH in other species is still unknown. In order to expand our understanding of DH function in diapause induction, Lom-pban, Lom-capa, and five candidates DH precursor genes (Lom-dh1, Lom-dh2, Lom-dh3, Lom-dh4, Lom-dh5) of Locusta migratoria L. were subsequently cloned. We identified Lom-dh1 to Lom-dh5 as novel genes that encoded five types (type I–V) of 44 tandem repeats of DH-like neuropeptides, which might promote egg diapause of L. migratoria. To test this hypothesis, we identified four types of eight new neuropeptides encoded by Lom-dh using liquid chromatography–tandem mass spectrometry from the central neuron system of L. migratoria under both short (10:14 L:D) and long (16:8 L:D) photoperiods. Later on, we synthesized four type I DH-like neuropeptides, LDH1, SDH1, LDH2, and SDH2, encoded by Lom-dh2/Lom-dh3 and injected them into fifth instar female locusts. Egg diapause incidences were observed after female oviposition. The four DH-like neuropeptides significantly increased the incidence of egg diapause under the short photoperiod, but the response was absent under the long photoperiod. Injection of dsLom-dh into female adults of L. migratoria under the short photoperiod could inhibit egg diapause, with no response under the long photoperiod. This study identified a new member of pban/capa family being the second example beside Bombyx mori, where the DH showed significant role on maternal induction of diapause.

Sex-specific spatial and temporal gene expressions of Pheromone biosynthesis activating neuropeptide (PBAN) and binding proteins (PBP/OBP) in Spoladea recurvalis

Spoladea recurvalis is one of the most destructive insect pests of amaranth, a leafy vegetable in both Asia and Africa. The present study characterized the pheromone biosynthesis-activating neuropeptide (DH-PBAN) and pheromone/odorant binding proteins in S. recurvalis. The open reading frame of 600 base pairs encodes a 200-amino acid protein possessing five neuropeptide motifs (DH, PBAN, α-, β-, and γ- subesophageal ganglion neuropeptides) and shares a characteristic conserved C-terminal pentapeptide fragment FXPRL. The full-length genome of Spre-DH-PBAN was 4,295 bp in length and comprised of six exons interspersed by five introns. Sequence homology and phylogenetic analysis of Spre-DH-PBAN have high similarity to its homologs in Crambidae of Lepidopteran order. We quantitatively measured the relative expression level (qRT_PCR) of Spre-DH-PBAN gene, the binding proteins such as odorant binding proteins (OBPs) and pheromone binding protein (PBPs) at different developmental stages. The results confirmed their role in recognition and chemoreception of sex pheromone components, and they were distinct, tissue- and sex-specific. This is the first report on the molecular analysis of PBAN gene and binding proteins, which can improve the understanding of molecular mechanisms of growth, development, and reproductive behavior of S. recurvalis, and may become effective targets for controlling this insect.

Effects of transgenic overexpression of diapause hormone and diapause hormone receptor genes on non-diapause silkworm

Diapause is a state of developmental arrest that is most often observed in arthropods, especially insects. The domesticated silkworm, Bombyx mori, is a typical insect that enters diapause at an early embryonic stage. Previous studies have revealed that the diapause hormone (DH) signaling molecules, especially the core members DH and DH receptor 1 (DHR1), are crucial for the determination of embryonic diapause in diapause silkworm strains. However, whether they function in non-diapause silkworm strains remains largely unknown. Here, we generated two transgenic lines overexpressing DH or DHR1 genes in a non-diapause silkworm strain, Nistari. Our results showed that developmental expression patterns of DH and DHR1 are quite similar in transgenic silkworms: both genes are highly expressed in the mid to late stages of pupae and are most highly expressed in day-6 pupae but are expressed at very low levels in other developmental stages. Moreover, the overexpression of DH or DHR1 can affect the expression of diapause-related genes but is not sufficient to induce embryonic diapause in their offspring. This study provides new insights into the function of DH and DHR1 in a non-diapause silkworm strain.

Injury-induced rapid activation of MAPK signaling in dechorionated eggs and larvae of the silkworm Bombyx mori

Previous study showed that diapause in Bombyx mori eggs can be terminated by dechorionation and that activation in the mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) in dechorionated cultured eggs is involved in diapause termination. In the present study, the possible mechanism underlying activation of ERK upon dechorionation was further investigated. Results showed that mechanical injury of diapause eggs without medium incubation also resulted in rapid increase in the phospho-ERK levels and that injury increased the phospho-ERK levels at different stages of both diapause eggs and eggs in which diapause initiation was prevented by HCl. Effects of anaerobiosis on dechorionation-stimulated phospho-ERK levels showed that the mechanical injury itself but not the dramatic increase in oxygen uptake upon injury is involved in a rapid activation of ERK. Chemical anaerobiosis on dechorionation-stimulated phospho-ERK levels and the in vivo effect of anaerobiosis showed that the supply of oxygen also plays a role in ERK signaling. In addition, injury induced the phosphorylation of c-jun N-terminal kinases (JNKs) and p38 kinase, components of two parallel MAPK pathways. A kinase assay showed a dramatic increase in JNK kinase activity in egg lysates upon injury. When newly hatched first instar larvae were injured, an increase in the phospho-ERK levels similar to that in dechorionated eggs was observed. From the results, we hypothesize that the injury-induced rapid activation of MAPK signaling, which serves as a natural signal for embryonic development, is related to diapause termination in dechorionated eggs.

Identification and expression profiling of pheromone biosynthesis activating neuropeptide in Chlumetia transversa (Walker)

Insect neuropeptides (NPs) in the pyrokinin/pheromone biosynthesis-activating neuropeptide (PBAN) family are actively involved in many essential endocrine functions. These peptides are potential targets in the search for novel insect control agents. This is the first report on the cloning and sequence determination of Chlumetia transversa (Walker) PBAN (Ct-PBAN) using rapid amplification of cDNA ends. The open reading frame of Ct-PBAN was 588bp in length and encoded 195 amino acids, which were assembled into five putative neuropeptides (diapause hormone homolog, α-neuropeptide, β-neuropeptide, PBAN, and γ-neuropeptide). These peptides were amidated at C-terminus and shared the conserved pentapeptide motif FXPR (or K) L. Moreover, Ct-PBAN had high homology to PBANs in Helicoverpa zea (84.1%), Helicoverpa armigera (83.5%), Helicoverpa assulta (83%), and Heliothis virescens (82.6%). Phylogenetic analysis showed that Ct-PBAN was closely related to its orthologs in the family Noctuidae. In addition, real-time quantitative polymerase chain reaction assays showed that the expression of Ct-PBAN peaked in the female head and was also detected at high levels in 1-d-old adults. These results suggested that Ct-PBAN is associated with sex pheromone biosynthesis in female C. transversa and could be used for developing C. transversa control systems based on molecular techniques.

Identification and expression of a new member of the pyrokinin/pban gene family in the sand fly Phlebotomus papatasi

The major family of neuropeptides (NPs) derived from the pk (pyrokinin)/pban (pheromone biosynthesis activating neuropeptide) gene are defined by a common FXPRL-NH2 or similar sequence at the C-termini. This family of peptides has been found in all insect groups investigated to date and is implicated in regulating various physiological functions, including pheromone biosynthesis and diapause, but other functions are still largely unknown in specific life stages. Here we identify two isoforms of pk/pban cDNA encoding the PBAN domain from the sand fly Phlebotomus papatasi. The two pk/pban isoforms have the same sequence except for a 63 nucleotide difference between the long and short forms, and contain no alternative mRNA splicing site. Two NP homologues, DASGDNGSDSQRTRPPFAPRLamide and SLPFSPRLamide are expected, however, sequence corresponding to the diapause hormone was not found in the P. papatasi pk/pban gene. The PBAN-like amino acid sequence homologue SNKYMTPRL is conserved in the gene, but there is no cleavage site for processing a functional peptide. Characterizing the expression of the isoforms in developmental stages and adults indicates that the short form is differentially transcribed depending on the life stage. The P. papatasi pk/pban gene is the only known pk/pban gene with two transcriptional isoforms and from examination of endoproteolytic cleavage sites is expected to produce fewer peptides than most of the pk/pban genes elucidated to date; only Drosophila melanogaster is simpler with a single NP detected by mass spectroscopy. A phylogenetic analysis showed P. papatasi pk/pban grouped more closely with other nematoceran flies rather than higher flies.

Identification and expression analysis of diapause hormone and pheromone biosynthesis activating neuropeptide (DH-PBAN) in the legume pod borer, Maruca vitrata Fabricius

Neuropeptides play essential roles in a variety of physiological responses that contribute to the development and reproduction of insects. Both the diapause hormone (DH) and pheromone biosynthesis activating neuropeptide (PBAN) belong to the PBAN/pyrokinin neuropeptide family, which has a conserved pentapeptide motif FXPRL at the C-terminus. We identified the full-length cDNA encoding DH-PBAN in Maruca vitrata, a major lepidopteran pest of leguminous crops. The open reading frame of Marvi-DH-PBAN is 591 bp in length, encoding 197 amino acids, from which five putative neuropeptides [DH, PBAN, α-subesophageal ganglion neuropeptide (SGNP), β-SGNP and γ-SGNP] are derived. Marvi-DH-PBAN was highly similar (83%) to DH-PBAN of Omphisa fuscidentalis (Lepidoptera: Crambidae), but possesses a unique C-terminal FNPRL motif, where asparagine has replaced a serine residue present in other lepidopteran PBAN peptides. The genomic DNA sequence of Marvi-DH-PBAN is 6,231 bp in size and is composed of six exons. Phylogenetic analysis has revealed that the Marvi-DH-PBAN protein sequence is closest to its homolog in Crambidae, but distant from Diptera, Coleoptera and Hymenoptera DH-PBAN, which agrees with the current taxonomy. DH-PBAN transcripts were present in the head and thoracic complex, but absent in the abdomen of M. vitrata. Real-time quantitative PCR assays have demonstrated a relatively higher expression of Marvi-DH-PBAN mRNA in the latter half of the pupal stages and in adults. These findings represent a significant step forward in our understanding of the DH-PBAN gene architecture and phylogeny, and raise the possibility of using Marvi-DH-PBAN to manage M. vitrata populations through molecular techniques.

Shotgun proteomic analysis on the diapause and non-diapause eggs of domesticated silkworm Bombyx mori

To clarify the molecular mechanisms of silkworm diapause, it is necessary to investigate the molecular basis at protein level. Here, the spectra of peptides digested from silkworm diapause and non-diapause eggs were obtained from liquid chromatography tandem mass spectrometry (LC-MS/MS) and were analyzed by bioinformatics methods. A total of 501 and 562 proteins were identified from the diapause and non-diapause eggs respectively, of which 309 proteins were shared commonly. Among these common-expressed proteins, three main storage proteins (vitellogenin precursor, egg-specific protein and low molecular lipoprotein 30 K precursor), nine heat shock proteins (HSP19.9, 20.1, 20.4, 20.8, 21.4, 23.7, 70, 90-kDa heat shock protein and heat shock cognate protein), 37 metabolic enzymes, 22 ribosomal proteins were identified. There were 192 and 253 unique proteins identified in the diapause and non-diapause eggs respectively, of which 24 and 48 had functional annotations, these unique proteins indicated that the metabolism, translation of the mRNA and synthesis of proteins were potentially more highly represented in the non-dipause eggs than that in the diapause eggs. The relative mRNA levels of four identified proteins in the two kinds of eggs were also compared using quantitative reverse transcription PCR (qRT-PCR) and showed some inconsistencies with protein expression. GO signatures of 486 out of the 502 and 545 out of the 562 proteins identified in the diapause and non-diapause eggs respectively were available. In addition, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed the Metabolism, Translation and Transcription pathway were potentially more active in the non-dipause eggs at this stage.

Diapause: delaying the developmental clock in response to a changing environment

Seasonal changes can induce organisms to modify their developmental growth. Many holometabolous insects, especially Lepidoptera, trigger diapause, an "actively induced" dormancy, for overwintering. Diapause is an alternative developmental pathway that reversibly blocks developmental growth during specific transitions and enhances the hibernating potential of the organism. Changes in environmental cues, such as light and temperature, trigger modifications in the levels, or in the timing, of developmental hormones. These in turn switch the developmental trajectory (diapause or direct development), strongly altering larval/pupal growth and inducing the appearance of diapause-bound seasonal morphs (polyphenism). We also discuss an example of vertebrate diapause using the killifish embryo as an example where diapause is an environmentally determined developmental switch analogous to that observed in lepidopteran dormancy. Based on the examples discussed here, we propose that the complex physiological responses leading to diapause might evolve quickly by relatively limited genetic changes in the regulation of hormonal signals that program normal developmental transitions.

A de novo transcriptome of the Asian tiger mosquito, Aedes albopictus, to identify candidate transcripts for diapause preparation

Background

Many temperate insects survive the harsh conditions of winter by undergoing photoperiodic diapause, a pre-programmed developmental arrest initiated by short day lengths. Despite the well-established ecological significance of photoperiodic diapause, the molecular basis of this crucial adaptation remains largely unresolved. The Asian tiger mosquito, Aedes albopictus (Skuse), represents an outstanding emerging model to investigate the molecular basis of photoperiodic diapause in a well-defined ecological and evolutionary context. Ae. albopictus is a medically significant vector and is currently considered the most invasive mosquito in the world. Traits related to diapause appear to be important factors contributing to the rapid spread of this mosquito. To generate novel sequence information for this species, as well as to discover transcripts involved in diapause preparation, we sequenced the transcriptome of Ae. albopictus oocytes destined to become diapausing or non-diapausing pharate larvae.

Results

454 GS-FLX transcriptome sequencing yielded >1.1 million quality-filtered reads, which we assembled into 69,474 contigs (N50 = 1,009 bp). Our contig filtering approach, where we took advantage of strong sequence similarity to the fully sequenced genome of Aedes aegypti, as well as other reference organisms, resulted in 11,561 high-quality, conservative ESTs. Differential expression estimates based on normalized read counts revealed 57 genes with higher expression, and 257 with lower expression under diapause-inducing conditions. Analysis of expression by qPCR for 47 of these genes indicated a high correlation of expression levels between 454 sequence data and qPCR, but congruence of statistically significant differential expression was low. Seven genes identified as differentially expressed based on qPCR have putative functions that are consistent with the insect diapause syndrome; three genes have unknown function and represent novel candidates for the transcriptional basis of diapause.

Conclusions

Our transcriptome database provides a rich resource for the comparative genomics and functional genetics of Ae. albopictus, an invasive and medically important mosquito. Additionally, the identification of differentially expressed transcripts related to diapause enriches the limited knowledge base for the molecular basis of insect diapause, in particular for the preparatory stage. Finally, our analysis illustrates a useful approach that draws from a closely related reference genome to generate high-confidence ESTs in a non-model organism.

Transcription factor fork head regulates the promoter of diapause hormone gene in the cotton bollworm, Helicoverpa armigera, and the modification of SUMOylation

The transcription factor fork head (FoxA) plays important roles in development and metabolism. Here, we cloned a fork head gene in Helicoverpa armigera, and found that the fork head protein is mainly located in the nucleus. This fork head gene belongs to the FoxA subfamily of the Fox transcription factors. The diapause hormone and pheromone biosynthesis-activating neuropeptide (DH-PBAN), which are two well-documented insect neuropeptides that regulate insect development and pheromone biosynthesis, are encoded by a single mRNA. In the present study, fork head was shown to bind strongly to the promoter of H. armigera DH-PBAN gene, and regulate its promoter activity. Furthermore, the effect of SUMOylation of the FH protein on the regulation of Har-DH-PBAN gene was investigated, and we show that the SUMO can modify Har-FH protein and cause down-regulation of DH-PBAN gene expression. These results suggest that SUMOylated FH plays a key role in insect diapause in H. armigera.

Involvement of 4E-BP phosphorylation in embryonic development of the silkworm, Bombyx mori

Phosphorylation of the translational repressor 4E-binding protein (4E-BP) plays a critical role in regulating the overall translation levels in cells. In the present study, we investigated 4E-BP phosphorylation of Bombyx mori eggs by an immunoblot analysis of a conserved phospho-specific antibody to 4E-BP and demonstrated its role during embryonic development. When HCl treatment was applied to diapause-destined eggs at 20 h after oviposition, a dramatic increase in the phosphorylation of 4E-BP occurred 5 min after treatment with HCl, and high phosphorylation levels were maintained throughout embryonic stage in HCl-treated eggs compared to those in diapause (control) eggs. When HCl treatment was applied to diapause eggs on day 10 after oviposition, no dramatic activation in 4E-BP phosphorylation occurred, indicating stage-specific effects of HCl treatment. In both non-diapause eggs and eggs whose diapause had been terminated by chilling of diapausing eggs at 5°C for 70 days and then were transferred to 25°C, high phosphorylation levels of 4E-BP were also detected. Moreover, 4E-BP phosphorylation dramatically increased when dechorionated eggs were incubated in medium. The addition of rapamycin, a specific inhibitor of mammalian target of rapamycin (TOR) signaling, and LY294002, a phosphoinositide 3-kinase (PI3K) inhibitor, but not the mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) kinase (MEK) inhibitor, U0126, dose-dependently inhibited 4E-BP phosphorylation in dechorionated eggs, indicating that PI3K/TOR signaling is an upstream signaling event involved in 4E-BP phosphorylation. Examination of 4E-BP gene expression levels showed no differences between treatments with HCl and water in the first hour after treatment, indicating that changes in phosphorylation of 4E-BP upon HCl treatment are mainly regulated at the post-transcriptional level. In addition, MAPK pathways and glycogen synthase kinase (GSK)-3β phosphorylation were not significantly affected in the first hour after HCl treatment. These results demonstrate that the rapid phosphorylation of 4E-BP is an early signaling event in embryonic development in the eggs whose diapause initiation was prevented by HCl treatment, thus being involved in the embryonic development of B. mori.

PBAN gene architecture and expression in the fire ant, solenopsis invicta

The PBAN/pyrokinin peptides are a major neuropeptide family characterized by a common FXPRLamide at the C-termini. These peptides are distributed ubiquitously in the Insecta and are involved in many essential endocrine functions, e.g. pheromone production. We report the gene architecture of the fire ant Solenopsis invicta PBAN (Soi-PBAN) gene, including the exon and intron boundaries. Furthermore, we quantified expression of the Soi-PBAN mRNA in the head, thorax and abdomen of the fire ant. The Soi-PBAN gene is comprised three exons and two introns, all composed of 13,358 nucleotides, which is 2-4 times larger than lepidopteran PBAN genes. The overall pattern of the PBAN immunoreactive neuron number and localization was similar for female and male alates, inseminated female delates, workers and queens. The Soi-PBAN mRNA expression level was highest in the head, followed by the thorax, and abdomen of adult ants. Expression in the abdominal tissues was expected to be similar to the head, or at least higher than thorax because strong PBAN immunoreactive neurons were detected previously in brain-subesophageal and abdominal ganglia. This result suggests that another FXPRL gene could be dominant in the abdomen rather than Soi-PBAN gene.

Identification of an E-box DNA binding protein, activated protein 4, and its function in regulating the expression of the gene encoding diapause hormone and pheromone biosynthesis-activating neuropeptide in Helicoverpa armigera

Activated protein 4 (AP-4), an E-box DNA-binding protein, was cloned from the cotton bollworm, Helicoverpa armigera (Har). The expression of Har-AP-4 mRNA and the protein that it encodes are significantly higher in nondiapause pupae than in diapause pupae. In vitro-translated Har-AP-4 can bind specifically to the E-box motif on the promoter of the diapause hormone and pheromone biosynthesis-activating neuropeptide (DH-PBAN). Har-AP-4, fused with the green fluorescent protein (GFP), is localized to the nucleus, and overexpression of Har-AP-4 can significantly activate the promoter of the DH-PBAN gene that is involved in nondiapause pupal development in H. armigera. These results suggest that Har-AP-4, which binds to the promoter of DH-PBAN, may play a role in regulating pupal development in H. armigera.

Embryonic diapause highlighted by differential expression of mRNAs for ecdysteroidogenesis, transcription and lipid sparing in the cricket Allonemobius socius

Embryos of the ground cricket, Allonemobius socius, enter diapause 4-5 days post-oviposition and overwinter in this dormant state that is characterized by developmental arrest. Suppressive subtractive hybridization and quantitative real-time PCR reveal eight candidate genes in pre-diapause embryos that show promise as regulators of diapause entry, when compared with embryos not destined for diapause. Identifications are based both on the magnitude/consistency of differential mRNA abundances and the predicted functions of their products when placed in context of the physiological and biochemical events of diapause characterized in our companion paper. The proteins CYP450, AKR and RACK1 (associated with ecdysteroid synthesis and signaling) are consistently upregulated in pre-diapause, followed by major downregulation later in diapause. The pattern suggests that elevated ecdysone may facilitate onset of diapause in A. socius. Upregulation seen for the transcription factors Reptin and TFDp2 may serve to depress transcription and cell cycle progression. Cathpesin B-like protease, ACLY and MSP are three downregulated genes associated with yolk mobilization and/or metabolism that we predict may promote lipid sparing. Finally, embryos that have been in diapause for 10 days show a substantially different pattern of mRNA expression compared with either pre-diapause or embryos not destined for diapause, with the majority of mRNAs examined being downregulated. These transcript levels in later diapause suggest that a number of upregulated genes in pre-diapause are transiently expressed and are less essential as diapause progresses.

Cloning and expression of the gene encoding the diapause hormone and pheromone biosynthesis activating neuropeptide of the beet armyworm,Spodoptera exigua

Diapause hormone (DH) and pheromone biosynthesis activating neuropeptide (PBAN), two important insect neuropeptides, regulate insect development and sex pheromone biosynthesis, respectively. DH-like immunoreactivity has been detected in the suboesophageal ganglion (SG) of pharate adult of Spodoptera exigua (Spe) by using an antiserum against Helicoverpa armigera DH. A full-length of Spe-DH-PBAN cDNA was obtained based on reverse transcription-PCR and rapid amplification of cDNA ends strategies. The open reading frame of this cDNA encodes a 197-amino acid precursor protein that contains DH, PBAN, and three other SG neuropeptides, all of which share a conservative C-terminal pentapeptide motif FXPR/KL (X = G, T or S). Northern blot analysis demonstrates the presence of an 800 bp transcript in the SG. The Spe-DH-PBAN mRNA is detectable at high levels at larval and adult stages, suggesting that Spe-DH-PBAN gene might be correlated with larval development and sex pheromone biosynthesis in moths.

Identification and characterization of a POU transcription factor in the cotton bollworm, Helicoverpa armigera

Background

The POU family genes containing the POU domain are common in vertebrates and invertebrates and play critical roles in cell-type-specific gene expression and cell fate determination.

Results

Har-POU, a new member of the POU gene family, was cloned from the suboesophageal ganglion of Helicoverpa armigera (Har), and its potential functions in the development of the central nervous system (CNS) were analyzed. Southern blot analysis suggests that a single copy of this gene is present in the H. armigera haploid genome. Har-POU mRNA is distributed widely in various tissues and expressed highly in the CNS, salivary gland, and trachea. In vitro-translated Har-POU specifically bound canonical octamer motifs on the promoter of diapause hormone and pheromone biosynthesis activating neuropeptide (DH-PBAN) gene in H. armigera. Expression of the Har-POU gene is markedly higher in the CNS of nondiapause-destined pupae than in diapause-destined pupae. Expression of the Har-POU gene in diapausing pupae was upregulated quickly by injection of ecdysone.

Conclusion

Har-POU may respond to ecdysone and bind to the promoter of DH-PBAN gene to regulate pupal development in H. armigera.

The Pitx homeobox gene in Bombyx mori: Regulation of DH-PBAN neuropeptide hormone gene expression

The diapause hormone-pheromone biosynthesis activating neuropeptide gene, DH-PBAN, is expressed exclusively in seven pairs of DH-PBAN-producing neurosecretory cells (DHPCs) on the terminally differentiated processes of the subesophageal ganglion (SG). To help reveal the regulatory mechanisms of cell-specific DH-PBAN expression, we identified a cis-regulatory element that regulates expression in DHPCs using the recombinant AcNPV-mediated gene transfer system and a gel-mobility shift assay. Bombyx mori Pitx (BmPitx), a bicoid-like homeobox transcription factor, binds this element and activates DH-PBAN expression. The BmPitx was expressed in various tissues, including DHPCs in the SG. Suppression of DH-PBAN expression by silencing of the BmPitx successfully induced non-diapaused eggs from a diapause egg producer. To the best of our knowledge, this report is the first to identify a neuropeptide-encoding gene as a target of the Pitx transcriptional regulator in invertebrates. Thus, it is tempting to speculate that functional conservation of Pitx family members on neuropeptide gene expression occurs through a "combinational code mechanism" in both vertebrate and invertebrate in neuroendocrine systems.

Protein–DNA interactions in the promoter region of the gene encoding diapause hormone and pheromone biosynthesis activating neuropeptide of the cotton bollworm, Helicoverpa armigera

Diapause hormone (DH) and pheromone biosynthesis activating neuropeptide (PBAN) are two crucial neuropeptides which regulate insect development and sex pheromone biosynthesis respectively. These peptides are encoded by a single gene, termed DH-PBAN gene. In this study, we characterized the promoter of the DH-PBAN gene in Helicoverpa armigera (Har). Transient transfection assays using a series of stepwise deletion fragments linked to the luciferase reporter gene indicate that the promoter contains multiple regulator domains that can activate and repress reporter gene expression. The fragment spanning -467 to -371 bp of the DH-PBAN promoter is an activator domain of transcription, whereas the region from -965 to -534 bp represses the promoter activity in the insect cell line BmN. Electrophoretic mobility shift assays demonstrate that at least two nuclear protein factors from the nuclear protein extracts of H. armigera suboesophageal ganglion, Har-DHMBP-1 and-2 (DH-modulator-binding protein) can specifically bind to the activating region. Furthermore, we characterized in detail that the nuclear protein factor Har-DHMBP-3 can specifically bind to a classical E-box, CAGCTG localized at positions -360 to -355 bp, a potential site for interaction with basic helix-loop-helix transcription factors. Mutation of this E-box results in a significant reduction of the promoter activity, suggesting it can modulate the previously identified activator domain. Taken together, multipartite cis-elements and transcription factors in the DH-PBAN promoter are involved in regulation of the gene expression.

Tick pheromones and their use in tick control

Tick pheromones that regulate assembly, attraction/aggregation/attachment, and mating behavior have been described. Most of the compounds regulating these behaviors are purines, substituted phenols, or cholesteryl esters. Other pheromonal compounds include organic acids, hematin, or ecdysteroids. Novel devices have been developed that combine the specific compounds comprising these pheromones with an acaricide. When applied to tick-infested vegetation or directly to the body surfaces of livestock or companion animals, these devices are effective for tick control. This review summarizes the current state of knowledge of tick pheromones. In addition, this review also presents examples illustrating how devices using tick pheromones can offer effective alternatives to conventional methods for achieving tick control.

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.

Myocyte enhancer factor 2 (MEF2) is a key modulator of the expression of the prothoracicotropic hormone gene in the silkworm, Bombyx mori

Prothoracicotropic hormone (PTTH) plays a central role in controlling molting, metamorphosis, and diapause termination in insects by stimulating the prothoracic glands to synthesize and release the molting hormone, ecdysone. Using Autographa californica nucleopolyhedrovirus (AcNPV)-mediated transient gene transfer into the central nervous sytem (CNS) of the silkworm, Bombyx mori, we identified two cis-regulatory elements that participate in the decision and the enhancement of PTTH gene expression in PTTH-producing neurosecretory cells (PTPCs). The cis-element mediating the enhancement of PTTH gene expression binds the transcription factor Bombyx myocyte enhancer factor 2 (BmMEF2). The BmMEF2 gene was expressed in various tissues including the CNS. In brain, the BmMEF2 gene was expressed at elevated levels in two types of lateral neurosecretory cells, namely PTPCs and corazonin-like immunoreactive lateral neurosecretory cells. Overexpression of BmMEF2 cDNA caused an increase in the transcription of PTTH. Therefore, BmMEF2 appears to be particularly important in the brain where it is responsible for the differentiation of lateral neurosecretory cells, including the enhancement of PTTH gene expression. This is the first report to identify a target gene of MEF2 in the invertebrate nervous system.

The analysis of differentially expressed novel transcripts in diapausing and diapause-activated eggs of Bombyx mori

As an initial step to define the molecular mechanism of initiation and termination of diapause during the embryogenesis of silkworms, Bombyx mori, mRNA transcripts from maintained and activated diapause eggs were compared with differential expression using cDNA array. Twenty-four individual cDNA transcripts were expressed differentially in a total of 1,468 different cDNAs. Among those clones, mRNA transcript from cytochrome oxidase subunit I (COI), which was detected to be 2-kb transcripts, gradually increased in diapause-activated eggs during early embryogenesis. Further analysis revealed that mRNA transcripts from silkworm COI were highly expressed in testis, fat body, and midgut during the larval stage. These results may indicate that the expression of silkworm COI mRNA is regulated developmentally as well as tissue-specifically.

Structural characterization and transcriptional regulation of the gene encoding diapause hormone and pheromone biosynthesis activating neuropeptide in the cotton bollworm, Helicoverpa armigera

We have cloned the gene encoding the diapause hormone and the pheromone biosynthesis activating neuropeptide in Helicoverpa armigera (Har-DH-PBAN). The Har-DH-PBAN gene contains six exons and five introns that fall in the same positions as in the Bombyx mori DH-PBAN gene (Bom-DH-PBAN). The transcription initiation site lays 29 bp upstream of the translation initiation site. Southern blot analysis suggests that a single copy of this gene is present per haploid genome. A structural comparison of DH-PBAN promoters between H. armigera and B. mori show similarities in the TATA box and in a potential binding site for a POU family transcription factor, POU-M2. However, testing of these DNA regions for factor binding in vitro and transcription assays in cell culture highlight significant differences in their regulation particularly in reference to the POU-M2 sites. Our results uncover common and different regulatory mechanisms at work in the control of DH-PBAN gene expression in H. armigera and B. mori.

Developmental expression of FXPRLamide neuropeptides in peptidergic neurosecretory cells of diapause- and nondiapause-destined individuals of the cotton bollworm, Helicoverpa armigera

The diapause hormone (DH)-pheromone biosynthesis activating neuropeptide (PBAN) gene encodes five neuropeptides, DH, PBAN, alpha-SGNP, beta-SGNP, and gamma-SGNP (subesophageal ganglion neuropeptide). All share the C-terminal pentapeptide FXPRLamide sequence and are produced in the subesophageal ganglion (SG). Expression of the DH-PBAN gene in the central nervous system of embryonic, larval, pupal, and adult Helicoverpa armigera (Har) was studied using in situ hybridization, whole-mount immunocytochemistry, and competitive ELISA. Both Har-DH-PBAN mRNA and protein are localized in the mandibular, maxillary, and labial cell clusters of the SG and a pair of ventral midline neurons of each thoracic ganglion. The FXPRLamide titers in hemolymph are significantly higher in diapause-destined larvae during the fifth and sixth instar than in similar nondiapause-destined individuals. In contrast, the FXPRLamide titers in diapause-destined pupae are significantly lower than in nondiapause-destined pupae. The results from immunocytochemistry and in situ hybridization are consistent with changes of FXPRLamide titers as measured by ELISA. These data suggest that the expression of DH-PBAN might be correlated with diapause induction at the larval stage of diapause-destined individuals and continuous development at pupal stage of nondiapause-destined individuals. Thus, the DH-PBAN gene may play an important regulatory role in aspects of insect development besides diapause termination and pheromone biosynthesis. The transport pathways of FXPRLamide neuropeptides suggest that humoral route is involved in their regulation of development.

Establishment of a Sandwich ELISA System to Detect Diapause Hormone, and Developmental Profile of Hormone Levels in Egg and Subesophageal Ganglion of the Silkworm, Bombyx mori

In the silkworm Bombyx mori, diapause hormone (DH) is produced in the female subesophageal ganglion (SG) and induces embryonic diapause by targeting developing ovaries. DH is processed from a precursor protein consisting of DH, pheromone biosynthesis activating neuropeptide (PBAN) and three other neuropeptides (SGNPs). Because these five neuropeptides share a common sequence, FXPRLamide, at the C-terminus, a direct and specific assay for DH itself is required in order to understand the profile of concentration changes. In this study, we produced a mouse monoclonal antibody (anti-DH[N] mAb) against the N-terminal region of DH and developed a sandwich enzyme-linked immunosorbent assay using the anti-DH[N] mAb and a rabbit polyclonal antibody against the C-terminus of DH. This procedure enabled us to specifically quantify the DH molecule at femtomolar levels (equivalent to 1/10 of SG). We then plotted DH levels in eggs and SGs during embryonic and post-embryonic development. DH was present in late-stage embryos that had been destined for the production of both diapause and nondiapause eggs. DH levels in SG gradually increased in both types during larval development and peaked at the early pupal stage. At the middle pupal stage, DH levels in SG and SG-brain complex decreased markedly in the diapause-egg producing type, thus indicating active release of DH into the hemolymph. From 5th instar larva to adult, no sexual differences in DH levels were observed in SGs or SG-brain complexes from diapause and nondiapause egg-producing types.

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.

Molecular cloning, developmental expression, and tissue distribution of the gene encoding DH, PBAN and other FXPRL neuropeptides in Samia cynthia ricini

We obtained a full-length cDNA encoding diapause hormone (DH) and pheromone biosynthesis activating neuropeptide (PBAN) in Samia cynthia ricini based on both reverse transciptase-PCR (RT-PCR) and rapid amplification of cDNA ends (RACE) strategies. The open reading frame (ORF) of this cDNA encodes a 198-amino acid precursor protein that contains a 33-aa PBAN, a 24-aa DH-like peptide, and three other neuropeptides, all of which share a common C-terminal pentapeptide motif FXPR/KL (X = G, T, S). Samia DH-like and PBAN show high homology to their counterpart in other Lepidoptera. Northern blots demonstrate the presence of a 0.8-kb transcript in the suboesophageal ganglion (SG). The DH-PBAN mRNA was detectable at much lower levels in other neural tissues, such as brain and thoracic ganglia (TG), but not in non-neural tissue, such as the midgut, silk gland, fat body or epidermis. The DH-PBAN mRNA content in the SG was measured using the combined method of quantitative RT-PCR and Southern blotting and was shown to vary with developmental stage. Using an antiserum against Helicoverpa armigera PBAN, PBAN-like immunoreactivity was detected in the SG, TG and terminal abdomen ganglion of S. cynthia ricini by whole-mount immunocytochemistry. The changes of PBAN-like immunoreactivity in the hemolymph are consistent with PBAN transcripts in the SG during pupal development. PBAN increases quickly at adult eclosion, an observation that is consistent with PBAN's key role in pheromone biosynthesis, and synthetic PBAN or brain-SG extracts successfully stimulates pheromone biosynthesis in decapitated moths.

Identification of a POU factor involved in regulating the neuron-specific expression of the gene encoding diapause hormone and pheromone biosynthesis-activating neuropeptide in Bombyx mori

Diapause hormone (DH) and PBAN (pheromone biosynthesis-activating neuropeptide) are two important insect neuropeptides regulating development and reproduction respectively. In the present study, we report two Bombyx mori transcription factors interacting specifically with the promoter of Bom-DH-PBAN (where Bom-DH stands for B. mori DH); we named them DHMBP-1 and -2 (DH-modulator-binding proteins 1 and 2). The developmental changes of DHMBP-1/-2 are closely correlated with that of Bom-DH-PBAN mRNA throughout the pupal stage. Competition assays indicate that DHMBP-1 from Chinese B. mori possesses binding characteristics similar to those of the POU-M1 protein from Japanese B. mori. POU-M1 cDNAs were cloned from various tissues of Chinese B. mori and were found to be distinct from the previously published POU-M1 in amino acid residues 108-136 because of insertion mutations. Owing to this difference in amino acid residues, we named this cDNA POU-M2. Even though POU-M2 differs from POU-M1 at the N-terminal, the POU domain and the binding properties of both POU-M1 and -M2 are the same. Functional analysis showed that overexpression of POU-M2 in the Bombyx cell line BmN activated the promoter of Bom-DH-PBAN, but failed to activate a promoter in which the POU-binding element was mutated. The transcriptional activity of POU-M2 is probably regulated by other factors binding to the upstream of the promoter sequence. We show that the POU-M2-binding site was able to activate the transcription of a heterologous promoter of the gene encoding B. mori larval serum protein. POU-M1 was found to exhibit the same transcriptional activities as POU-M2. Taken together, these results demonstrate that POU-M2 plays an important role in the transcriptional regulation of the Bom-DH-PBAN gene.

The diapause hormone-pheromone biosynthesis activating neuropeptide gene of Helicoverpa armigera encodes multiple peptides that break, rather than induce, diapause

FXPRLamide peptides encoded by the DH-PBAN (diapause hormone-pheromone biosynthesis activating neuropeptide) gene induce embryonic diapause in Bombyx mori, but terminate pupal diapause in Helicoverpa armigera (Har). Here, we explore the mechanisms of terminating pupal diapause by the FXPRLamide peptides. Using quantitative RT-PCR, we observed that expression of Har-DH-PBAN mRNA in the SG of nondiapause-type pupae was significantly higher than in diapause-type pupae. Immunocytochemical results indicated that the level of FXPRLamide peptides and axonal release are related to the diapause decision. Ecdysteroidogenesis in prothoracic glands (PGs) was stimulated by synthetic Har-DH in vivo and in vitro, and labeled Har-DH bound to the membrane of the PG, thus suggesting that DH breaks diapause by activating the PG to synthesize ecdysone. Furthermore, the response of DH in terminating diapause was temperature dependent. Decerebration experiments showed that the brain can control pupal development through the regulation of DH, and DH can terminate diapause and promote development without the brain. This result suggests a possible mechanism of response for the signals of DH and other FXPRLamide peptides in H. armigera.

Functional analysis of the SGNP I in the pupal diapause of the oriental tobacco budworm, Helicoverpa assulta (Lepidoptera: Noctuidae)

Helicoverpa assulta suboesophageal ganglion neuropeptide I (Has-SGNP I) is a 24-amino acids peptide amide, which shows 62.5% similarity with the diapause hormone of Bombyx mori (Bom-DH). It has been demonstrated that embryonic diapause is induced by DH in B. mori. Injection of synthetic amidated Has-SGNP I terminated pupal diapause in a dose-dependent manner. Therefore, Has-SGNP I might be referred to a "diapause termination hormone" in H. assulta (Has-DTH). The maximal dose of Has-DTH for diapause termination was 1.0 microg and the half-maximal dose 0.4 microg. The time required for diapause termination of Has-DTH was 2-3 days longer than that of 20-hydroxyecdysone. During the pupal stage, DTH mRNA content in the SGs of nondiapausing pupae was always higher than in diapausing pupae using the combined method of quantitative RT-PCR and Southern blot. DTH gene also expressed at a low level while diapausing pupae were chilled at 4 degrees C, but increased rapidly and largely after being transferred to 25 degrees C. Using a competitive ELISA, Has-DTH-like immunoreactivity in the haemolymph showed the same pattern as that of Has-DTH gene expression. Those results indicated that Has-DTH gene expression was related to diapause development and could be activated by low temperature. Has-DTH might be useful to elucidate the mechanism of diapause termination in pupal diapause species.

Cloning and expression of the cDNA encoding the FXPRL family of peptides and a functional analysis of their effect on breaking pupal diapause in Helicoverpa armigera

Diapause hormone (DH) and pheromone biosynthesis activating neuropeptide (PBAN) are encoded by a single mRNA in the suboesophegeal ganglion (SG) and are responsible for induction of embryonic diapause in Bombyx mori and sex pheromone biosynthesis in lepidopteran insects. PBAN cDNA analyses revealed that the DH-like peptide is present in several species that have a pupal diapause. However, the function of the DH-like peptide remains unknown. In the present study, we cloned the cDNA encoding DH-PBAN in Helicoverpa armigera utilizing the rapid amplification of the cDNA ends method. The nucleotide se quence analysis revealed that the longest open reading frame of this cDNA encodes a 194-amino acid precursor protein that con tains a 33-aa PBAN, a 24-aa DH-like peptide, and three other neuropeptides, all of which have a common C-terminal pentapeptide motif FXPR/KL ( X=G, T, S). A homology search showed that H. armigera DH-like and PBAN are highly homologous to those from other insects. Northern blot analysis demonstrated a single message RNA corresponding to the size of Har-DH-PBAN cDNA from pupal SG with significantly higher expression in the SG of nondiapause pupae than diapausing pupae. Western blot analysis showed DH-like peptide expression from SG of both males and females. When DH-like peptide was injected into nondiapause larvae and pupae, it did not induce diapause, but rather efficiently broke pupal diapause in H. armigera. The ED(50) of DH to terminate pupal diapause is 20 pmol/pupae. The other four FXPRLamide neuropeptides from the DH-PBAN polyprotein precursor have cross activity for diapause termination. These observations therefore suggest a potential role for these FXPRL family peptides in promoting continuous development in several noctuid species. The high expression of this gene in pharate adults and adults indicates that the FXPRL family peptides may have multiple physiological functions.

Molecular characterization of prothoracicotropic hormone and diapause hormone in Heliothis virescens during diapause, and a new role for diapause hormone

cDNAs encoding prothoracicotropic hormone (PTTH) and diapause hormone (DH) were isolated from the tobacco budworm, Heliothis virescens (Hvi). Hvi-PTTH cDNA reveals key structural features known from other PTTHs, yet there is a > 30% amino acid difference between the PTTH sequences found in this noctuid when compared with the PTTHs known from Bombycoidea. Hvi-DH-PBAN cDNA encodes a precursor protein including a DH-like peptide, pheromone biosynthesis-activating neuropeptide (PBAN) and three additional neuropeptides with an FXPRL sequence at the C terminus. PTTH and DH-PBAN transcripts are most highly expressed in the brain and subesophageal ganglion (SG), respectively. Expression of both the PTTH and the DH-PBAN transcripts is high in larvae and remains high in nondiapausing pupae, but in larvae programmed for pupal diapause, expression declines sharply at the onset of larval wandering behaviour and remains low during pupal diapause. This pattern implies that both of these genes are shut down during diapause. These results are not consistent with a role for DH in promoting the entry into diapause as noted in Bombyx mori. Instead, the higher expression of DH in nondiapausing pupae suggests a possible role for DH in promoting continuous development. The injection of DH into diapausing pupae did indeed successfully terminate diapause, thus suggesting a possible new role for this neuropeptide.

Neuropeptides in the nervous system of Drosophila and other insects: multiple roles as neuromodulators and neurohormones

Neuropeptides in insects act as neuromodulators in the central and peripheral nervous system and as regulatory hormones released into the circulation. The functional roles of insect neuropeptides encompass regulation of homeostasis, organization of behaviors, initiation and coordination of developmental processes and modulation of neuronal and muscular activity. With the completion of the sequencing of the Drosophila genome we have obtained a fairly good estimate of the total number of genes encoding neuropeptide precursors and thus the total number of neuropeptides in an insect. At present there are 23 identified genes that encode predicted neuropeptides and an additional seven encoding insulin-like peptides in Drosophila. Since the number of G-protein-coupled neuropeptide receptors in Drosophila is estimated to be around 40, the total number of neuropeptide genes in this insect will probably not exceed three dozen. The neuropeptides can be grouped into families, and it is suggested here that related peptides encoded on a Drosophila gene constitute a family and that peptides from related genes (orthologs) in other species belong to the same family. Some peptides are encoded as multiple related isoforms on a precursor and it is possible that many of these isoforms are functionally redundant. The distribution and possible functions of members of the 23 neuropeptide families and the insulin-like peptides are discussed. It is clear that each of the distinct neuropeptides are present in specific small sets of neurons and/or neurosecretory cells and in some cases in cells of the intestine or certain peripheral sites. The distribution patterns vary extensively between types of neuropeptides. Another feature emerging for many insect neuropeptides is that they appear to be multifunctional. One and the same peptide may act both in the CNS and as a circulating hormone and play different functional roles at different central and peripheral targets. A neuropeptide can, for instance, act as a coreleased signal that modulates the action of a classical transmitter and the peptide action depends on the cotransmitter and the specific circuit where it is released. Some peptides, however, may work as molecular switches and trigger specific global responses at a given time. Drosophila, in spite of its small size, is now emerging as a very favorable organism for the studies of neuropeptide function due to the arsenal of molecular genetics methods available.

Two nitridergic peptides are encoded by the gene capability in Drosophila melanogaster

A Drosophila gene (capability, capa) at 99D on chromosome 3R potentially encodes three neuropeptides: GANMGLYAFPRV-amide (capa-1), ASGLVAFPRV-amide (capa-2), and TGPSASSGLWGPRL-amide (capa-3). Capa-1 and capa-2 are related to the lepidopteran hormone cardioacceleratory peptide 2b, while capa-3 is a novel member of the pheromone biosynthesis-activating neuropeptide/diapause hormone/pyrokinin family. By immunocytochemistry, we identified four pairs of neuroendocrine cells likely to release the capa peptides into the hemolymph: one pair in the subesophageal ganglion and the other three in the abdominal neuromeres. In the Malpighian (renal) tubule, capa-1 and capa-2 increase fluid secretion rates, stimulate nitric oxide production, and elevate intracellular Ca(2+) and cGMP in principal cells. Capa-stimulated fluid secretion, but not intracellular Ca(2+) concentration rise, is inhibited by the guanylate cyclase inhibitor methylene blue. The actions of capa-1 and capa-2 are not synergistic, implying that both act on the same pathways in tubules. The capa gene is thus the first to be shown to encode neuropeptides that act on renal fluid production through nitric oxide.

IDENTIFICATION, SEQUENCE AND EXPRESSION OF A CRUSTACEAN CARDIOACTIVE PEPTIDE (CCAP) GENE IN THE MOTHMANDUCA SEXTA

The crustacean cardioactive peptide (CCAP) gene was isolated from the tobacco hawkmoth Manduca sexta. The gene has an open reading frame of 125 amino acid residues containing a single, complete copy of CCAP. Analysis of the gene structure revealed three introns interrupting the coding region. A comparison of the M. sexta CCAP gene with the Drosophila melanogaster genome database reveals significant similarities in sequence and gene structure.

The spatial and temporal expression patterns of the CCAP gene in the M. sexta central nervous system were determined in all major post-embryonic stages using in situ hybridization techniques. The CCAP gene is expressed in a total of 116 neurons in the post-embryonic M. sextacentral nervous system. Nine pairs of cells are observed in the brain, 4.5 pairs in the subesophageal ganglion, three pairs in each thoracic ganglion(T1-T3), three pairs in the first abdominal ganglion (A1), five pairs each in the second to sixth abdominal ganglia (A2-A6) and 7.5 pairs in the terminal ganglion. The CCAP gene is expressed in every ganglion in each post-embryonic stage, except in the thoracic ganglia of first- and second-instar larvae. The number of cells expressing the CCAP gene varies during post-embryonic life,starting at 52 cells in the first instar and reaching a maximum of 116 shortly after pupation. One set of thoracic neurons expressing CCAP mRNA shows unusual variability in expression levels immediately prior to larval ecdysis. Using previously published CCAP immunocytochemical data, it was determined that 91 of 95 CCAP-immunopositive neurons in the M. sexta central nervous system also express the M. sexta CCAP gene, indicating that there is likely to be only a single CCAP gene in M. sexta.

Neuropeptides and neuropeptide receptors in the Drosophila melanogaster genome

Recent genetic analyses in worms, flies, and mammals illustrate the importance of bioactive peptides in controlling numerous complex behaviors, such as feeding and circadian locomotion. To pursue a comprehensive genetic analysis of bioactive peptide signaling, we have scanned the recently completed Drosophila genome sequence for G protein-coupled receptors sensitive to bioactive peptides (peptide GPCRs). Here we describe 44 genes that represent the vast majority, and perhaps all, of the peptide GPCRs encoded in the fly genome. We also scanned for genes encoding potential ligands and describe 22 bioactive peptide precursors. At least 32 Drosophila peptide receptors appear to have evolved from common ancestors of 15 monophyletic vertebrate GPCR subgroups (e.g., the ancestral gastrin/cholecystokinin receptor). Six pairs of receptors are paralogs, representing recent gene duplications. Together, these findings shed light on the evolutionary history of peptide GPCRs, and they provide a template for physiological and genetic analyses of peptide signaling in Drosophila.

Structure of the VAP-peptide (BmACP-6.7) gene in the silkworm, Bombyx mori and a possible regulation of its expression by BmFTZ-F1

The VAP-peptide (BmACP-6.7) is a hydrophobic peptide localized in adult cuticle of the silkworm, Bombyx mori. We isolated and characterized the VAP-peptide gene as a useful marker gene to analyze molecular mechanisms of terminal differentiation processes in the adult. The gene is composed of two exons interrupted by one intron. The 5' upstream promoter region is shown to bear a nucleotide sequence similar to the cis-element that is recognized and bound by the Bombyx mori FTZ-F1 protein (BmFTZ-F1). Expression of the BmFTZ-F1 gene preceded expression of the VAP-peptide gene and injection of 20-hydroxyecdysone suppressed the expression of both genes. An in vitro binding assay indicated direct interaction of BmFTZ-F1 with the VAP-peptide gene promoter sequence. Therefore, BmFTZ-F1 is proposed to be a possible factor regulating the stage-specific expression of the VAP-peptide gene towards adult life.

Genetic mapping of RAPD markers linked to the densonucleosis refractoriness gene, nsd-1, in the silkworm, Bombyx mori

In the silkworm, Bombyx mori, nonsusceptibility to B. mori densonucleosis virus type-1 (BmDNV-1) is controlled by a recessive gene, nsd-1 (nonsusceptibility to DNV-1), located on the twenty-first chromosome. We investigated genetic linkage between five random amplified polymorphic DNA (RAPD) markers and the +nsd-1 gene. Initially, we constructed the CSD-1 strain (nsd-1/+) which is congenic to strain C137 (nsd-1/nsd-1) for the twenty-first chromosome, starting with a female of C137 and a male of strain J137 (+nsd-1/+nsd-1). For the crossing over experiment, a female of C137 was crossed with a male (nsd-1/+) of CSD-1. Segregation analysis showed that the most closely linked RAPD marker mapped 3.0 cM distant from +nsd-1. A more specific marker for +nsd-1 was made by converting this RAPD band into a sequence characterized amplified region (SCAR) using a series of newly designed primer pairs based on its DNA sequence.