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

Photoperiodism of Diapause Induction in the Silkworm, Bombyx mori

The silkworm Bombyx mori exhibits a photoperiodic response (PR) for embryonic diapause induction. This article provides a comprehensive review of literature on the silkworm PR, starting from early works on population to recent studies uncovering the molecular mechanism. Makita Kogure (1933) conducted extensive research on the PR, presenting a pioneering paper on insect photoperiodism. In the 1970s and 80s, artificial diets were developed, and the influence of nutrition on PR was well documented. The photoperiodic photoreceptor has been investigated from organ to molecular level in the silkworm. Culture experiments demonstrated that the photoperiodic induction can be programmed in an isolated brain (Br)-subesophageal ganglion (SG) complex with corpora cardiaca (CC)-corpora allata (CA). The requirement of dietary vitamin A for PR suggests the involvement of opsin pigment in the photoperiodic reception, and a cDNA encoding an opsin (Boceropsin) was cloned from the brain. The effector system concerning the production and secretion of diapause hormone (DH) has also been extensively investigated in the silkworm. DH is produced in a pair of posterior cells of SG, transported to CC by nervi corporis cardiaci, and ultimately released into the hemolymph. Possible involvement of GABAergic and corazonin (Crz) signal pathways was suggested in the control of DH secretion. Knockout (KO) experiments of GABA transporter (GAT) and circadian clock genes demonstrated that GAT plays a crucial role in PR through circadian control. A model outlining the PR mechanism, from maternal photoperiodic light reception to DH secretion, has been proposed.

RNA N6-methyladenosine of DHAPAT and PAP involves in regulation of diapause of Bombyx mori via the lipid metabolism pathway

Environment-induced epigenetics are involved in diapause regulation, but the molecular mechanism that epigenetically couples nutrient metabolism to diapause regulation remains unclear. In this study, we paid special attention to the significant differences in the level of N6-adenosine methylation (m6A) of dihydroxyacetone phosphate acyltransferase (DHAPAT) and phosphatidate phosphatase (PAP) genes in the lipid metabolism pathway of the bivoltine silkworm (Bombyx mori) strain Qiufeng developed from eggs incubated at a normal temperature (QFHT, diapause egg producer) compared to those from eggs incubated at a low temperature (QFLT, non-diapause egg producer). We knocked down DHAPAT in the pupal stage of the QFLT group, resulting in the non-diapause destined eggs becoming diapausing eggs. In the PAP knockdown group, the colour of the non-diapause destined eggs changed from light yellow to pink 3 days after oviposition, but they hatched as normal. Moreover, we validated that YTHDF3 binds to m6A-modified DHAPAT and PAP mRNAs to promote their stability and translation. These results suggest that RNA m6A methylation participates in the diapause regulation of silkworm by changing the expression levels of DHAPAT and PAP and reveal that m6A epigenetic modification can be combined with a lipid metabolism signal pathway to participate in the regulation of insect diapause traits, which provides a clearer image for exploring the physiological basis of insect diapause.

m6A-dependent mevalonate kinase in juvenile hormone synthesis pathway regulates the diapause process of bivoltine silkworm (Bombyx mori)

BACKGROUND

Research has shown that epigenetic modification are involved the regulation of diapause in bivoltine silkworms (Bombyx mori), but it remains unclear how epigenetic modification in response to environmental signals precisely to regulate the diapause processing of bivoltine B. mori.

METHODS AND RESULTS

In this study, the diapause terminated eggs of bivoltine B. mori, Qiufeng (QF) were divided into two groups: a QFHT group incubated at 25 °C with a natural day/night cycle to produce diapause eggs, and a QFLT group incubated at 16.5 °C in darkness to produce non-diapause eggs. On the 3rd day of the pupal stage, the total RNAs of the eggs were extracted and their N6-adenosine methylation (m⁶A) abundances were analyzed to explore the effects of m⁶A methylation on diapause in the silkworm. The results showed that 1984 m⁶A peaks are shared, 1563 in QFLT and 659 in QFHT. The m⁶A methylation level of the QFLT group was higher than that of the QFHT one in various signaling pathways. The m⁶A methylation rate of mevalonate kinase (MK) in the insect hormone synthesis pathway was significantly different between the two groups. The knockdown of MK by RNA interference in the pupae of QFLT resulted in females laying diapause eggs rather than non-diapause eggs after mating.

CONCLUSIONS

m⁶A methylation involves in the diapause regulation of bivoltine B. mori by changing the expression levels of MK. This result provides a clearer image of the environmental signals on the regulation of diapause in bivoltine silkworms.

Circadian Clock Gene Period Contributes to Diapause via GABAeric-Diapause Hormone Pathway in Bombyx mori

Diapause is a developmental transition in insects based on seasonal adaptation to adversity; it is regulated by a circadian clock system and the endocrine system. However, the molecular node and its mechanism underlying the effects of these systems are still unclear. Here, a mutant of Bombyx mori with the circadian clock gene Period (Per) knocked out was constructed, which dramatically changed the classic diapause-destined pathway. Per-knockout silkworms powerfully attenuated, but could not completely block, the predetermined effects of temperature and photoperiod on diapause determination, and this effect depended on the diapause hormone (DH) pathway. The impaired transcription-translation feedback loop of the circadian clock system lacking the Per gene caused direct up-regulation of the expression of GRD, a receptor of γ-aminobutyric acid (GABA), by changing expression level of Cycle. The synthesis of GABA in the tissue complex of brain-suboesophageal ganglion then increased and restricted the decomposition, which continuously promoted the GABAergic signal to play a role, and finally inhibiting (delaying) the release of DH to the hemolymph, and reducing the diapause-inducing effect of DH. The results provided an example to explain the regulatory mechanism of the circadian clock on endocrine hormones in the silkworm.

Maternal GABAergic and GnRH/corazonin pathway modulates egg diapause phenotype of the silkworm Bombyx mori

Diapause represents a major developmental switch in insects and is a seasonal adaptation that evolved as a specific subtype of dormancy in most insect species to ensure survival under unfavorable environmental conditions and synchronize populations. However, the hierarchical relationship of the molecular mechanisms involved in the perception of environmental signals to integration in morphological, physiological, behavioral, and reproductive responses remains unclear. In the bivoltine strain of the silkworm Bombyx mori, embryonic diapause is induced transgenerationally as a maternal effect. Progeny diapause is determined by the environmental temperature during embryonic development of the mother. Here, we show that the hierarchical pathway consists of a γ-aminobutyric acid (GABA)ergic and corazonin signaling system modulating progeny diapause induction via diapause hormone release, which may be finely tuned by the temperature-dependent expression of plasma membrane GABA transporter. Furthermore, this signaling pathway possesses similar features to the gonadotropin-releasing hormone (GnRH) signaling system for seasonal reproductive plasticity in vertebrates.

Agonist-mediated activation of Bombyx mori diapause hormone receptor signals to extracellular signal-regulated kinases 1 and 2 through Gq-PLC-PKC-dependent cascade

Diapause is a developmental strategy adopted by insects to survive in challenging environments such as the low temperatures of a winter. This unique process is regulated by diapause hormone (DH), which is a neuropeptide hormone that induces egg diapause in Bombyx mori and is involved in terminating pupal diapause in heliothis moths. An G protein-coupled receptor from the silkworm, B. mori, has been identified as a specific cell surface receptor for DH. However, the detailed information on the DH-DHR system and its mechanism(s) involved in the induction of embryonic diapause remains unknown. Here, we combined functional assays with various specific inhibitors to elucidate the DHR-mediated signaling pathways. Upon activation by DH, B. mori DHR is coupled to the Gq protein, leading to a significant increase of intracellular Ca(2+) and cAMP response element-driven luciferase activity in an UBO-QIC, a specific Gq inhibitor, sensitive manner. B. mori DHR elicited ERK1/2 phosphorylation in a dose- and time-dependent manner in response to DH. This effect was almost completely inhibited by co-incubation with UBO-QIC and was also significantly suppressed by PLC inhibitor U73122, PKC inhibitors Gö6983 and the Ca(2+) chelator EGTA. Moreover, DHR-induced activation of ERK1/2 was significantly attenuated by treatment with the Gβγ specific inhibitors gallein and M119K and the PI3K specific inhibitor Wortmannin, but not by the Src specific inhibitor PP2. Our data also demonstrates that the EGFR-transactivation pathway is not involved in the DHR-mediated ERK1/2 phosphorylation. Future efforts are needed to clarify the role of the ERK1/2 signaling pathway in the DH-mediated induction of B. mori embryonic diapause.

Disruption of diapause induction by TALEN-based gene mutagenesis in relation to a unique neuropeptide signaling pathway in Bombyx

The insect neuropeptide family FXPRLa, which carries the Phe-Xaa-Pro-Arg-Leu-NH2 sequence at the C-terminus, is involved in many physiological processes. Although ligand-receptor interactions in FXPRLa signaling have been examined using in vitro assays, the correlation between these interactions and in vivo physiological function is unclear. Diapause in the silkworm, Bombyx mori, is thought to be elicited by diapause hormone (DH, an FXPRLa) signaling, which consists of interactions between DH and DH receptor (DHR). Here, we performed transcription activator-like effector nuclease (TALEN)-based mutagenesis of the Bombyx DH-PBAN and DHR genes and isolated the null mutants of these genes in a bivoltine strain. All mutant silkworms were fully viable and showed no abnormalities in the developmental timing of ecdysis or metamorphosis. However, female adults oviposited non-diapause eggs despite diapause-inducing temperature and photoperiod conditions. Therefore, we conclude that DH signaling is essential for diapause induction and consists of highly sensitive and specific interactions between DH and DHR selected during ligand-receptor coevolution in Bombyx mori.

Embryonic thermosensitive TRPA1 determines transgenerational diapause phenotype of the silkworm, Bombyx mori

In the bivoltine strain of the silkworm, Bombyx mori, embryonic diapause is induced transgenerationally as a maternal effect. Progeny diapause is determined by the environmental temperature during embryonic development of the mother; however, its molecular mechanisms are largely unknown. Here, we show that the Bombyx TRPA1 ortholog (BmTrpA1) acts as a thermosensitive transient receptor potential (TRP) channel that is activated at temperatures above ∼ 21 °C and affects the induction of diapause in progeny. In addition, we show that embryonic RNAi of BmTrpA1 affects diapause hormone release during pupal-adult development. This study identifying a thermosensitive TRP channel that acts as a molecular switch for a relatively long-term predictive adaptive response by inducing an alternative phenotype to seasonal polyphenism is unique.

Changes in glutathione redox cycle during diapause determination and termination in the bivoltine silkworm, Bombyx mori

To explore whether glutathione regulates diapause determination and termination in the bivoltine silkworm Bombyx mori, we monitored the changes in glutathione redox cycle in the ovary of both diapause- and nondiapause-egg producers, as well as those in diapause eggs incubated at different temperatures. The activity of thioredoxin reductase (TrxR) was detected in ovaries but not in eggs, while neither ovaries nor eggs showed activity of glutathione peroxidase. A lower reduced glutathione/oxidized glutathione (GSH/GSSG) ratio was observed in the ovary of diapause-egg producers, due to weaker reduction of oxidized glutathione (GSSG) to the reduced glutathione (GSH) catalyzed by glutathione reductase (GR) and TrxR. This indicates an oxidative shift in the glutathione redox cycle during diapause determination. Compared with the 25°C-treated diapause eggs, the 5°C-treated diapause eggs showed lower GSH/GSSG ratio, a result of stronger oxidation of GSH catalyzed by thioredoxin peroxidase and weaker reduction of GSSG catalyzed by GR. Our study demonstrated the important regulatory role of glutathione in diapause determination and termination of the bivoltine silkworm.

Differential expression of the Bombyx mori diapause-termination timer gene Ea4 in diapause-inducing temperature and photoperiod

Diapause in Bombyx mori eggs is induced by temperature and photoperiod at the stage of embryonic development in the maternal generation. In those diapause eggs, Esterase-A4 is suggested to serve as a diapause-termination timer (TIME-EA4), because its ATPase activity shows an interval-timer elevation after acid treatment or chilling of eggs to break diapause. To clarify whether the timed ATPase activity of TIME-EA4 is related to its gene (Ea4) expression, we analyzed Ea4 mRNA of eggs in diapause-inducing environmental conditions. Reverse transcription PCR (RT-PCR) analysis showed that the level of Ea4 mRNA was lower in 15DD than in 25LL (P < 0.01) or in 20LD (P < 0.01) but did not oscillate when photoperiod and temperature periodically oscillated (P > 0.05). Furthermore, expressed sequence tag profile and gene microarray analysis demonstrated that Ea4 showed stage-specific and tissue-specific expression during postembryonic stages, high Ea4 mRNA in the spinning and eclosion stages, and in integument and head, but low in gonads of fifth-instar day-3 larvae. Then we analyzed the relationship between TIME-EA4 ATPase activities and Ea4 gene expression. The ATPase activities in diapause eggs laid by the resultant adults transiently elevated after treatments to break diapause, that is, at 1.5 h after common-acid treatment and day 13 after chilling at 5°C. However, these elevations of enzyme activities were not accompanied by any increases in Ea4 mRNA levels. In conclusion, the termination of the Bombyx embryonic diapause is related to TIME-EA4 but not to its gene expression.

Disappearance of chorion proteins from Bombyx mori eggs treated with HCl solution to prevent diapause

Bombyx mori eggs enter diapause immediately after completion of mesoderm segregation. HCl treatment of approximately 24-hour-old eggs (germband formation stage) is well known to be the most effective procedure to prevent entry into diapause, although the molecular mechanism remains unclear. In this study, we examined the protein composition of diapausing and nondiapausing eggs after various HCl treatments known to prevent or break diapause and found that proteins of approximately 11 and 8 kDa disappeared immediately after HCl treatment. Partial amino acid sequences of these proteins indicated that they were members of the chorion class A protein L12 family synthesized in follicle cells. Under the hypothesis that the chorion provides a barrier to oxygen, dechorionation of diapausing eggs induces resumption of embryonic development. Hence, to test this and other hypotheses about the function of these proteins, we used 20% SDS-PAGE with Coomassie Brilliant Blue staining to trace their disappearance from embryos and eggshells after treatment with HCl under different conditions and on polyvoltine, univoltine, and bivoltine silkworm races. Even when 10-day-old diapausing eggs were treated with HCl, which did not break diapause, the 11 and 8 kDa proteins disappeared. Our results suggest that disappearance of these proteins is not directly associated with preventing entry into or breaking a diapause state. Nevertheless, our results cannot completely rule out the possibility that the 11 and 8 kDa proteins function to block permeability of O(2) during the period when HCl treatment is physiologically effective to prevent diapause so that after the diapause system is established within the egg, even removing the 11 and 8 kDa proteins may not affect to prevent diapause. We also discuss the role of these proteins in choriogenesis.

Immunoreactive intensity of FXPRL amide neuropeptides in response to environmental conditions in the silkworm, Bombyx mori

In the silkworm Bombyx mori, the diapause hormone-pheromone biosynthesis activating neuropeptide gene, DH-PBAN, is a neuropeptide gene that encodes a polypeptide precursor consisting in five Phe-X-Pro-Arg-Leu-NH(2) (FXPRL) amide (FXPRLa) neuropeptides; DH (diapause hormone), PBAN (pheromone-biosynthesis-activating neuropeptide) and α-, β- and γ-SGNPs (subesophageal ganglion neuropeptides). These neuropeptides are synthesized in DH-PBAN-producing neurosecretory cells contained within three neuromeres, four mandibular cells, six maxillary cells, two labial cells (SLb) and four lateral cells of the subesophageal ganglion. DH is solely responsible, among the FXPRLa peptide family, for embryonic diapause. Functional differentiation has been previously suggested to occur at each neuromere, with the SLb cells releasing DH through brain innervation in order to induce embryonic diapause. We have investigated the immunoreactive intensity of DH in the SLb when thermal (25°C or 15°C) and light (continuous illumination or darkness) conditions are altered and following brain surgery that induces diapause or non-diapause eggs in the progeny. We have also examined the immunoreactivity of the other FXPRLa peptides by using anti-β-SGNP and anti-PBAN antibodies. Pupal SLb somata immunoreactivities seem to be affected by both thermal and light conditions during embryogenesis. Thus, we have been able to identify a close correlation between the immunoreactive intensity of neuropeptides and environmental conditions relating to the determination of embryonic diapause in B. mori.

Proteomic and bioinformatic analysis on endocrine organs of domesticated silkworm, Bombyx mori L. for a comprehensive understanding of their roles and relations

Three organs of silkworm larva endocrine system, including brain (Br), subesophageal ganglion (SG) and prothoracic glands (PG), were studied employing shotgun LC-MS/MS combined with bioinformatic analysis to comprehensively understand their roles and relations. Totally, 3430, 2683, and 3395 proteins were identified including 1885 common and 652, 253, and 790 organ-specific ones in Br, SG, and PG, respectively. Identified common-expressed proteins indicated the existence of intrinsic complex interactions among these parts of endocrine system. Most of the reputed organs-specific proteins were identified by this approach. KEGG pathway analysis showed 162 same pathways among the 169, 164, and 171 relating Br, SG, and PG. This analysis revealed functional similarities with exceptional resemblance in their metabolism and signaling pathways of the three organs. On the other hand, 70, 57, and 114 organ-specific enzymes related pathways were detected for Br, SG, and PG confirming their functional differences. These results reveal a cooperative mechanism among the three endocrine organs in regulating various physiological and developmental events, and also suggest that the organ-specific proteins might be the fundamental factors responsible for the functional differentiation of these organs.

Novel gene encoding precursor protein consisting of possible several neuropeptides expressed in brain and frontal ganglion of the silkworm, Bombyx mori

A novel gene (BmK5) expressed in the central nervous system of the silkworm, Bombyx mori, was isolated using a cDNA subtraction method. BmK5 was first cloned as a candidate regulator of diapause hormone release from subesophageal ganglion via corpus cardiacum-corpus allatum into the hemolymph; however, subsequent analyses revealed that the gene expression patterns in brain-subesophageal ganglion complexes did not differ between diapause and nondiapause egg producers. The deduced amino acid sequence showed the characteristics of secretory protein precursor or nuclear localization protein. Immunohistochemical experiments with an anti-BmK5 antibody revealed that BmK5 precursor protein exists in the cytoplasm of specific cells of brain and frontal ganglion, but not in the nuclei. In addition, a peptide (GSGTKVGGAGAATKVVTKSGS-NH(2)) possibly processed from the BmK5 precursor protein was immunohistochemically detected in the axons connecting the anti-BmK5 antibody-positive cells to the neurohemal organ, corpus cardiacum-corpus allatum. These results suggest that BmK5 encodes a precursor of the novel neurosecretory protein and that several mature peptides are released into the hemolymph via the corpus cardiacum-corpus allatum, although the functions of these peptides are yet unclear.

Molecular cloning and characterization of Bombyx mori CREB gene

The cAMP response element binding protein (CREB), as one of the best characterized stimulus-induced transcription factors, plays critical roles in activating transcription of target genes in response to a variety of environmental stimuli. To characterize this important molecule in the silkworm, Bombyx mori, we cloned a full-length cDNA of CREB gene from B. mori brains by using RACE-PCR. The sequence of B. mori CREB (named BmCREB1) gene contains a 88 bp 5' UTR, a 783 bp open reading frame (ORF) encoding 261 amino acids and a 348 bp 3' UTR. The deduced BmCREB amino acid sequence has 56.7% and 37.2% homology with CREB from Apis mellifera carnica and Drosophila melanogaster, respectively. The primary structure of the deduced BmCREB1 protein contains a kinase-inducible domain (KID) and a basic region/leucine zipper (bZIP) dimerization domain which exists in all CREB family members. Genomic analysis showed there are 9 exons and 5 introns in B. mori CREB genome sequences. We identified three different isoforms of BmCREB (BmCREB1, BmCREB2 and BmCREB3) through alternative splicing in C terminal. In addition, the expression of BmCREB in different developmental stages was investigated by using quantitative real-time PCR in both diapause and non-diapause type of B. mori bivoltine race (Dazao). BmCREB transcripts showed two peaks in embryonic stage and pupal stage in both types of bivoltine race. However, consistently higher expression of BmCREB was found throughout the developmental stages in the diapause type than in the non-diapause type. These results suggest that BmCREB is involved in the process of diapause induced by environmental factors.

Molecular cloning and characterization of cDNAs encoding dopamine receptor-1 and -2 from brain-suboesophageal ganglion of the silkworm, Bombyx mori

In order to better understand the relationship between dopamine and the release of diapause hormone into the blood, we cloned and characterized cDNAs encoding Bombyx mori dopamine receptor-1 and -2 (BmDopR1 and 2) from the pupal brain-suboesophageal ganglion. BmDopR1 and 2 had high similarities to group 1 (Drosophila melanogaster DOP1 and Apis mellifera DOP1) and group 2 (D. melanogaster DopR99B, A. mellifera DOP2 and Papilio xuthus DOP1), respectively. When BmDopR1 and 2 were expressed in human embryonic kidney (HEK) cells, they responded to dopamine by increasing intracellular cAMP levels, thus indicating the presence of D1-like receptors. There were no clear differences in BmDopR1 and 2 mRNA levels between brain-suboesophageal ganglion complexes of diapause and nondiapause egg producers during pupal-adult development. BmDopR1 and 2 mRNAs were concentrated in the mushroom body calyx rather than in the suboesophageal ganglion. Taking into account the results of earlier experiments on excised regions corresponding to mushroom bodies, BmDopR1 and 2 in the mushroom body apparently play a role in the release of diapause hormone.

Neuroanatomical approaches to the study of insect photoperiodism

The anatomical locations of three components of insect photoperiodism--the photoperiodic photoreceptor, photoperiodic clock and hormonal effector--are summarized and compared between species. Among photoperiodic photoreceptors, either the retinal or extraretinal types or both are operative, and there is no general relationship between phylogeny and photoreceptor type. The photoperiodic clock comprises time measurement and counter systems. Currently, it is generally accepted that circadian oscillators are involved in the photoperiodic clock. Several recent studies have raised the possibility that timeless, a circadian clock gene, plays a role in the photoperiodic clock in flies. The dorsal protocerebrum has been identified as an important region regulating the endocrine system for adult, pupal and embryonic diapause controlled by photoperiod. In the blow fly Protophormia terraenovae, neural connections between circadian clock neurons and indispensable neurons in the pars lateralis for diapause induction in the dorsal protocerebrum have been demonstrated. This neural network may provide the access needed to investigate the neural components of the photoperiodic clock.

FXPRL-amide peptides induce ecdysteroidogenesis through a G-protein coupled receptor expressed in the prothoracic gland of Bombyx mori

The FXPRL-amide peptide family (pyrokinin/PBAN family) consists of insect peptides that function broadly in insect life processes and are characterized by a conserved C-terminal motif. In the silkworm, Bombyx mori, sex pheromone biosynthesis and induction of embryonic diapause are regulated by peptides from this family. To elucidate other functions of Bombyx FXPRL-amide peptides, we analyzed the tissue expression patterns of two known Bombyx G-protein coupled receptors for these peptides. We found that the Bombyx diapause hormone receptor (BmDHR), is expressed in the prothoracic gland (PG), the organ which synthesizes and releases the insect molting hormones, ecdysteroids. Furthermore, diapause hormone (DH), a member of the Bombyx FXPRL-amide peptides, increases both intracellular Ca(2+) and cAMP concentrations and induces ecdysteroidogenesis in late fifth instar PGs coincident with BmDHR expression in the PGs. DH also has the highest prothoracicotropic activity among the FXPRL-amide peptides, which corresponds well to the ligand specificity of heterologously expressed BmDHR. These results demonstrate that FXPRL-amide peptides can function as prothoracicotropic factors through the activation of BmDHR and may play an important role in controlling molting and metamorphosis.

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.

Molecular properties and tissue distribution of 30K proteins as ommin-binding proteins from diapause eggs of the silkworm, Bombyx mori

We previously reported the purification of an ommin-binding protein (OMBP) from an acid-methanol extract of diapause eggs of the silkworm and that OMBP reacted with the anti-30K proteins antiserum. In order to clarify the relationship between OMBP and the 30K proteins, we attempted to determine the sequence of the N-terminal amino acid of OMBP, which was separated by two-dimensional polyacrylamide gel electrophoresis (2D-PAGE). We observed ten protein spots of various isoelectric points; the spots corresponded with 30 kDa. Based on the sequence of the N-terminal amino acid (20 residues), the spots belonged to two kinds of 30K proteins (6G1 and 19G1), which are known as the major plasma proteins in the larval hemolymph of the silkworm. The proteins are expected to attach to polysaccharide because they reacted with concanavalin A and elderberry bark lectin. Immunohistochemical observations clarified that the proteins were localized in yolk granules and serosa in the diapause egg. These results suggest that OMBP is composed of 30K proteins which were modified with polysaccharides. In addition, the expression of 30K proteins mRNA was observed at early embryonic stage in diapause eggs by RT-PCR analysis. The 30K proteins as OMBP may play an important role in the transport and accumulation of tryptophan metabolites and ommochrome during the formation of serosa.

G protein-coupled receptor for diapause hormone, an inducer of Bombyx embryonic diapause

Bombyx diapause hormone was the first chemical substance identified as a maternal control factor that arrests offspring development. However, the molecular mechanisms by which the hormone transduces the signal to the oocyte that induces embryonic diapause immediately after mesoderm segmentation are not fully understood. Here, we describe a cDNA for a G protein-coupled diapause hormone receptor with seven transmembrane domains. Its amino-acid sequence shows a high level of similarity to the receptors of mammalian neuromedin U and insect regulatory peptide, an FXPRL-amide C-terminus. When expressed in a Xenopus oocyte system, the receptor exhibited the highest affinity (EC(50), approximately 70nM) for diapause hormone, when compared with other Bombyx FXPR/KL-amide peptides. Diapause hormone without amidation at the C-terminus, which never induces embryonic diapause in vivo, had no effect in this heterologous expression system. The mRNA is expressed in the ovaries during Bombyx pupal-adult development. These results strongly indicate that the cDNA encodes the diapause hormone receptor.