Cloning of a Gene Encoding Bombyxin, an Insulin-Like Brain Secretory Peptide of the Silkmoth Bombyx mori with Prothoracicotropic Activity. (Bombyx mori/brain peptide/bombyxin/insulin/IGF)

Identification, Synthesis, Conformation and Activity of an Insulin-like Peptide from a Sea Anemone

The role of insulin and insulin-like peptides (ILPs) in vertebrate animals is well studied. Numerous ILPs are also found in invertebrates, although there is uncertainty as to the function and role of many of these peptides. We have identified transcripts with similarity to the insulin family in the tentacle transcriptomes of the sea anemone Oulactis sp. (Actiniaria: Actiniidae). The translated transcripts showed that these insulin-like peptides have highly conserved A- and B-chains among individuals of this species, as well as other Anthozoa. An Oulactis sp. ILP sequence (IlO1_i1) was synthesized using Fmoc solid-phase peptide synthesis of the individual chains, followed by regioselective disulfide bond formation of the intra-A and two interchain disulfide bonds. Bioactivity studies of IlO1_i1 were conducted on human insulin and insulin-like growth factor receptors, and on voltage-gated potassium, sodium, and calcium channels. IlO1_i1 did not bind to the insulin or insulin-like growth factor receptors, but showed weak activity against KV1.2, 1.3, 3.1, and 11.1 (hERG) channels, as well as NaV1.4 channels. Further functional studies are required to determine the role of this peptide in the sea anemone.

DNA synthesis during endomitosis is stimulated by insulin via the PI3K/Akt and TOR signaling pathways in the silk gland cells of Bombyx mori

Silk gland cells undergo multiple endomitotic cell cycles during silkworm larval ontogeny. Our previous study demonstrated that feeding is required for continued endomitosis in the silk gland cells of silkworm larvae. Furthermore, the insulin signaling pathway is closely related to nutritional signals. To investigate whether the insulin signaling pathway is involved in endomitosis in silk gland cells, in this study, we initially analyzed the effects of bovine insulin on DNA synthesis in endomitotic silk gland cells using 5-bromo-2'-deoxyuridine (BrdU) labeling technology, and found that bovine insulin can stimulate DNA synthesis. Insulin signal transduction is mainly mediated via phosphoinositide 3-kinase (PI3K)/Akt, the target of rapamycin (TOR) and the extracellular signal-regulated kinase (ERK) pathways in vertebrates. We ascertained that these three pathways are involved in DNA synthesis in endomitotic silk gland cells using specific inhibitors against each pathway. Moreover, we investigated whether these three pathways are involved in insulin-stimulated DNA synthesis in endomitotic silk gland cells, and found that the PI3K/Akt and TOR pathways, but not the ERK pathway, are involved in this process. These results provide an important theoretical foundation for the further investigations of the mechanism underlying efficient endomitosis in silk gland cells.

Identification of novel bombyxin genes from the genome of the silkmoth Bombyx mori and analysis of their expression

Insulin family peptide members play key roles in regulating growth, metabolism, and reproduction. Bombyxin is an insulin-related peptide of the silkmoth Bombyx mori. We analyzed the full genome of B. mori and identified five novel bombyxin families, V to Z. We characterized the genomic organization and chromosomal location of the novel bombyxin family genes. In contrast to previously identified bombyxin genes, bombyxin-V and -Z genes had intervening introns at almost the same positions as vertebrate insulin genes. We performed reverse transcription-polymerase chain reaction and in situ hybridization in different tissues and developmental stages to observe their temporal and spatial expression patterns. The newly identified bombyxin genes were expressed in diverse tissues: bombyxin-V, -W, and -Y mRNAs were expressed in the brain and bombyxin-X mRNA in fat bodies. Bombyxin-Y gene was expressed in both brain and ovary of larval stages. High level of bombyxin-Z gene expression in the follicular cells may suggest its function in reproduction. The presence of a short C-peptide domain and an extended A chain domain, and high expression of bombyxin-X gene in the fat body cells during non-feeding stages suggest its insulin-like growth factor-like function. These results suggest that the bombyxin genes originated from a common ancestral gene, similar to the vertebrate insulin gene, and evolved into a diverse gene family with multiple functions.

Synganglion transcriptome and developmental global gene expression in adult females of the American dog tick, Dermacentor variabilis (Acari: Ixodidae)

454 Pyrosequencing was used to characterize the expressed genes from the synganglion and associated neurosecretory organs of unfed and partially fed virgin and mated replete females of the American dog tick, Dermacentor variabilis. A total of 14,881 contiguous sequences (contigs) was assembled, with an average size of 229 bp. Gene ontology terms for Level 2 biological processes were assigned to 4366 contigs. Seven acetylcholinesterases, a muscarinic acetylcholine (ACh) receptor, two nicotinic ACh receptor β-subunits, two ACh unc-18 regulators, two dopamine receptors, two gamma aminobutyric acid (GABA) receptors, two GABA transporters, two norepinephrine transporters and an octopamine receptor are described. Microarrays were conducted to examine global gene expression and quantitative real-time polymerase chain reaction was used to verify expression of selected neuropeptides. Hierarchical clustering of all differentially expressed transcripts grouped part-fed and replete ticks as being more similar in terms of differentially expressed genes with unfed ticks as the outgroup. Nine putative neuropeptides (allatostatin, bursicon-β, preprocorazonin, glycoprotein hormone α, insulin-like peptide, three orcokinins, preprosulphakinin) and a gonadotropin releasing hormone receptor were differentially expressed, and their developmental expression and role in reproduction was investigated. The presence of eclosion hormone, corazonin and bursicon in the synganglion, which in insects regulate behaviour and cuticle development associated with moulting, suggest that this system may be used in ticks to regulate blood feeding, cuticle expansion and development related to female reproduction; adult ticks do not moult.

Production of a recombinant antibody fragment in whole insect larvae

Infection of insect cells with baculovirus expression constructs is commonly used to produce recombinant proteins that require post-translational modifications for their activity, such as mammalian proteins. However, technical restraints limit the capacity of insect cell-based culture systems to be scaled up to produce the large amounts of recombinant protein required for human pharmaceuticals. In this study, we designed an automated insect rearing system and whole insect baculovirus expression system (PERLXpress) for the expression and purification of recombinant proteins on a large scale. As a test model, we produced a recombinant mouse anti-botulinum antibody fragment (Fab) in Trichoplusia ni larvae. A recombinant baculovirus co-expressing the Fab heavy and light chains together with N-terminal sequences from the silkworm hormone bombyxin, to direct proteins into the secretory pathway, was constructed. Fifth instar larvae were reared and infected orally with recombinant (pre- occluded) baculovirus using the automated system and harvested approximately after 4 days. The total yield of recombinant Fab was 1.1 g/kg of larvae, resulting in 127 mg of pure Fab in one production run. The Fab was purified to homogeneity using immobilized metal affinity chromatography, gel filtration, and anion exchange chromatography. The identity of the purified protein was verified by Western blots and size-exclusion chromatography. Purified recombinant Fab was used to detect botulinum toxin in ELISA experiments, demonstrating that the heavy and light chains were properly assembled and folded into functional heterodimers. We believe that this is the first demonstration of the expression of a recombinant antibody in whole insect larvae. Our results demonstrate that a baculovirus-whole larvae expression system can be used to express functionally active recombinant Fab fragments. As the PERLXpress system is an automated and linearly scalable technology, it represents an attractive alternative to insect cell culture for the production of large amounts of human pharmaceuticals.

Hormonal control of tick development and reproduction

Ecdysteroids (moulting hormones), juvenoids and neuropeptides in ticks are reviewed but, by far, the emphasis is on the former since this class of hormones has been the subject of most investigations. In immature stages of ticks, ecdysteroids have been shown to regulate moulting and to terminate larval diapause. Although there is a paucity of information on the molecular action of ecdysteroids in ticks, their action appears to be via a heterodimeric ecdysone/ultraspiracle receptor, as in insects. The role of ecdysteroids in sperm maturation in adult males is considered. In females, ecdysteroids function in the regulation of salivary glands, of production of sex pheromones and of oogenesis and oviposition. There is evidence for ecdysteroid production in the integument and pathways of hormone inactivation are similar to those in insects. Ecdysteroids also function in embryogenesis. Although evidence for the occurrence and functioning of juvenile hormones in ticks has been contradictory, in recent thorough work it has not been possible to detect known juvenile hormones in ticks, nor to demonstrate effects of extracts on insects. Factors (neuropeptides) from the synganglion affect physiological processes and limited immunocytochemical studies are reviewed. Sigificantly, a G-protein-coupled receptor has been cloned, expressed, and specifically responds to myokinins.

Effects of 20-hydroxyecdysone and other hormones on egg development, and identification of a vitellin-binding protein in the ovary of the tick, Amblyomma hebraeum

Partially fed adult female Amblyomma hebraeum ticks were injected with 20-hydroxyecdysone (20E; up to 43 microg/g body weight (bw)), juvenile hormone III (JH III; up to 100 microg/g bw), bovine insulin (up to 2000 mU/g bw), or triiodothyronine (up to 200 ng/g bw) in an attempt to stimulate vitellogenesis. Of these, only 20E stimulated synthesis and release of vitellogenin (Vg). Immunoblot analysis revealed that Vg-synthesis occurred in the fat body. However, consistent with earlier observations suggesting that a distinct signal may be required for Vg-uptake, there was no significant Vg-uptake by oocytes of partially fed, 20E-treated ticks. Because Vg-uptake commonly occurs via receptor-mediated endocytosis (i.e., a specific Vg-receptor), we attempted to identify a vitellin (Vt)-binding protein in ovaries of engorged female ticks. A single 86 kDa Vt-binding protein was identified, even under reducing conditions (2-mercaptoethanol), by a ligand-blotting technique. Sodium salt of suramin (5 mM) inhibited binding of Vt to the 86 kDa protein. However, this protein was also detected in ovaries from small partially fed ticks (50-100 mg), suggesting that the inability of 20E to stimulate Vg-uptake in partially fed ticks may not have been due to the absence of a Vg-receptor.

Insulin-like system and growth regulation in the Pacific oyster Crassostrea gigas: hrIGF-1 effect on protein synthesis of mantle edge cells and expression of an homologous insulin receptor-related receptor

The involvement of molecules belonging to the insulin/IGF family in regulation of growth has been investigated in the Pacific oyster Crassostrea gigas. In vitro biological effects of human recombinant IGF-1 (hrIGF-1) on mantle edge cells, involved in oyster shell and soft body growth, were studied over an annual cycle. In mantle edge cells hrIGF-1 stimulates protein synthesis of 56+/-5.1% over basal for 10(-10) M in September with in addition a clear dose-effect corresponding to the highest shell growth period, and 57.5+/-3.45% over basal for 10(-11) M in March and 51+/-5.4% over basal for 10(-10) M in April corresponding to the period of mantle growth. These insulin-like effects were associated with the expression of a recently identified C. gigas insulin receptor-related receptor (CIR) in mantle edge cells as demonstrated by RT-PCR. Moreover, in situ hybridisation (ISH) confirmed this expression at the level of the inner and outer epithelia involved in mantle growth and shell formation.

Antipeptide antibodies for detecting crab (Callinectes sapidus) molt-inhibiting hormone

In crustaceans, the synthesis of ecdysteroid molting hormones is regulated by molt-inhibiting hormone (MIH), a neuropeptide produced by an eyestalk neuroendocrine system, the X-organ/sinus gland complex. Using sequence analysis software, two regions of the blue crab (Callinectes sapidus) MIH peptide were selected for antibody production. Two 14-mer peptides were commercially synthesized and used to generate polyclonal antisera. Western blot analysis revealed that each antiserum bound to proteins of the predicted size in extracts of C. sapidus sinus glands, and lysates of insect cells containing recombinant MIH. Thin section immunocytochemistry using either antiserum showed specific immunoreactivity in X-organ neurosecretory cell bodies, their associated axons and collaterals, and their axon terminals in the sinus gland.

Insulin-related peptides and their conserved signal transduction pathway

The 'insulin superfamily' is an ancient category of small, structurally related proteins, such as insulin, insulin-like growth factors (IGF) and relaxin. Insulin-like signaling molecules have also been described in different invertebrates, including nematodes, mollusks, and insects. They initiate an evolutionary conserved signal transduction mechanism by binding to a heterotetrameric, membrane-spanning receptor tyrosine kinase. Recent physiological and genetic studies have revealed that, in different metazoans, the insulin signaling pathway plays a pivotal role in the regulation of a variety of interrelated, fundamental processes, such as metabolism, growth, reproduction and aging.

Platelet-derived growth factor and transforming growth factor-beta in invertebrate immune and neuroendocrine interactions: another sign of conservation in evolution

Growth factor-like molecules have been found in various invertebrate species. In particular, we have reported the presence of platelet-derived growth factor (PDGF)-AB and transforming growth factor-beta (TGF-beta)1 immunoreactive molecules in molluscs, insects and annelids. Moreover, PDGF-AB and TGF-beta1 affect the main immune functions, such as phagocytosis, chemotaxis and cell motility. Changes in cell shape are induced via interactions of growth factors with their respective specific receptors. The extracellular signals are transduced by the activation of classical signal transduction pathways, such as those involving PKA and PKC, and pivotal transcription regulators, i.e. the Fos, Jun and SMAD proteins. The two growth factors intervene in stress responses by activating the CRH-ACTH-biogenic amine axis. Exogenous administration of PDGF-AB and TGF-beta1 in a molluscan wound provokes an accelerated migration of immunocytes and fibroblasts to the injured area, stimulating granulation tissue formation and wound re-epithelialization. These findings suggest that these molecules are ancestral and that their function is well conserved and crucial in the maintenance of invertebrate homeostasis.

Prothoracicotropic activity of SBRPs, the insulin-like peptides of the saturniid silkworm Samia cynthia ricini

Synthesis and secretion of the insect molting hormone ecdysteroid in the prothoracic glands (PGs) are stimulated by the prothoracicotropic hormone (PTTH) secreted by the brain. Bombyxins, insulin-like peptides of the silkworm Bombyx mori, show prothoracicotropic activity when administered to the saturniid silkworm Samia cynthia ricini, but they are inactive to B. mori itself. Recently, the genes for the bombyxin homologs of S. cynthia ricini (referred to as Samia bombyxin-related peptides, SBRPs) were cloned. To examine the prothoracicotropic activity of SBRPs on S. cynthia ricini, we synthesized two representative molecules, SBRP-A1 and -B1. They promoted pupa-to-adult development with ED(50) of 50 and 10 ng/pupa (EC(50) of 5 and 1 nM), respectively.

Bombyxin F1 gene: structure and expression of a new bombyxin family gene that forms a pair with bombyxin B10 gene

Bombyxin F1 gene, a new bombyxin family gene, has been identified. The F1 gene forms a pair with bombyxin B10 gene with an opposite transcriptional orientation and the gene pair F1/B10 is located between bombyxin gene pairs B9/C1 and A7/B7 in a bombyxin gene cluster. The nucleotide sequence of the F1 gene and its deduced amino acid sequence deviate moderately from those characterized previously for the family-A, family-B, family-C, family-D, and family-E bombyxin genes; the bombyxin F1 gene and preprobombyxin F1 share no more than 62% and 53% sequence identities with other bombyxin members, respectively. Harr-plot analysis indicated that the spacer of the F1/B10 gene pair has low sequence similarity with that of other bombyxin gene pairs characterized. The bombyxin F1 mRNA in Bombyx mori brain was shown to locate in four pairs of medial neurosecretory cells, which also produce other bombyxin family mRNAs. Genomic Southern hybridization indicated that the Bombyx haploid genome contains a single copy of the family-F bombyxin gene.

Structure and expression of bombyxin E1 gene: a novel family gene that encodes bombyxin-IV, an insect insulin-related neurosecretory peptide

A bombyxin gene encoding precursor molecule for bombyxin-IV, one of the insulin-related neurosecretory peptide of the silkmoth Bombyx mori, has been cloned and characterized. The nucleotide sequence of this gene and its deduced amino acid sequence deviate moderately from those characterized previously for the family A, B, C and D bombyxin genes. The gene encoding the bombyxin-IV precursor was therefore defined into a novel family E and designated as gene E1. The bombyxin E1 transcript in Bombyx brain was shown to locate in four pairs of medial neurosecretory cells, which also produce other bombyxin family mRNAs, and the amount of the E1 transcript did not change markedly during the fifth larval instar. Genomic Southern hybridization indicated that the Bombyx haploid genome contained a single copy of the bombyxin family E gene.

A novel neuropeptide-endocrine interaction controlling ecdysteroid production in ixodid ticks

Ixodid (hard) ticks are blood-feeding arthropods that require a blood meal to complete each stage of development. However, the hormonal events coordinating aspects of feeding and development are only poorly understood. We have delineated a new neuropeptide-endocrine interaction in the adult tick, Amblyomma hebraeum, that stimulates the synthesis of the moulting hormones, the ecdysteroids. In adult female ticks, ecdysteroid synthesis could be demonstrated in integumental tissue incubated in vitro with a synganglial (central nervous system) extract, but not in its absence. Stimulation by the synganglial extract is both time- and dose-dependent, but is completely abolished by trypsin treatment, suggesting that the activity is due to a peptide/protein. Integumental tissue ecdysteroidogenesis is also stimulated by elevation of the cAMP concentration using forskolin and 3-isobutyl-l-methyl-xanthine, or by 8-bromo-cAMP. This suggests the involvement of at least a cAMP second messenger system in the neuropeptide-ecdysteroidogenesis axis, without precluding a role for other second messengers as well. Despite involving a quite different steroidogenic tissue, the foregoing system has some parallels with the known prothoracicotropic hormone (neuropeptide)-prothoracic gland endocrine axis of insects.

The effects of insulin/IGF-I on glucose and leucine metabolism in the redclaw crayfish (Cherax quadricarinatus)

In recent years, invertebrate peptides have been identified which share substantial homologies with vertebrate insulin and insulin-like growth factors (IGFs), indicating a high degree of conservation of insulin/IGF systems through animal evolution. In a previous study, we provided evidence for the presence of IGF-I-like peptides in the redclaw (Cherax quadricarinatus), a species of freshwater crayfish endemic to northern Australia river systems which has attained support as a culture species. The general aim of the current study was to elucidate the functional significance of IGF-I-like peptides in this species by examining the effects of mammalian IGF-I on glucose and leucine metabolism. Juvenile redclaw were injected with a single dose of purified human insulin, recombinant human (rh) IGF-I, or Des-1-3-IGF-I. Glucose levels in redclaw tissues were then determined over an 8-hr period using enzymatic approaches. It was shown that injection of rhIGF-I induced an acute increase in free glucose content in hepatopancreas while Des-1-3-IGF-I and insulin raised free glucose levels in abdominal muscle. Radiolabel tracer approaches also demonstrated that injection of rhIGF-I increased glycogen synthesis in abdominal muscle and elevated the incorporation of leucine into protein in both abdominal muscle and hepatopancreas. Taken together, the findings of this study suggest that IGF-I-like peptides are biologically active in this species and may be of significance to metabolic and growth-related processes.

Insulin receptor-like tyrosine kinase in the tobacco hornworm, Manduca sexta

Phosphotyrosine-containing proteins are present in the prothoracic glands, muscle, and fat body of Manduca sexta, as determined by immunoprecipitation followed by kinase assay, and by Western blotting. One such protein (M(r) 178,000) can also be immunoprecipitated using antibodies directed against the human insulin receptor and insulin receptor substrate. The 178 kD protein appears to be expressed more strongly in prothoracic glands removed just prior to wandering (days 3-4) and prior to pupation (days 7-9), and phosphorylation of the protein is enhanced by an M. sexta brain factor. The results suggest that a tyrosine-kinase-linked molecule similar to the insulin receptor may play a regulatory role in M. sexta.

Bombyxin gene expression in tissues other than brain detected by reverse transcription-polymerase chain reaction (RT-PCR) and in situ hybridization

Bombyxin is a 5 kDa insulin-related peptide produced in four pairs of medial neurosecretory cells in the brain of the silkmoth Bombyx mori. We demonstrate here the presence of bombyxin mRNA in tissues other than brain: ganglia, epidermis, testis, ovary, fat body, silk gland, Malpighian tubule, midgut, and hindgut of the Bombyx fifth instar larvae. Bombyxin mRNA was detected by Oligotex reverse transcription-polymerase chain reaction (RT-PCR), a rapid and simple procedure of reverse transcription-PCR, and in situ hybridization. The Oligotex RT-PCR method effectively eliminated the contaminating DNA in RNA samples and amplified bombyxin mRNA efficiently. In situ hybridization of the Bombyx ovary clearly demonstrated the localization of the bombyxin mRNA in the ovariole. The present study is the first demonstration of expression of brain neurosecretory peptide in tissues other than the central nervous system in insects at RNA level.

Bombyxin-related peptides: cDNA structure and expression in the brain of the hornworm Agrius convolvuli [corrected]

We have cloned three cDNAs from the sweet potato hornworm Agrius convolvuli that encode precursor molecules for peptides structurally related to bombyxin, an insulin-related brain secretory peptide in Bombyx mori. The Agrius bombyxin-related peptide (ABRP) cDNAs are classified into type A and B according to their sequence similarity. The prepro-ABRPs deduced from the cDNA sequences have the insulin-like domain organization of signal peptide/B chain/C peptide/A chain. The ABRP transcripts in Agrius brain were shown to locate in four pairs of medial neurosecretory cells, the homologous group of neurosecretory cells that produce bombyxins in Bombyx brain. Genomic Southern analysis indicated the presence of multiple copies of ABRP gene in the Agrius genome. Results showed that the ABRP genes are remarkably different from the vertebrate insulin genes in the number of copy and spatial localization of the transcripts.

Insect prothoracicotropic hormone: a new member of the vertebrate growth factor superfamily

Prothoracicotropic hormone (PTTH) is a brain neurosecretory protein that controls insect development. PTTH of the silkmoth Bombyx mori is a homodimeric protein, the subunit of which consists of 109 amino acids. Clear-cut sequence similarity to any other proteins has not been observed. By disulfide-bond pattern analysis and modeling of the PTTH structure based on the known three-dimensional (3D) structures of growth factor family with cystine-knot motif, we propose that the PTTH protomer adopts the fold unique to the structural superfamily of the growth factors, beta-nerve growth factor (beta-NGF), transforming growth factor-beta 2 (TGF-beta 2), and platelet-derived growth factor-BB (PDGF-BB). The insect neurohormone PTTH appears to be a member of the growth factor superfamily, sharing a common ancestral gene with the three vertebrate growth factors, beta-NGF, TGF-beta 2 and PDGF-BB.

Comparative aspects of peptidergic signaling pathways in the nervous systems of arthropods

Comparative aspects of arthropod peptidergic systems--in principle--can be studied on the level of precursor sequences (genes, preprohormones), peptide sequences (peptide families), and peptide expression patterns within the nervous system. The number of known arthropod neuropeptide precursor sequences is as yet far too small to provide a reasonably large basis for extended comparative studies. Comparative studies of peptide sequences have shown that many peptides belong to families with homologous members in both invertebrates and vertebrates. Comparative research on peptide expression has to find out whether phylogenetic necessities lead to "hard wired" neurochemical identities, i.e., a more or less fixed "Bauplan" that not only determines the lineage and morphology of a neuron but also its transmitter(s), or whether these necessities demand greater flexibility (plasticity), and hence cause great variability that would complicate comparative studies. As will be shown here, both possibilities appear to exist. On the one hand, peptidergic neurons may exist in comparable form in different groups of arthropods. On the other hand, the neurochemical identity of cells may vary in segmented organisms when comparing serially homologous sets of nerve cells in different segments. As a further complication, identical or similar peptides may serve different functions, even in closely related species. In view of these functional aspects in particular, it appears that peptidergic signalling pathways represent rapidly evolving systems. This conclusion, although very interesting in itself, reduces the use of such systems for general comparisons. However, arthropod nervous systems represent excellent model systems for the study of homology. At least for morphological and ontogenetic aspects arthropods provide numerous opportunities to study homology on the level of the individually identified peptidergic nerve cell.

Identification of insulin-like peptides in cerebral ganglia neurosecretory cells of the mussel Mytilus edulis

The immunostaining patterns of cerebral ganglia sections from the mussel Mytilus edulis with monoclonal antibodies raised against cerebral ganglia (CG) extracts were compared to those obtained with various polyclonal anti-insulin-like antibodies. One of the monoclonal antibodies (MAB 46) revealed clusters of positive cells in localization comparable to those revealed by the polyclonal antibodies. The nature of the antigen recognized by MAB 46 and the polyclonal antibodies was compared by gel filtration-HPLC of a cerebral ganglia extract. Similar peaks were revealed by the monoclonal and polyclonal antibodies. MAB 46 significantly inhibited the cerebral ganglia induced stimulation of amino-acid incorporation by mantle edge cell suspensions, suggesting that the antigen recognized by MAB 46 is involved in the control of growth.

Seripauperins of Saccharomyces cerevisiae: a new multigene family encoding serine-poor relatives of serine-rich proteins

A gene, PAU1, has been cloned from Saccharomyces cerevisiae and sequenced. It is located in a telomeric region, probably on chromosome IV, and contains an open reading frame encoding a protein of 120 amino acids (aa) (approx. 13 kDa). The deduced sequence is nearly identical to two other genes found in GenBank (named PAU2 and PAU3 by us), which are located close to the ends of chromosomes V and III, respectively. Blotting of separated chromosomes with a PAU1 probe at high stringency revealed that at least six chromosomes in addition to III, IV and V possessed related sequences, suggesting a large gene family. Probing of an ordered array of phage lambda clones containing yeast genomic DNA inserts ('Olson filters') revealed ten additional hybridizing sequences, located close to the ends of the left and/or right arms of chromosomes I, II, VII, VIII, X, XII, XIV and XV. Transcription of these sequences could not be demonstrated, however, under a wide variety of growth and culture conditions. The deduced PAU1, PAU2 and PAU3 aa sequences are all highly homologous with the SRP1 aa sequences, which contains eight serine-rich tandem repeats of 12 aa each, at its C terminus. This homology is limited, however, to the N-terminal half of SRP1, and does not include the repeats. In fact, PAU1 is quite serine-poor (5.8%), leading to the suggested name of seripauperins for this family of genes.

The prothoracicotropic hormone (PTTH) of the commercial silkmoth, Bombyx mori, in the CNS of the tobacco hornworm, Manduca sexta

Immunocytochemistry revealed that a Bombyx mori prothoracicotropic hormone (PTTH)-like peptide is expressed by the Manduca sexta big PTTH-producing neurons, the lateral neurosecretory cell group III (L-NSC III). Independent PCR of genomic DNA and a L-NSC III cDNA library yielded products with 99% sequence similarity to the cDNA encoding Bombyx PTTH. This similarity necessitated evaluation of the relationship between Manduca big PTTH and Bombyx PTTH by 1) bioassay of IEF separated Manduca PTTH and 2) direct assessment of Bombyx PTTH biological activity with Manduca prothoracic glands. Together, these studies indicate that Bombyx PTTH and Manduca PTTH are different peptides expressed by the L-NSC III. The possible physiological significance of a Bombyx PTTH-like peptide in Manduca and its coexpression with Manduca big PTTH by the L-NSC III are discussed.

Recent advances in insect neuropeptides

1. The number of insect neuropeptides identified chemically grows rapidly and most important neuropeptides have already been characterized. After multi-year efforts Bombyx diapause hormone has recently been isolated and sequenced. 2. New approaches to search for new insect neuropeptides have been carried out by two groups of workers, which have succeeded in identifying several unique peptides. 3. cDNAs for more than 10 insect neuropeptides have been cloned and sequenced. It was found that two functionally distinct neuropeptides, Bombyx diapause hormone and pheromone biosynthesis activating neuropeptide, are encoded in a single gene.

Phylogeny of the insulin-like growth factors (IGFs) and receptors: a molecular approach

The IGFs (IGF-I and IGF-II) are essential for normal mammalian growth and development. Their actions are mediated primarily by their interactions with the type I IGF receptor (IGF-I receptor), a transmembrane tyrosine kinase. The ligands and the IGF-I receptor are structurally related to insulin and to the insulin receptor, respectively. Analysis of evolutionary conservation has often provided insights into essential regions of molecules such as hormones and their receptors. The genes for insulin and IGFs have been partially characterized in a number of vertebrate species extending evolutionarily from humans as far back as fish. The sequences of the exons encoding the mature insulin and IGF peptides are highly conserved among vertebrate species, and IGF-I-like molecules are found in species whose origins extend back as much as 550 million years. The insulin receptor is also highly conserved in vertebrate species, and an insulin-receptor-like molecule has been characterized in Drosophila. In contrast, IGF-I receptors have only been characterized in mammalian species and partially studied in Xenopus, in which the tyrosine kinase domain is highly conserved. Studies are presently being undertaken to analyze in more detail the regulation of the genes encoding this important family of growth factors and the structure/function relationships in the gene products themselves.

The IGFs and their binding proteins in murine development

Recent observations suggest that the diverse actions of the insulin-like growth factors (IGFs) are the result of interactions of the various components that make up the IGF system. The components of this system include IGF-I and -II and their variants, the type 1 and 2 IGF receptors and the insulin-like growth factor binding proteins (IGFBPs). Various components of the IGF system are expressed in the developing mouse embryo and the adjacent tissues of the reproductive tract in which the embryo develops. Thus there is the potential for paracrine interactions between the maternal and fetal tissues. Transcripts for the IGF receptors, IGF-I and IGF-II, have been demonstrated in the periimplantation mouse embryo. While there are now data from gene ablation experiments indicating that IGF-II is important in embryogenesis, the role of other components of the IGF system such as the IGFBPs remains unclear. The data accumulated so far are largely empirical, and there is as yet little compelling evidence that maternal IGFs derived from oviduct or uterine fluid and maternal tissues are necessary for normal fetal development. We have started to develop transgenic mice lines overexpressing IGFBPs to attempt to address the role of these binding proteins in fetal development.

Immunoaffinity purification of the neuropeptide prothoracicotropic hormone from Manduca sexta

The prothoracicotropic hormones (PTTH) are cerebral peptides that control insect postembryonic development by stimulating the prothoracic glands to synthesize ecdysteroids. Using immunoaffinity chromatography and SDS-PAGE, a 25.5 kDa big PTTH has been purified from Manduca sexta. Based upon SDS-PAGE and Western blot analysis, the native form of big PTTH appears to be a dimer with monomers of 16.5 kDa. Four HPLC-separated fragments of this acidic peptide were sequenced and exhibited no sequence similarity with Bombyx mori PTTH. In agreement with this finding, the basic Bombyx PTTH had no PTTH bioactivity in Manduca. One sequenced fragment of the Manduca PTTH is approximately 70% similar to the vertebrate cellular retinoid binding proteins, suggesting these binding proteins may be present in insects.

Insect neuropeptides: discovery and application in insect management

New approaches to the development of insect control agents have been revealed through the molecular description of neuropeptides, their biogenesis, action, and degradation. Prerequisite to the exploitation of a neuropeptide as a lead to control agent development is a thorough understanding of the biochemistry of the neuropeptide and appreciation of its physiological impact. Reliable bioassays must be coupled with advanced biochemical and molecular genetic technologies to overcome limitations imposed by the typically low endogenous levels of individual neuropeptides. Purification, amino acid sequencing, and gene cloning provide the molecular tools necessary for studies on neuropeptide synthesis, processing, secretion, receptor binding, and inactivation. Each of these areas consists of a number of amino acid sequence-, and enzyme-dependent steps which may be considered as targets for the development of highly specific control agents. These agents will include antagonist and superagonists, peptidomimetics, recombinant peptides delivered through the baculovirus technology, receptor blockers, and enzyme inhibitors.

Neuropeptides of the silkworm, Bombyx mori

Six neuropeptides of the silkworm, Bombyx mori, have been isolated and chemically characterized during the past 10 years. They are bombyxin, prothoracicotropic hormone, pheromone-biosynthesis-activating neuropeptide/melanization-and-reddish-coloration hormone, diapause hormone, eclosion hormone, and adipokinetic hormone. Recent progress in research on these neuropeptides is described.

Structure and expression of bombyxin-related peptide genes of the moth Samia cynthia ricini

From the genomic DNA of the moth Samia cynthia ricini, we cloned and characterized six clustered genes that encode precursor molecules for peptides structurally related to bombyxin, a Bombyx mori brain secretory peptide that is structurally like insulin and functionally like the prothoracicotropic hormone. The precursor molecules deduced from these genes have the domain organization of signal peptide/B-chain/C-peptide/A-chain, as in preprobombyxins and preproinsulins. The Samia bombyxin-related peptide (SBRP) genes are classified into families A and B according to their sequence homology. Two genes belonging to different families are arranged close to each other to form a pair with opposite transcriptional orientations (A-1/B-1, A-2/B-2, and A-3/B-3). None of these genes have introns, and gene B-3 has an in-frame stop codon representing a pseudogene. Four genes, A-1, A-3, B-1, and B-2, are expressed in Samia brain. Genomic Southern hybridization suggests that the Samia genome contains many other SBRP genes.

Insect tissue culture systems: models for study of hormonal control of development

The regulation of growth and development of insects is under endocrine control and involves both juvenile hormones and ecdysteroids. Neuropeptides are master regulators which control the secretion of these hormones. Most experiments in insect endocrinology have been conducted in vivo, but tissue culture methodology is playing an increasing role due to the great interest in simpler model systems for the study of complex processes that occur in vivo. The availability of appropriate media has allowed the culture of a variety of insect organs and cell lines of defined origin which have kept certain properties of the parent tissues. Tissue culture approaches have been useful for studying hormonal control of morphogenetic processes. Cell lines are particularly suited to the study of hormonally regulated mechanisms of macromolecular biosynthesis and gene expression. Thus, the value of in vitro analysis in studies of regulation of hormone production is now recognized. Results obtained from tissue culture allow more precise definition of the hormonal requirements of insect cells and tissues for growth and differentiation and might make possible the discovery of new growth regulators.

Rapid isolation of a neurohormone from mosquito heads by high-performance liquid chromatography

Methods were developed for the isolation of the egg development neurosecretory hormone, EDNH, from heads of the mosquito Aedes aegypti. This hormone stimulates ecdysone production by ovaries. Methods used for the successful isolation of insulin-like peptides from vertebrate tissues were modified to develop a four-step procedure involving extraction in acidified ethanol, precipitation by neutralization, followed by sequential separation on size-exclusion, ion-exchange and reversed-phase high-performance liquid chromatography columns.

cDNAs from neurosecretory cells of brains of Locusta migratoria (Insecta, Orthoptera) encoding a novel member of the superfamily of insulins

From neurohaemal lobes of corpora cardiaca of Locusta migratoria a 5-kDa peptide has been isolated and its sequence established [see the accompanying paper, by Hietter et al. (1990) Eur. J. Biochem. 187, 241-247]. We have designed oligonucleotide probes from the peptide sequence of this molecule and screened a library prepared from mRNA of the neurosecretory cell region of the brain of this insect. Several positive cDNAs were isolated, the combined nucleotide sequences of which predict a large precursor of 145 residues (15770 Da) containing the newly isolated 5-kDa peptide. The peptide is flanked by regions homologous to the A and B chains of the superfamily of insulins. The overall organization of the precursor is as follows: signal peptide/domain homologous to the B chain of insulins/C (connecting)-peptide (corresponding to the newly isolated 5-kDa peptide)/domain homologous to the A chain of insulins. The numbers and relative positions of the cysteines of the Locusta peptide are equivalent to those of the other members of the insulin superfamily and most of the hydrophobic core residues are conserved.

Synthesis of bombyxin-IV, an insulin-like heterodimeric peptide from the silkworm, Bombyx mori

Bombyxin-IV, a molecular species of bombyxin, which is a member of insulin-like heterodimeric peptides of the silkworm Bombyx mori with prothoracicotropic hormone activity, was synthesized. The A- and B-chains of bombyxin-IV containing four and two Cys residues, respectively, were first synthesized separately by solid phase chemistry using Boc protocol. Then they were coupled by stepwise removal of two different protecting groups at the cysteinyl thiols for semiselective formation of disulfide bridges to give bombyxin-IV in 8% yield. The synthetic bombyxin-IV was shown to have chromatographic and biological properties identical with those of natural bombyxin-IV.