The transepithelial electrical potential decay across the isolated midguts of two larvae of lepidoptera (Bombyx mori and Philos amia cynthia)
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Progress made toward the elucidation of molecular features of the prothoracicotropic hormone (PTTH) of the silkmoth Bombyx mori is reviewed. PTTH stimulates the prothoracic glands to synthesize and release ecdysone, and is therefore a key hormone for the regulation of insect moulting and metamorphosis. Bombyx PTTH is a 30 kDa homodimeric glycoprotein, whose carbohydrate moiety is not essential for the biological function. The Bombyx genome contains a single copy of the PTTH gene. PTTH is produced by four dorsolateral neurosecretory cells of brain. Another Bombyx brain peptide exerting prothoracicotropic activity to a heterologous moth Samia cynthia ricini but no activity to Bombyx has been identified and termed bombyxin. Bombyxin is a 5 kDa heterodimeric peptide that shows a high similarity to insulin in the amino acid sequence. The bombyxin gene structure also shows a high similarity with the insulin gene structure. The Bombyx genome contains more than 30 copies of the bombyxin gene. Bombyxin is synthesized by eight dorsomedial neurosecretory cells of brain.
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ABSTRACT In silkworm, Bombyx mori Linnaeus (Lepidoptera: Bombycidae), blastokinesis results in embryo reversal from ventrally to dorsally convex flexion. In this study, we showed that the extramacrochaetae ( emc ) gene is required for blastokinesis in silkworm. Depletion of Bmemc expression via RNA interference led to severe phenotypic defects in blastokinesis. The defective embryos failed to invert their body sides during blastokinesis. This caused the posterior half of the abdomen to abnormally fold back toward the dorsal side, forming a U‐shaped morphology. Dorsal closure was also disrupted. Our results suggest that Bmemc is involved in blastokinesis of silkworm embryos. J. Exp. Zool. (Mol. Dev. Evol.) 324B: 405–409, 2015 . © 2015 Wiley Periodicals, Inc.
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Communication via specific chemical signals is vitally important for the reproductive behaviour of many species. The first identified sex-attractant pheromone was bombykol from the silkmoth Bombyx mori. This female-released signalling compound is perceived by the male moth with extreme sensitivity and specificity. Antennal sensory cells supposedly respond to individual bombykol molecules and can efficiently distinguish bombykol from highly related structural analogues like bombykal, a second female-released pheromone component. In the four decades since the discovery of bombykol, the Bombyx mori system has continued to serve as an invaluable model system for unraveling the intricacies of chemical communication. The molecular basis for this extraordinary specific recognition of an extraneous compound is still elusive but probably based on specific receptors of the pheromone-responsive cells. In this study, molecular and bioinformatic approaches were employed to search for candidate pheromone receptors of Bombyx mori. A few receptor types were identified that are related to Heliothis candidate pheromone receptors. They were found to be almost exclusively expressed in male antennae, and double in situ hybridization experiments disclosed a characteristic topographic expression pattern that was reminiscent of pheromone-responsive cells. Furthermore, the receptor-expressing cells were closely associated with cells expressing the pheromone-binding protein. Together, the data support the view that the identified receptor types of Bombyx mori are candidate receptors for pheromone components.
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Prothoracicotropic hormone (Bombyx PTTH) of the silkworm, Bombyx mori, was extracted from adult heads. Bombyx PTTH is suggested to be a glycopeptide and consists of two essentially identical subunits. Amino acid sequencing and cDNA analysis revealed the whole amino acid sequence of the subunit, composed of 104-109 residues. Bombyx PTTH stimulated adult development in brainless Bombyx pupae at a dose of ca. 0.1 ng and also enhanced the release of ecdysone in vitro at a concentration of 10-11 M. Immunohistochemistry and in situ hybridization showed that Bombyx PTTH was transcribed and translated in two pairs of dorso-lateral neurosecretory cells in the brain.
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In insects, the activity of phenoloxidase increases near the site of injury where it not only helps in wound healing but also prevents infection. The present study discusses the regulation of phenoloxidase by age dependent mechanical injury in the silkworm. The experiment was conducted on 4th and 5th instar silkworms with single and multiple wounding. A drastic increase in the enzyme activity was observed in 4th instar caterpillars upon a single wounding. Conversely, less enzyme activity was observed in 5th instar caterpillars upon single wounding but this increased with multiple wounding. This reveals the age dependent control over phenoloxidase activity in silkworm that may be essential in the later instars to prevent any autoimmune effect caused by the enzyme. Controlling enzyme activity may be a significant evolutionary strategy adapted by the caterpillar to regulate the energy investment during 5th instar. The results of the present study confirm the probability of the presence of a novel mechanism which regulates the activity of phenoloxidase in caterpillars at different instars.
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Silk proteins were isolated from the cocoons of the nonmulberry silkworm, Philosamia ricini. Three polypeptides of 97, 66, and 45 kDa were identified. The 66-kDa molecule represented sericin, whereas the 97-kDa and the 45-kDa polypeptides linked together through a disulfide bond constituted the fibroin protein. Antibodies raised against the 97-kDa P. ricini fibroin heavy chain reacted specifically with this molecule and did not recognize fibroin heavy chain from another nonmulberry silkworm, Antheraea assama or from the mulberry silkworm, Bombyx mori, suggesting the presence of P. ricini species-specific determinants in this heavy chain. Antibodies generated against fibroin light chain of P. ricini also showed similar reactivity pattern. Immunoblot analysis with proteins isolated from the silk glands of P. ricini at different stages of larval development showed that the expression of fibroin heavy chain was developmentally and spatially regulated. The protein was most abundant in the 5th instar larva, and could be detected in the middle and the posterior but not the anterior silk glands. The amino acid composition of the 97-kDa fibroin protein showed abundance of glutamic acid and did not contain (Gly-Ala)n motifs, a characteristic feature of B. mori fibroin heavy chain. Our study reveals significant differences between the nonmulberry silkworm P. ricini and the mulberry silkworm B. mori in the biochemical composition and immunochemical characteristics of fibroin heavy chain. These differences might be responsible for the differences seen in the quality of silk produced by these two silkworms.
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GlcNAcase is a glycosyl hydrolase located in the lysosomes of numerous organisms. Levels of the protein, β-N-acetylglucosaminidase 2 (GlcNAcase2), which is a member of the GlcNAcase family, are different in two strains of the silkworm Bombyx mori that have different resistance to Bombyx mori nucleopolyhedroviruses (BmNPVs). We identified six single-nucleotide differences in the GlcNAcase2 coding sequence between the 306 and NB strains. Five are silent changes, but one is a nonsynonymous mutation. Reverse transcription-polymerase chain reaction analysis showed that GlcNAcase2 mRNA levels in the NB strain were nearly 2.57 times higher compared with those in the 306 strain. In addition, GlcNAcase2 enzyme activity was much higher in the NB strain compared with that in the 306 strain. Together, these results indicate that GlcNAcase2 may be involved in variable BmNPV resistance in B. mori .
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Adult eclosion of the silkworm, Bombyx mori, occurs during a specific period of the day under the control of eclosion hormone (EH). Bombyx EH was extracted from the pupal and adult brains (Fugo, et al., 1982), and also the embryos of B. mori (Chen, et al., 1986). In 1985, Bombyx EH was first isolated from the pharate adult heads of B. mori (Nagasawa, et al., 1985). Recently the entire amino acid sequence of Bombyx EH was determined as shown in Fig. 1 through the combination of sequencing the isolated Bombyx EH (Kono, et al., 1987) and cloning the Bombyx EH gene. A monoclonal antibody against the synthetic peptide corresponding to the carboxyl-terminal 13 amino acid residues of Bombyx EH was prepared (Kono, et al., in press).
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