Neuroendocrine control of diapause hormone secretion in the silkworm,Bombyx mori

To clarify the control mechanism of diapause hormone (DH) secretion in the silkworm Bombyx mori a series of anatomical and pharmacological experiments were carried out. The arrangement of 'diapause' and 'non-diapause' eggs in the ovarioles of the moths was determined by the coloration method to estimate the accumulation of 3-hydroxykynurenine in the eggs. The females destined to lay non-diapause eggs (non-diapause producers) had diapause eggs in their ovaries if their subesophageal ganglions (Sg) had been surgically removed at 2days after larval-pupal ecdysis or later. In contrast when the surgical extirpation extended to the brain and the corpora cardiaca (CC)-corpora allata (CA) complex in addition to the Sg, the non-diapause producers had no diapause eggs. When the Sg was removed from the females destined to lay diapause eggs (diapause-producers), diapause eggs appeared in response to the treatment at 2days after larval-pupal ecdysis, but the appearance of diapause eggs was delayed by 2days when the brain-CC-CA complex was included among the organs removed. These observations suggested that DH is produced in Sg and transferred to the CC-CA complex, and that the secretion of DH from the complex is suppressed in non-diapause producers. The pattern of diapause and non-diapause eggs induced by the transection of the subesophageal connective in diapause and non-diapause producers suggested a regenerative and secretory capacity of the neurosecretory cells after the operation. The appearance of diapause eggs in non-diapause producers with transected protocerebrum of the brain confirmed that there was an inhibitory center in the protocerebrum. Changes in parts of the ovarioles containing diapause and non-diapause eggs with time of injection of gamma-aminobutyric acid (GABA) and picrotoxin suggested that a GABAergic inhibitory mechanism in DH secretion may be active in non-diapause producers but inactive in diapause producers throughout the pupal stage.     

Effect of diapause hormone on cyclic nucleotide metabolism in developing ovaries of the silkworm, Bombyx mori

1. The content of cyclic AMP and cyclic GMP in ovaries of the silkworm, Bombyx mori, changed differently depending on development. 2. The extirpation of suboesophageal ganglion caused cyclic AMP to decrease and cyclic GMP to increase at different developmental stages. 3. The reversed changes in the cyclic nucleotides were brought about by implantation of the ganglion or by injection of the diapause hormone preparation. 4. No change in both cyclic nucleotides was induced in ovaries during the first 24 hr after an injection of the hormone, but the clear effects appeared after a lag phase of a few days.     

Studies on embryonic diapause in thepnd mutant of the silkworm,Bombyx mori

Summary Two-dimensional gel electrophoresis has been used to analyse patterns of proteins synthesized in the eggs from theBombyx mutantpnd, whose homozygous embryo never enters diapause owing to a genetic defect. At the middle to late stage of gastrulation the diapause type of the heterozygous embryo, derived from a homozygouspnd female mated to a wild-type male, synthesizes eight proteins which are not detected in the homozygouspnd embryo. To examine the relationship between embryonic diapause and the appearance of the heterozygote-specific proteins, the pattern of proteins synthesized in the heterozygotes of the diapause type was compared with that in heterozygotes which were artificially altered so that they would continue development. Only one of the eight heterozygote-specific proteins was constitutively synthesized according to the embryonic genome, irrespective of their developmental state, whereas appearance of the remaining seven proteins was exclusively dependent on their developmental nature. This finding strongly suggests that the unique protein might result from the expression of thepnd ⁺ gene, and the other proteins might be synthesized along with diapause initiation in the heterozygotes. The possible role of the putativepnd ⁺ gene-specific protein at the onset of embryonic diapause is discussed in relation to the action of the diapause factor, which predetermines embryonic diapause by affecting the developing oocytes.     

Studies on the embryonic diapause of thepnd mutant of the silkworm,Bombyx mori

Summary The changing pattern in free amino acids following the embryonic development in the non-diapause and diapause eggs of thepnd mutant of theBombyx silkworm was studied. In the diapause eggs, heterozygous for thepnd gene, the levels of most of the amino acids increased concomitantly with the substantial decrease in oxygen consumption. Among the amino acids, alanine was the only amino acid that showed a large accumulation. The accumulation could be induced experimentally in the non-diapause eggs, homozygous for thepnd gene, by reducing the oxygen supply. In contrast, it was prevented in the diapause eggs by increasing the oxygen supply. From these results, it is suggested that the alanine accumulation is the consequence of anaerobic metabolism in the eggs during diapause. The possible significance of the alanine accumulation is discussed in relation to the anaerobic carbohydrate metabolism associated with the embryonic diapause in thepnd mutant.     

Isolation of three main sericin components from the cocoon of the silkworm,Bombyx mori

To characterize the sericin components of the cocoon of silkworm Bombyx mori, fresh cocoon shells were dissolved in saturated aqueous lithium thiocyanate containing 2-mercaptoethanol, and fractionated by ethanol precipitation. Cocoon sericin was found to mainly consist of three polypeptides having molecular masses of the 400, 250, and 150 kDa estimated by SDS-PAGE, which corresponds to the sericin present in the middle, anterior, and posterior part of the middle silk gland. The amino acid compositions of the 400 and 150 kDa components were similar to each other, but that of the 250 kDa component was different. This suggests differences in the coding gene and properties of the 250 kDa sericin from the other two.     

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.     

Isolation and amino terminal sequence of melanization and reddish coloration hormone (MRCH) from the silkworm,Bombyx mori

Cuticular melanization associated with the gregarious phase of the common armyworm larvae, Leucania separata, is caused by a neurohormone, melanization and reddish coloration hormone (MRCH). Two molecular species of MRCH were isolated from 211,000 heads of adult Bombyx mori with conventional column chromatography and reversed-phase high performance liquid chromatography. As little as 6 ng of purified MRCH elicited marked melanization in the cuticle of an L. separata larva. Automated Edman degradation confirmed 16 residues of N-terminal amino acid sequences of the purified MRCHs; these showed homology with each other.     

Proteome profile of spinneret from the silkworm,Bombyx mori

The silkworm spinneret is an important tissue for silk fibrillogenesis and spinning. All biochemical processes during silk fibrillogenesis are correlated with silk properties. Understanding the role of spinneret in silk fibrillogenesis may help to reveal the mechanism of silk fibrillogenesis as well as improve silk quality for commercial purposes. Thus, we profiled the proteome of silkworm spinneret. A total of 1572 proteins and 232 differential abundance proteins were identified. Silk fibrillogenesis‐related proteins, such as cuticle proteins, ion‐transporting proteins, muscular proteins, and energy metabolic proteins, were abundant in spinneret. Metabolic pathway and GO enrichment analyses revealed that the identified proteins were involved in energy metabolism, chitin binding, and cuticle construction. Active energy metabolism may provide abundant energy for the muscle contraction as well as ion and water exchange. The chitin binding and cuticle construction process may provide sufficient shear forces for silk formation. Our data suggest that silkworm spinneret provides a suitable physiological and biochemical environment for silk fibrillogenesis. These proteins are potential targets for improving silk quality in the silk industry. Data are available via ProteomeXchange with identifier PXD004455.     

Isolation of a cDNA encoding a CHH-family peptide from the silkworm Bombyx mori

The crustacean hyperglycemic hormone (CHH) peptide family includes four types of neuropeptide in decapod and isopod crustaceans, and the ion-transport peptide in orthopteran insects. To identify a new member of this family in Insecta, a PCR-based search for cDNAs encoding CHH-family peptides was carried out in the silkworm Bombyx mori. A cDNA, named BmCHHL (Bombyx mori CHH-like protein), with an open reading frame of 110 amino acids was isolated. Sequence analyses suggested that the conceptual protein was a precursor of a peptide of 72 amino acids which was amidated at the carboxy terminus. The BmCHHL sequence exhibited significant similarities to members of the CHH family including the orthopteran ion-transport peptide. BmCHHL expression was detected in five or six cells (per hemisphere) in the frontal area of the brain in day 4 fifth instar larvae.     

Isolation and properties of carboxylesterase from hemolymph of the silkworm Bombyx mori L

An original procedure for isolation and purification of carboxylesterase from the hemolymph of stage V larvae of one of Bombyx mori strains including precipitation with 10% polyethyleneglycol, ion-exchange chromatography on Sephadex G-200 and chromatography on DEAE-Sephadex A-50, has been developed. The specific activity of the enzyme after purification makes up to 1250 units per mg of protein with a 59% yield. Some physicochemical properties of the enzyme (Mr = 69 000, pI congruent to 4.9, temperature optimum = 40 degrees, pH optimum = 7.2 Km for alpha-naphthyl- and beta-naphthylacetate = 0.11 X 10(-3) and 0.52 X 10(-3) M, respectively) have been determined. Using immunodiffusion in agar gel, the antigenic identity of the enzymes isolated from the hemolymph of two silkworm species has been established.     

家蚕滞育卵与非滞育卵中几种关键酶活性的比较

家蚕Bombyx mori是卵滞育的昆虫, 在滞育期间无形态变化, 也不存在器官发育和组织分化, 然而其生理代谢过程仍在进行。为进一步研究家蚕滞育的机制, 本研究测定了家蚕滞育卵、 即时浸酸处理的滞育卵及非滞育卵在胚胎发育过程中的超氧化物歧化酶(superoxide dismutase, SOD, EC 1.15.1.1)、 过氧化氢酶(catalase, CAT, EC 1.11.1.6)、 丙酮酸激酶(pyruvate kinase, PK, EC 2.7.1.40)、 乙酰胆碱酯酶(acetylcholine esterase, AchE, EC 3.1.1.7)和乳酸脱氢酶(lactate dehydrogenase, LDH, EC 1.1.1.28) 的活性变化。结果表明： 处理后1-7 d, 即时浸酸处理的滞育卵, SOD活性由56 517.00 U/g提高到81 986.94 U/g, CAT活性由14.98 U/g提高到106.90 U/g, PK活性由25.19 U/g提高到181.70 U/g, AChE活性由17.88 U/g提高到287.86 U/g, 而LDH活性由169.96 U/g下降到122.82 U/g。 而在非滞育卵中, SOD活性由86 417.99 U/g下降到66 024.19 U/g, LDH活性由169.07 U/g下降到135.02 U/g; CAT活性由1.47 U/g提高到44.37 U/g, PK活性由20.56 U/g提高到92.09 U/g, AChE活性由21.40 U/g提高到99.17 U/g。在滞育卵中, SOD和AChE活性较稳定; CAT活性随发育上升, 而LDH活性随发育而下降; PK活性在胚胎发育的前 4 d呈上升趋势, 随后基本保持稳定。通过了解家蚕滞育卵、 非滞育卵与即时浸酸卵的相关酶活性在胚胎发育过程中存在的变化, 有助于进一步揭示家蚕滞育的机理。     

Isolation and nucleotide sequence of cecropin B cDNA clones from the silkworm, Bombyx mori.

Two cDNA clones encoding cecropin B, an antibacterial protein, were isolated from a fat body cDNA library of the silkworm, Bombyx mori. Amino acid sequences of these clones, deduced from nucleotide sequences, were identical, including signal peptide regions. However, the nucleotide sequences were different at 30 positions. Deduced amino acid sequences of Bombyx mori cecropin B showed higher homology with cecropins from Lepidoptera than with those from Diptera.     

Storage proteins in the silkworm,Bombyx mori

In the silkworm, Bombyx mori, two storage proteins named SP-1 and SP-2 were shown to decline in concentration in the haemolymph and increase in the fat body during the larval-pupal transformation, when protein granules are formed in the fat body at the same time as the degeneration of mitochondria and endoplasmic reticulum. At the larval-pupal ecdysis, in females the two proteins account for 60% of total fat body protein (80% of the soluble protein), while males have very little SP-1 and SP-2 comprises only 20% of the total fat body protein. The concentration of protein granules in the fat body cytoplasm is much greater in females than in males, and the granules in females have partially crystalline inner zones. This is different from males where granules with non-crystalline structure are most numerous.The properties of these proteins purified from pupal fat body are similar to those of Cecropia storage proteins and calliphorin, all of which have molecular weights of around 500,000 and are composed of subunits of mol. wt about 85,000. SP-1 differs from SP-2 by having an exceptionally high content of methionine, but much less glutamate, phenylalanine and tyrosine. SP-1 resembles another female-specific protein, vitellogenin and SP-2 resembles calliphorin in amino acid composition.From these results, it is concluded that SP-1 and SP-2 have storage roles and are deposited in protein granules.