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PubMed1999

Titres of biogenic amines and ecdysteroids: effect of octopamine on the production of ecdysteroids in the silkworm Bombyx mori.

At day two, a sharp peak of octopamine (OA) was observed in last instar female Bombyx mori larvae. This peak also appeared in male larvae a day later than in females at day three. An OA peak was also observed before the 3rd ecdysis. However, no OA peaks were observed in 4th instar larvae. At day eight and nine of the 5th instar, another OA peak was observed for male and female, respectively. A peak of tyramine (TA) was found at day one followed by a peak of OA at day two in 3rd instar larvae. At day two, a day before OA peak, a peak of TA was observed for male insects and before the 2nd peak of OA, TA titre was also high in 5th instar larvae. Immediately after 3rd ecdysis, a high titre of DL-beta-(3,4-dihydroxyphenyl)alanine (DOPA) was observed, followed by a peak of dopamine (DA) at day five. A peak of DOPA was found at day one followed by a peak of DA at day two in 3rd instar larvae. Similarly, a small peak of DOPA was observed at day two, followed by an increase of DA at days eight and nine after the 4th ecdysis. Ecdysteroid peaks were observed just before the 3rd and 4th ecdysis and an ecdysteroid titre increased after the start of spinning. The effects of OA and JH on production of ecdysteroids by prothoracic glands (PGs) were examined in order to identify neuromediators responsible for triggering pupation in B. mori larvae. Exogeneous OA (10-100 mM) reduced and 10 &mgr;M OA stimulated the production of ecdysteroids in the presence and absence of brain extracts by PGs in the final instar (day five) of B. mori in vitro. Meanwhile, exogeneous JHI (10 &mgr;g/ml) stimulated and at 5 &mgr;g/ml it reduced production of ecdysteroids in the presence of brain extracts. Gramine, an OA antagonist, delayed pupation when applied in the diet. Thus, OA may produce some biological effects on the programming of larval-pupal development.

Journal Article↗
PubMed1999

Presence of eupyrene spermatozoa in vestibulum accelerates oviposition in the silkworm moth, Bombyx mori.

In the silkmoth, Bombyx mori, mating accelerates egg laying. Sterilized males did not induce females to oviposit, whereas artificial insemination was enough to accelerate oviposition. These findings showed that mechanical stimulation of the outer reproductive organs and the bursa copulatrix (BC) had no effect on oviposition. Factors included in seminal fluids also did not stimulate oviposition because neither implantation of female internal reproductive organs nor injection of the spermatophore extract into virgin females activated oviposition. Preventing sperm precedence by experimental removal of the BC or spermatheca inhibited activation of egg laying. More precise surgeries on the spermatheca showed that the main factor for eliciting oviposition was the presence of matured and fertile eupyrene spermatozoa in the vestibulum. Sperm were not effective unless they reached the vestibulum. Nerve transection and electrophysiological studies revealed that nerve 4 of the terminal abdominal ganglion was the pathway by which the mating signal was transmitted toward the higher central nervous system.

Journal Article↗
PubMed1982

Regulatory effects of temperature and hemolymph on inhibition and enhancement of attachment and filopodia function of phagocytic granular cells of the silkworm, Bombyx mori.

The effect of temperature on the adhesiveness and filopodia elongation of granular cells was examined in the presence or absence of hemolymph. The incubation in hemolymph remarkably increased the number of adherent cells almost irrespective of temperatures. Marked inhibition of attachment was seen in incubation media without hemolymph or with 20% hemolymph but at much lower temperatures. Filopodia elongation was markedly inhibited at a low temperature even when the cells were incubated in hemolymph alone. However, the number of filopodia-elongated cells was increased by raising the temperature even without hemolymph. These results show that hemolymph of B. mori is suggested to contain at least two kinds of humoral factors which affect the initial phases of cellular reactions to foreign materials. One is to promote attachment and the other to activate filopodia function. Moreover, it is shown that attachment is a temperature-independent process in the presence of hemolymph unlike filopodia elongation. However, since both attachment and filopodia elongation were increased by raising the temperature, temperature is considered to be another important cofactor in enhancement of foreignness-recognition and binding ability.

Animals↗
PubMed1998

Characterization of aminopeptidase N from the brush border membrane of the larvae midgut of silkworm, Bombyx mori as a zinc enzyme.

Three GPI-anchored proteins, aminopeptidase N, alkaline phosphatase and alkaline phosphodiesterase I were released from the midgut brush border membrane of Bombyx mori by phosphatidylinositol-specific phopholipase C and the aminopeptidase N was purified to a homogeneous state. N-terminus and 6 internal sequences, one of which possessed part of zinc-binding motif, showed homology with those from other species. The zinc content in purified aminopeptidase N was estimated as approximately 0.72 mol/mol of the protein and 1,10-phenanthroline completely inhibited the enzyme activity, suggesting zinc requirement for the activity. The aminopeptidase N activity was inhibited not only by probestin and actinonin, but also strongly depressed by amastatin, while leuhistin and bestatin were less inhibitory. These suggest that the active site of aminopeptidase N might be structurally different from those of mammals. Calcium and magnesium ions stimulated the aminopeptidase N activity, but copper ion was rather inhibitory. Zinc ion showed bi-modal effect on the activity, i.e., stimulatory at low concentration, but inhibitory at higher than 100 microM. This inhibition was completely restored by EDTA. These results suggest that the aminopeptidase N possesses two zinc ion-binding sites with high and low affinity as essential and inhibitory one, as well as some regulatory metal-binding sites.

Amino Acid Sequence↗
PubMed2002

Solution structure of paralytic peptide of silkworm, Bombyx mori.

Paralytic peptide of Bombyx mori (BmPP) is one of the multifunctional ENF-peptides; the name of "ENF" is the consensus N-terminal amino acid sequence of the family peptides. We revealed that BmPP significantly possesses growth-blocking activity and plasmatocyte-spreading activity and that its activity profiles are different from those of another ENF-family peptide, namely, the growth-blocking peptide of Pseudaletia separata (PsGBP). We also determined the NMR structures of BmPP and PsGBP under the same conditions, which revealed the structural differences of the first and second beta-turn regions between the two peptides. On the basis of our results, it can be considered that the tertiary structural difference in these peptides may cause their different profiles of growth-blocking activity.

Amino Acid Sequence↗
PubMed1999

cDNA cloning and gene expression of cecropin D, an antibacterial protein in the silkworm, Bombyx mori.

We have isolated a cDNA clone encoding a cecropin D precursor from the fat body of Bombyx mori larvae immunized with bacteria by means of differential display. The cDNA contains 298 bp with a coding region of 183 bp for 61 amino acids plus a termination codon (TAG), a 5'-untranslated region of 36 bp, and a 3'-untranslated region of 79 bp including the poly(A) tail. There is a polyadenylation signal sequence of AATAAA at position 266, 43 nucleotides downstream from the termination codon TAG. The homology of the deduced amino acids is greater to the cecropin D precursor from Hyalophora cecropia (67% identity) than to the precursors of cecropins A and B from B. mori (49% to both). Northern blotting analyses reveal that the gene expression of cecropin D is detectable by 4 h after the bacterial injection and reaches the maximal level at 24 h. That high level is maintained up to 48 h post-immunization. Additionally, the gene is expressed mainly in the fat body and slightly in hemocytes, but it is undetectable in other tissues such as the midgut, the Malpighian tubule and silk gland.

Amino Acid Sequence↗
PubMed1999

Involvement of calcineurin in the signal transduction of PBAN in the silkworm, Bombyx mori (Lepidoptera).

In several moth species sex pheromone production in the pheromone gland is regulated by a neurohormone, pheromone biosynthesis activating neuropeptide (PBAN). In Bombyx mori it is suggested that PBAN, after binding to the cell-surface receptor, primarily activates a plasma membrane receptor-activated Ca2+ channel to increase cytosolic levels of Ca2+, and Ca2+/calmodulin complex directly or indirectly activates a phosphoprotein phosphatase, which in turn elicits activation of acyl CoA reductase (the key enzyme under PBAN control) through dephosphorylation, resulting in pheromone (bombykol) production. The effect of cyclosporin A (CsA) and FK 506, specific inhibitors of calcineurin (phosphoprotein phosphatase 2B) was studied on the sex pheromone production, in B. mori. The in vitro experiments showed that both chemicals exerted a dose-dependent inhibitory action when they were co-incubated with TKYFSPRL amide (Hez-PBAN fragment peptide). Practically, no difference was detected between the two chemicals in the tested doses (0.025-1250 microM). When effects of CsA or FK 506 were studied on cell-free production of bombykol by using microsomal fraction no inhibition was detected. Since microsomal fraction contains the acyl CoA synthetase, the rate-limiting acyl CoA reductase and the precursor, bombykol is produced if supplied with CoA, ATP and NADPH. Thus, the inhibitory action of CsA and FK506 under in vitro conditions should occur before the step of acyl group reduction and the effect is likely to be attributable to the inhibition of calcineurin in the signal transduction cascade mechanism of PBAN, in B. mori. The existence of calcineurin in the pheromone gland by using Western blot analysis is also demonstrated.

Animals↗