The biological role of core 1β1-3galactosyltransferase (T-synthase) in mucin-type O-glycosylation in Silkworm, Bombyx mori

O-glycosylation of secreted and membrane-bound proteins is an important post-translational modification that affects recognition of cell surface receptors, protein folding, and stability. However, despite the importance of O-linked glycans, their biological functions have not yet been fully elucidated and the synthetic pathway of O-glycosylation has not been investigated in detail, especially in the silkworm. In this study, we aimed to investigate O-glycosylation in silkworms by analyzing the overall structural profiles of mucin-type O-glycans using LC-MS. We found GalNAc or GlcNAc monosaccharide and core 1 disaccharide (Galβ1-3-GalNAcα1-Ser/Thr) were major components of the O-glycan attached to secreted proteins produced in silkworms. Furthermore, we characterized the 1 b1,3-galactosyltransferase (T-synthase) required for synthesis of the core 1 structure, common to many animals. Five transcriptional variants and four protein isoforms were identified in silkworms, and the biological functions of these isoforms were investigated. We found that BmT-synthase isoforms 1 and 2 were localized in the Golgi apparatus in cultured BmN4 cells and functioned both in cultured cells and silkworms. Additionally, a specific functional domain of T-synthase, called the stem domain, was found to be essential for activity and is presumed to be needed for dimer formation and galactosyltransferase activity. Altogether, our results elucidated the O-glycan profile and function of T-synthase in the silkworm. Our findings allow the practical comprehension of O-glycosylation required for employing silkworms as a productive expression system.

Silkworm FoxL21 plays important roles as a regulator of ovarian development in both oogenesis and ovariole development

The ovary is an important organ in reproduction. In insects, especially lepidopteran insects, the oocytes and reproductive organs develop rapidly during the pupal stage. Despite their drastic morphological changes, the molecular mechanisms of ovary development are not fully understood. In this study, it is found that forkhead box transcription factor L2, member 1 (FoxL21), which is known to be involved in ovarian differentiation and maintenance in vertebrates, is required for the development of the ovary in the silkworm, Bombyx mori. FoxL21 was expressed in the ovary and ovariole during the larval and pupal stage, respectively. In silkworms in which FoxL21 was knocked out by genome editing, multiple ovarian dysfunctions, such as, abnormal egg formation, thinning of the ovariole sheaths, and defective connection of the oviductus geminus with the ovariole were observed. Finally, ovarian transplantation experiments using the knockout silkworms revealed that FoxL21 functions in the ovariole, but not in the oviductus geminus.

Non-molting dwarf (nm-d) as a mutant of Bombyx mori with a defect in purine synthesis

There are several known non-molting mutations of the silkworm, Bombyx mori, including non-molting dwarf (nm-d). Larvae with this mutation hatch normally and start eating leaves, but die before the completion of the first ecdysis. Genetic analysis of the nm-d mutation would contribute to the isolation of essential genes for the larval development of lepidopteran insects. To identify the causative gene of the nm-d locus, we conducted RNA-seq based rough mapping. Using two sets of RNA-seq data, one from a pooled sample of normal larvae, and one from a pooled sample of nm-d larvae, the nm-d locus was narrowed to a 500 kb region. Among the genes located in this region, a nm-d-specific exon loss was identified in the Bombyx homolog of the ATIC (5-aminoimidazole-4-carboxamide ribonucleotide transformylase/Inosine 5'-monophosphate cyclohydrolase) (BmATIC) gene, which catalyzes the final two steps of the de novo purine biosynthetic pathway in mammals. PCR and subsequent sequencing analysis revealed that a region containing exon 9 of the BmATIC gene is deleted in the nm-d larvae. A knockout allele of the BmATIC gene (BmATIC^KO), that was generated using the CRISPR/Cas9 system, revealed that first instar knockout larvae died while exhibiting the dark brown larval body that is a typical feature of mutants that lack uric acid in the integument. Lethal larvae resulted from crosses between +/BmATIC^KO moths. The uric acid content in the whole-body of the first instar was drastically reduced in the nm-d larvae compared to normal larvae. These results indicated that the BmATIC gene is responsible for the nm-d phenotype, and that nm-d larvae have a defect in purine biosynthesis, including uric acid. We also discuss the possibility that the BmATIC mRNA is maternally transmitted to eggs. Our results indicated that RNA-seq based mapping using pooled samples is a practical method for the identification of the causative genes of lethal mutations.

A defect in purine nucleotide metabolism in the silkworm, Bombyx mori, causes a translucent larval integument and male infertility

p-oily (op) is a novel mutant of Bombyx mori exhibiting translucent larval integument and male infertility. Elucidation of the causative gene of the op mutant will help understand the genetic mechanism underlying larval integument coloration and male fertility. Using polymorphisms between B. mori and B. mandarina, the op locus was narrowed down to a 375-kb region. Using RNA-seq analysis, we found that op mutants have a frameshift mutation in the KWMTBOMO13770 gene located in the 375-kb region. A database search indicated that this gene is the human cytosolic 5'-nucleotidase II gene (cN-II) homolog in Bombyx, which mediates the conversion of inosine monophosphate (IMP) to inosine, a precursor of uric acid. CRISPR/Cas9-mediated knockout mutants of the Bm-cN-II gene showed translucent integuments, and there appeared translucent larvae in the crosses between knockout moths and +/op moths. Moreover, the translucent phenotype of, and decreased uric acid content in the larval integument caused by the mutations in the Bm-cN-II gene were rescued by oral administration of inosine. These results indicated that the Bm-cN-II gene is responsible for the op phenotype and that the molecular function of the Bm-cN-II gene is the conversion of IMP to inosine. We also discuss the genetic relationship between the Bm-cN-II gene and male fertility.

Embryonic stage selection for cryopreservation of the silkworm Bombyx mori and the effects of cryopreservation on embryo tissues

Successful cryopreservation of the important silkworm bioresource, Bombyx mori, is essential. In this study, we aimed for successful cryopreservation using vitrification of silkworm embryos. Furthermore, the embryos were assessed for the most appropriate sampling stage. We found that vitrified embryos developed to the serosa ingestion stage when they were vitrified at embryonic stage 24-25. The most suitable stage for vitrification was around a 5-10 h period when the tracheal fibers were elongating in stage 25. None of the vitrified embryos developed into larvae, although some did develop to the pre-hatching stage. From histological analysis, we found that several small cracks formed on the cuticle covering the hypodermis in the vitrified embryos. Additionally, the midgut epithelium was detached from the midgut wall and mixed with the yolk in the midgut lumen. We speculate that the vitrified embryos died from a rapid loss of body water from the small cracks formed in the cuticle. We also suggest that the vitrified embryos may have resulted in dysfunction of the midgut.

Identification of a novel function of the silkworm integument in nitrogen metabolism: Uric acid is synthesized within the epidermal cells in B. mori

During nitrogen metabolism, animals convert toxic ammonia to less toxic forms. Uric acid (UA) is an end product of this process in terrestrial insects. In lepidopteran larvae, a large amount of UA is stored in the integument via a phenomenon known as storage excretion. Physiologically, integumental UA plays crucial roles as a barrier against sunlight and as a white pigment for larval pigmentation patterns. Conventionally, UA is thought to be synthesized in the fat body, the insect equivalent of the liver of vertebrates, and to be transported to the epidermis via the hemolymph. Here, we reconsidered the conventional theory by a mosaic analysis targeting genes governing UA synthesis, using CRISPR/Cas9 mutagenesis and a traditional genetic method in Bombyx mori. Notably, we observed mosaic larvae in which the integument comprised both UA-containing white and UA-lacking translucent areas, indicating that UA synthesis in the epidermis is indispensable to the accumulation of a large amount of highly insoluble UA in the epidermis. Our results thus provide a genetic basis for storage excretion wherein lepidopteran insects use nitrogenous waste to adapt to their environment.

Proteomic Analysis of Larval Integument in a Dominant Obese Translucent (Obs) Silkworm Mutant

The dominant obese translucent (Obs) mutant of the silkworm (Bombyx mori) results in a short and stout larval body, translucent phenotype, and abnormal pigmentation in the integument. The Obs mutant also displays deficiency in ecdysis and metamorphosis. In the present study, to gain an understanding of multiple Obs phenotypes, we investigated the phenotypes of Obs and performed a comparative analysis of the larval integument proteomes of Obs and normal silkworms. The phenotypic analysis revealed that the Obs larvae were indeed short and fat, and that chitin and uric acid content were lower but melanin content was higher in the Obs mutant. Proteomic analysis revealed that 244 proteins were significantly differentially expressed between Obs and normal silkworms, some of which were involved in uric acid metabolism and melanin pigmentation. Twenty-six proteins were annotated as cuticular proteins, including RR motif-rich cuticular proteins (CPR), glycine-rich cuticular protein (CPG), hypothetical cuticular protein (CPH), cuticular protein analogous to peritrophins (CPAPs), and the chitin_bind_3 motif proteins, and accounted for over 84% of the abundance of the total significantly differentially expressed proteins. Moreover, 22 of the 26 cuticular proteins were downregulated in the Obs mutant. Comparative proteomic analysis suggested that the multiple phenotypes of the Obs mutant might be related to changes in the expression of proteins that participate in cuticular formation, uric acid metabolism, and melanin pigmentation. These results could lay a basis for further identification of the gene responsible for the Obs mutant. The data have been deposited to ProteomeXchange with identifier PXD010998.

A reexamination on the deficiency of riboflavin accumulation in Malpighian tubules in larval translucent mutants of the silkworm, Bombyx mori

A variety of insects accumulate high contents of riboflavin (vitamin B₂) in their Malpighian tubules (MTs). Although this process is known to be genetically controlled, the mechanism is not known. In the 1940s and the 1950s, several studies showed that riboflavin contents were low in the MTs of some Bombyx mori (silkworm) mutants with translucent larval skin mutations (e.g., w-3, od, oa, and otm) and that genes responsible for these translucent mutations also affected riboflavin accumulation in the MTs. Since the 2000s, it has been shown that the w-3 gene encodes an ABC transporter, whereas genes responsible for od, oa, and otm mutations encode for the biogenesis of lysosome-related organelles. These findings suggest that some genes of ABC transporters and biogenesis of lysosome-related organelles may control the accumulation of riboflavin in MTs. Therefore, we reexamined the effects that translucent mutations have on the accumulation of riboflavin in MTs by using the translucent and wild-type segregants in mutant strains to measure the specific effect that each gene has on riboflavin accumulation (independent of genomic background). We used nine translucent mutations (w-3^oe, oa, od, otm, Obs, oy, or, oh, and obt) even though the genes responsible for some of these mutations (Obs, oy, or, oh, and obt) have not yet been isolated. Through observation of larval MTs and measurements of riboflavin content using high-performance liquid chromatography, we found that the oa, od, otm, and or mutations were responsible for low contents of riboflavin in MTs, whereas the Obs and oy mutations did not affect riboflavin accumulation. This indicates that the molecular mechanism for riboflavin accumulation is similar but somewhat different than the mechanism responsible for uric acid accumulation in epidermal cells. We found that the genes responsible for oa, od, and otm mutations were consistent with those already established for uric acid accumulation in larval epidermis. This suggests that these three genes control riboflavin accumulation in MTs through a mechanism similar to that of uric acid accumulation, although we do not yet know why the or mutation also controls riboflavin accumulation.

Translucent larval integument and flaccid paralysis caused by genome editing in a gene governing molybdenum cofactor biosynthesis in Bombyx mori

Translucency of the larval integument in Bombyx mori is caused by a lack of uric acid in the epidermis. Hime'nichi translucent (ohi) is a unique mutation causing intermediate translucency of the larval integument and male-specific flaccid paralysis. To determine the gene associated with the ohi mutation, the ohi locus was mapped to a 400-kb region containing 29 predicted genes. Among the genes in this region, we focused on Bombyx homolog of mammalian Gephyrin (BmGphn), which regulates molybdenum cofactor (MoCo) biosynthesis, because MoCo is indispensable for the activity of xanthine dehydrogenase (XDH), a key enzyme in uric acid biosynthesis. The translucent integument of ohi larvae turned opaque after injection of bovine xanthine oxidase, which is a mammalian equivalent to XDH, indicating that XDH activity is defective in ohi larvae. RT-PCR and sequencing analysis showed that (i) in ohi larvae, expression of the BmGphn gene was repressed in the fat body where uric acid is synthesized, and (ii) there was no amino acid substitution in the ohi mutant allele. Finally, we obtained BmGphn knockout alleles (hereafter denoted as BmGphn^Δ) by using CRISPR/Cas9. The resulting ohi/BmGphn^Δ larvae had translucent integuments, demonstrating that BmGphn is the gene responsible for the ohi phenotype. Our results show that repressed expression of BmGphn is a causative factor for the defective MoCo biosynthesis and XDH activity observed in ohi larvae. Interestingly, all male BmGphn^Δ homozygotes died before pupation and showed a flaccid paralysis phenotype. The genetic and physiological mechanisms underlying this flaccid paralysis phenotype are also discussed.

Discovery of a New Species of Telenomus (Hymenoptera: Scelionidae) Parasitic on Eggs of Bombyx mandarina and Bombyx mori (Lepidoptera: Bombycidae) in Japan and Taiwan

We reared a Telenomus species from eggs of Bombyx mandarina (Moore) (Lepidoptera: Bombycidae) and Bombyx mori (Linnaeus) (Lepidoptera: Bombycidae) in Japan, and from eggs of B. mandarina in Taiwan. Morphological examination revealed that this Telenomus species is new to science. In this article, we describe it as Telenomus moricolus Matsuo et Hirose, sp. nov. Because B. mandarina is considered to be an ancestor of B. mori, a domestic insect, it is reasonable to assume that B. mandarina is an original host of T. moricolus. This is the second discovery of an egg parasitoid attacking wild and domesticated silkworms, following the first discovery of T. theophilae, a Chinese species. The significance of the discovery of T. moricolus is discussed in relation to examining the effects of host-insect domestication on egg parasitism.

Characterization of Recombinant Thermococcus kodakaraensis (KOD) DNA Polymerases Produced Using Silkworm-Baculovirus Expression Vector System

The KOD DNA polymerase from Thermococcus kodakarensis (Tkod-Pol) has been preferred for PCR due to its rapid elongation rate, extreme thermostability and outstanding fidelity. Here in this study, we utilized silkworm-baculovirus expression vector system (silkworm-BEVS) to express the recombinant Tkod-Pol (rKOD) with N-terminal (rKOD-N) or C-terminal (rKOD-C) tandem fusion tags. By using BEVS, we produced functional rKODs with satisfactory yields, about 1.1 mg/larva for rKOD-N and 0.25 mg/larva for rKOD-C, respectively. Interestingly, we found that rKOD-C shows higher thermostability at 95 °C than that of rKOD-N, while that rKOD-N is significantly unstable after exposing to long period of heat-shock. We also assessed the polymerase activity as well as the fidelity of purified rKODs under various conditions. Compared with commercially available rKOD, which is expressed in E. coli expression system, rKOD-C exhibited almost the same PCR performance as the commercial rKOD did, while rKOD-N did lower performance. Taken together, our results suggested that silkworm-BEVS can be used to express and purify efficient rKOD in a commercial way.

Long-term preservation of eri and ailanthus silkworms using frozen gonads

Cryopreservation of eri and ailanthus silkworms using frozen gonads was investigated. First, we evaluated the freeze tolerance of ovary and testis in the eri silkworm, which showed high tolerance. Mating between frozen ovary-transplanted females and frozen testis-transplanted males produced 163.0 eggs, yielding 105.7 larvae per moth. In a second experiment, we tested the use of the eri silkworm as a host insect for gonad transplantation from ailanthus silkworm donors. A high success ratio for laid and hatched eggs was demonstrated for ovary transplantation (97.8 and 51.3 eggs per moth, respectively). For testis transplantation, however, the average number of hatched larvae was low (12.0). Mating between host eri females and males in which both frozen ovary and testis of the ailanthus silkworm had been transplanted produced 6.4 fertilized eggs per host moth. Our success in using cross subspecies cryopreservation between these wild silkworms could lead to the alternative use of hosts between species in other insects.

Molybdenum cofactor deficiency causes translucent integument, male-biased lethality, and flaccid paralysis in the silkworm Bombyx mori

Uric acid accumulates in the epidermis of Bombyx mori larvae and renders the larval integument opaque and white. Yamamoto translucent (oya) is a novel spontaneous mutant with a translucent larval integument and unique phenotypic characteristics, such as male-biased lethality and flaccid larval paralysis. Xanthine dehydrogenase (XDH) that requires a molybdenum cofactor (MoCo) for its activity is a key enzyme for uric acid synthesis. It has been observed that injection of a bovine xanthine oxidase, which corresponds functionally to XDH and contains its own MoCo activity, changes the integuments of oya mutants from translucent to opaque and white. This finding suggests that XDH/MoCo activity might be defective in oya mutants. Our linkage analysis identified an association between the oya locus and chromosome 23. Because XDH is not linked to chromosome 23 in B. mori, MoCo appears to be defective in oya mutants. In eukaryotes, MoCo is synthesized by a conserved biosynthesis pathway governed by four loci (MOCS1, MOCS2, MOCS3, and GEPH). Through a candidate gene approach followed by sequence analysis, a 6-bp deletion was detected in an exon of the B. mori molybdenum cofactor synthesis-step 1 gene (BmMOCS1) in the oya strain. Moreover, recombination was not observed between the oya and BmMOCS1 loci. These results indicate that the BmMOCS1 locus is responsible for the oya locus. Finally, we discuss the potential cause of male-biased lethality and flaccid paralysis observed in the oya mutants.

Identification of the silkworm quail gene reveals a crucial role of a receptor guanylyl cyclase in larval pigmentation

Diverse color patterns on the integument of lepidopteran larvae play important roles in their survival through camouflage, mimicry, sexual signaling, and aposematism. In the silkworm Bombyx mori, many color pattern variations have been preserved in inbred strains making them a good model for elucidating the molecular mechanisms that underlie color pattern formation. In this study, we focused on the silkworm quail (q) mutant, which exhibits abnormalities in multiple pigment biosynthesis pathways. Positional cloning of the q gene revealed that disruption of a guanylyl cyclase gene, BmGC-I, is responsible for its abnormal pigmentation. In q mutants, we identified a 16-bp deletion in the BmGC-I transcript, resulting in the production of a premature stop codon. Knockout of the BmGC-I gene resulted in the q-like abnormal pigmentation, thereby demonstrating that the BmGC-I gene is involved in the pigment biosynthesis pathway in the integument. Moreover, quantitative reverse transcription polymerase chain reaction showed that BmGC-I was strongly expressed in the fourth instar on day 2. Our results suggest that BmGC-I deficiency affects the pigment biosynthesis pathway, which supports the involvement of guanylyl cyclase in larval coloration.

Positional cloning of the sex-linked giant egg (Ge) locus in the silkworm, Bombyx mori

The giant egg (Ge) locus is a Z-linked mutation that leads to the production of large eggs. Cytological observations suggest that an unusual translocation of a large fragment of the W chromosome bearing a putative egg size-determining gene, Esd, gave rise to giant egg mutants. However, there is currently no molecular evidence confirming either a W-Z translocation or the presence of Esd on the W chromosome. To elucidate the origin of giant egg mutants, we performed positional cloning. We observed that the Bombyx mori. orthologue of the human Phytanoyl-CoA dioxygenase domain containing 1 gene (PHYHD1) is disrupted in giant egg mutants. PHYHD1 is highly conserved in eukaryotes and is predicted to be a Fe(II) and 2-oxoglutarate-dependent oxygenase. Exon skipping in one of the two available Ge mutants is probably caused by the insertion of a non-long terminal repeat transposon into intron 4 in the vicinity of the 5' splice site. Segmental duplication in Ge(2) , an independent allele, was caused by unequal recombination between short interspersed elements inserted into introns 3 and 5. Our results indicate that (1) Bombyx PHYHD1 is responsible for the Ge mutants and that (2) the Ge locus is unrelated to the W-linked putative Esd. To our knowledge, this is the first report describing the phenotypic defects caused by mutations in PHYHD1 orthologues.

Utility of Dry Gel from Two-dimensional Electrophoresis for Peptide Mass Fingerprinting Analysis of Silkworm Proteins

We compared the use of wet and dry two-dimensional electrophoresis (2-DE) gels for in-gel tryptic digestion and subsequent analysis by mass spectrometry, first using bovine serum albumin (BSA) as a model protein and then using unknown proteins from an extract of the silkworm midgut. The gel was either dried at 80 degrees C or left wet. Upon analysis of BSA, there was little difference in peptide recovery from 2-DE or in mass spectrum between the dry and the wet gels. The midgut extract was resolved into more than 1,100 protein spots by 2-DE, and 40 of these spots were sampled for further analysis. For all of the 40 proteins, the results obtained from dry and wet gels were quite similar in mass spectra and protein identification, although the relative amounts of peptides from tryptic digestion ranged from 45 to 146%. Based on these results, we confirmed the utility of dry electrophoretic gels for proteomics of insect extracts.

Proteomic Studies of Isoforms of the P25 Component ofBombyx moriFibroin

It is recognized that P25 is one of three polypeptide components of the fibroin synthesized in the larval silk gland (SG) of silkworm, having two glycosylated isoforms. In the present study, however, eight P25 isoforms were separated by proteomics, including two-dimensional gel electrophoresis of whole SG proteins, and were identified by the peptide mass fingerprinting method. Four of the eight isoforms were identified as Bombyx mandarina P25s, although the SG of Bombyx mori has never been considered to contain the P25 from B. mandarina. It is suggested that this diversity of P25 isoforms depends on phosphorylation modification in addition to glycosylation.

Genes Encoding Small Heat Shock Proteins of the Silkworm,Bombyx mori

Small heat shock protein (sHSP) is a family of ubiquitous polypeptides involved in a variety of physiological phenomena. From the silkworm, Bombyx mori, we isolated and sequenced the following cDNAs encoding sHSPs: shsp19.9, shsp20.1, shsp20.4, shsp20.8, shsp21.4, and shsp23.7. shsp21.4 was nearly twice as large in size as other shsps. The deduced amino acid sequence of sHSP21.4 was similar to that of Drosophila melanogaster CG14207-PA. Other sHSPs were highly similar to each other and, in a phylogenetic tree, formed a cluster including Plodia interpunctella alphaCP25. It was speculated that shsp21.4 has at least one intron in genome while other shsps do not. The transcripts of all shsps were subtle, but were constitutively detected in various tissues. Heat shock triggered a substantial increase in the transcripts other than shsp21.4. The B. mori sHSPs are perhaps classified into at least two groups: sHSP21.4 and others.

Expression and Characterization of a Sigma-Class Glutathione S-Transferase of the Fall Webworm,Hyphantria cunea

A cDNA encoding glutathione S-transferase (GST) of the fall webworm, Hyphantria cunea, was cloned by reverse transcriptase-polymerase chain reaction. The resulting clone (hcGST) was sequenced and deduced for amino acid sequence, which revealed 87, 59, and 42% identities to Sigma-class GSTs from Bombyx mori, Manduca sexta, and Blattella germanica respectively. A recombinant hcGST protein (rhcGST) was functionally overexpressed in Escherichia coli cells in a soluble form and purified to homogeneity. rhcGST retained more than 75% of its original GST activity after incubation at pHs 6 to 11. Incubation for 30 min at temperatures below 50 degrees C scarcely affected the activity. rhcGST was able to catalyze the reaction of glutathione with 1-chloro-2,4-dinitrobenzene, a universal substrate for GST, as well as with 4-hydroxynonenal, a product of lipid peroxidation. We also found that as compared to B. mori Sigma-class GST, rhcGST had a higher affinity for fenitrothion, an organophosphorus insecticide.

Proteomic Studies of Lipopolysaccharide-induced Polypeptides in the Silkworm,Bombyx mori

Silkworm larvae at the 5th instar were injected with lipopolysaccharide from Escherichia coli and inducible polypeptides were examined within a pI range of 3-10 and a size range of 14-97 kDa by proteomics, including peptide mass fingerprinting. No polypeptides were induced in the midgut. FB1 and H1-4 polypeptides were significantly induced in fat body and hemolymph, respectively. FB1 and H1 were estimated to be antitrypsin and serpin-2 proteinase inhibitors respectively. H2 and H3 were novel polypeptides. H4 was estimated to be attacin antibacterial polypeptide with high coverage of sequence. The amounts of all the induced polypeptides decreased at 48 h after the injection.

Superoxide Dismutase from the Silkworm,Bombyx mori: Sequence, Distribution, and Overexpression

Superoxide dismutase (SOD) is an enzyme facilitating the removal of superoxide anions from living organisms. This study focused on SOD from the silkworm, Bombyx mori (bmSOD). cDNA encoding bmSOD was amplified by reverse transcriptase-polymerase chain reaction. The deduced amino acid sequence of bmSOD indicated that the residues forming the Cu/Zn binding site are conserved and that the sequence is in 60% identity to that of the Drosophila melanogaster. B. mori SOD was also close to the D. melanogaster SOD in a phylogenetic tree. The bmSOD mRNA and the enzyme activity were widely distributed in diverse tissues. bmSOD functionally overexpressed in Escherichia coli in a soluble form was purified, and its stability was examined. bmSOD at 4 degrees C retained almost all of its original activity after incubation at pH 4-11 for 24 h. Incubation (pH 7) for 30 min at temperatures below 40 degrees C also affected activity insignificantly.

Purification and characterization of cocoonase from the silkworm Bombyx mori

Cocoonase (CCN) which facilitates the degradation of a cocoon is recognized as a trypsin-like serine protease. In this study, CCN from the silkworm Bombyx mori was purified and comprehensively characterized. Its activity was maximal at about pH 9.8. It was stable above pH 3.4 at 4 °C and below 50 °C at pH 7.5. CuSO4, FeSO4, and ZnSO4 showed inhibitory effects on CCN, but other salts improved activity. Typical trypsin inhibitors inhibited CCN, but the relative inhibitory activities were much lower than those against bovine trypsin. An extract of cocoon shells inhibited trypsin, but it was only slightly inhibitory against CCN. There were significant differences in catalytic efficiencies and substrate specificities as between CCN and bovine trypsin.

Identification of key uric acid synthesis pathway in a unique mutant silkworm Bombyx mori model of Parkinson's disease

Plasma uric acid (UA) levels decrease following clinical progression and stage development of Parkinson’s disease (PD). However, the molecular mechanisms underlying decreases in plasma UA levels remain unclear, and the potential to apply mutagenesis to a PD model has not previously been discovered. We identified a unique mutant of the silkworm Bombyx mori (B.mori) op. Initially, we investigated the causality of the phenotypic “op” by microarray analysis using our constructed KAIKO functional annotation pipeline. Consequently, we found a novel UA synthesis-modulating pathway, from DJ-1 to xanthine oxidase, and established methods for large-scale analysis of gene expression in B. mori. We found that the mRNA levels of genes in this pathway were significantly lower in B. mori op mutants, indicating that downstream events in the signal transduction cascade might be prevented. Additionally, levels of B.mori tyrosine hydroxylase (TH) and DJ-1 mRNA were significantly lower in the brain of B. mori op mutants. UA content was significantly lower in the B. mori op mutant tissues and hemolymph. The possibility that the B. mori op mutant might be due to loss of DJ-1 function was supported by the observed vulnerability to oxidative stress. These results suggest that UA synthesis, transport, elimination and accumulation are decreased by environmental oxidative stress in the B. mori op mutant. In the case of B. mori op mutants, the relatively low availability of UA appears to be due both to the oxidation of DJ-1 and to its expenditure to mitigate the effects of environmental oxidative stress. Our findings are expected to provide information needed to elucidate the molecular mechanism of decreased plasma UA levels in the clinical stage progression of PD.

Albino (al) is a tetrahydrobiopterin (BH4)-deficient mutant of the silkworm Bombyx mori

Albino (al) is a lethal mutant of Bombyx mori that exhibits a colourless cuticle after the first ecdysis and dies without feeding on mulberry. Previous studies have indicated that sclerotisation was insufficient because of defective phenylalanine and tyrosine metabolism in albino larvae. However, the genetic mechanism underlying the albino phenotype has not been determined. Dopamine plays a central role in insect cuticle colouration and sclerotisation. The pathway for dopamine biosynthesis from phenylalanine involves phenylalanine hydroxylase (PAH; EC 1.14.16.1) and tyrosine hydroxylase (TH; EC 1.14.16.2). Tetrahydrobiopterin (BH4) is an essential cofactor of aromatic amino acid hydroxylases, including PAH and TH. Thus, BH4 is indispensable for cuticle colouration and sclerotisation. Here we report on identifying mutations in the gene that encodes for the Bombyx homolog of 6-pyruvoyl-tetrahydropterin synthase (PTS) which is involved in the biosynthesis of BH4, in 2 strains with different al alleles. In strain a60 (al), a transposable element was inserted in exon 2 of BmPTS. In strain a61 (al²), an 11-bp deletion was identified in the exon 2 region of BmPTS. After oral administration of BH4 to the al² larvae, the survival rate was effectively increased and the larval integument was pigmented. These results indicated that BmPTS was responsible for the albino mutants of B. mori. We conclude that (i) a mutation in BmPTS leads to an insufficient supply of BH4 and results in defective dopamine biosynthesis and (ii) lack of dopamine results in cuticle colouration and sclerotisation failure. Lemon (lem) is a BH4-deficient mutant. It has been reported that de novo synthesis of zygotic BH4 was indispensable for viability of the embryo in eggs laid by lem (lem/lem¹) females. We found that lem/lem, al²/al² larvae produced by lem (lem/lem) females were viable during the first instar stage, suggesting that al²/al² embryo could synthesis BH4 by using maternally transmitted BmPTS.

Mutation of a novel ABC transporter gene is responsible for the failure to incorporate uric acid in the epidermis of ok mutants of the silkworm, Bombyx mori

ok mutants of the silkworm, Bombyx mori, exhibit highly translucent larval skin resulting from the inability to incorporate uric acid into the epidermal cells. Here we report the identification of a gene responsible for the ok mutation using positional cloning and RNAi experiments. In two independent ok mutant strains, we found a 49-bp deletion and a 233-bp duplication, respectively, in mRNAs of a novel gene, Bm-ok, which encodes a half-type ABC transporter, each of which results in translation of a truncated protein in each mutant. Although the Bm-ok sequence was homologous to well-known transporter genes, white, scarlet, and brown in Drosophila, the discovery of novel orthologs in the genomes of lepidopteran, hymenopteran, and hemipteran insects identifies it as a member of a new distinct subfamily of transporters. Embryonic RNAi of Bm-ok demonstrated that repression of Bm-ok causes a translucent phenotype in the first-instar silkworm larva. We discuss the possibility that Bm-ok forms a heterodimer with another half-type ABC transporter, Bmwh3, and acts as a uric acid transporter in the silkworm epidermis.

Vitellogenin receptor mutation leads to the oogenesis mutant phenotype "scanty vitellin" of the silkworm, Bombyx mori

In insects, the vitellogenin receptor (VgR) mediates the uptake of vitellogenin (Vg) from the hemolymph by developing oocytes. The oogenesis mutant scanty vitellin (vit) of Bombyx mori (Bm) lacks vitellin and 30-kDa proteins, but B. mori egg-specific protein and BmVg are normal. The vit eggs are white and smaller compared with the pale yellow eggs of the wild type and are embryonic lethal. This study found that a mutation in the B. mori VgR gene (BmVgR) is responsible for the vit phenotype. We cloned the cDNA sequences encoding WT and vit BmVgR. The functional domains of BmVgR are similar to those of other low-density lipoprotein receptors. When compared with the wild type, a 235-bp genomic sequence in vit BmVgR is substituted for a 7-bp sequence. This mutation has resulted in a 50-amino acid deletion in the third Class B region of the first epidermal growth factor (EGF1) domain. BmVgR is expressed specifically in oocytes, and the transcriptional level is changed dramatically and consistently with maturation of oocytes during the previtellogenic periods. Linkage analysis confirmed that BmVgR is mutated in the vit mutant. The coimmunoprecipitation assay confirmed that mutated BmVgR is able to bind BmVg but that BmVg cannot be dissociated under acidic conditions. The WT phenotype determined by RNA interference was similar to that of the vit phenotype for nutritional deficiency, such as BmVg and 30-kDa proteins. These results showed that BmVgR has an important role in transporting proteins for egg formation and embryonic development in B. mori.

Reduced expression of the dysbindin-like gene in the Bombyx mori ov mutant exhibiting mottled translucency of the larval skin

The ov (mottled translucent of Var) mutant, an oily mutant of Bombyx mori, exhibits mottled translucent skin with a varying degree of transparency among individuals. By linkage analysis of 2112 backcross individuals using polymorphic DNA markers, we successfully mapped a 179-kb region of chromosome 20 responsible for the ov phenotype. This region contains nine predicted genes. We compared the mRNA expression of these nine genes between the wild type and mutants and found that the expression of one of them, Bmdysb, was strikingly decreased in the epidermis of ov as well as its allelomorph, ovp. Moreover, its expression level was well correlated with the degree of transparency among individuals. Bmdysb was homologous to DTNBP1 encoding human dysbindin, a subunit of the biogenesis of lysosome-related organelles complex-1. Our results suggest that the translucent skin may be due to repression of Bmdysb in the ov mutants and that Bmdysb plays an important role in the formation and accumulation of urate granules in the silkworm epidermis.

CD36 homolog divergence is responsible for the selectivity of carotenoid species migration to the silk gland of the silkworm Bombyx mori

Dietary carotenoids are absorbed in the intestine and delivered to various tissues by circulating lipoproteins; however, the mechanism underlying selective delivery of different carotenoid species to individual tissues remains elusive. The products of the Yellow cocoon (C) gene and the Flesh (F) gene of the silkworm Bombyx mori determine the selectivity for transport of lutein and β-carotene, respectively, to the silk gland. We previously showed that the C gene encodes Cameo2, a CD36 family member, which is thought to function as a transmembrane lipoprotein receptor. Here, we elucidated the molecular identity of the F gene product by positional cloning, as SCRB15, a paralog of Cameo2 with 26% amino acid identity. In the F mutant, SCRB15 mRNA structure was severely disrupted, due to a 1.4 kb genomic insertion in a coding exon. Transgenic expression of SCRB15 in the middle silk gland using the binary GAL4-UAS expression system enhanced selective β-carotene uptake by the middle silk gland, while transgenic expression of Cameo2 enhanced selective lutein uptake under the same GAL4 driver. Our findings indicate that divergence of genes in the CD36 family determines the selectivity of carotenoid species uptake by silk gland tissue and that CD36-homologous proteins can discriminate among carotenoid species.

Phylogeny and evolutionary history of the silkworm

The silkworm, Bombyx mori, played an important role in the old Silk Road that connected ancient Asia and Europe. However, to date, there have been few studies of the origins and domestication of this species using molecular methods. In this study, DNA sequences of mitochondrial and nuclear loci were used to infer the phylogeny and evolutionary history of the domesticated silkworm and its relatives. All of the phylogenetic analyses indicated a close relationship between the domesticated silkworm and the Chinese wild silkworm. Domestication was estimated to have occurred about 4100 years ago (ya), and the radiation of the different geographic strains of B. mori about 2000 ya. The Chinese wild silkworm and the Japanese wild silkworm split about 23600 ya. These estimates are in good agreement with the fossil evidence and historical records. In addition, we show that the domesticated silkworm experienced a population expansion around 1000 ya. The divergence times and the population dynamics of silkworms presented in this study will be useful for studies of lepidopteran phylogenetics, in the genetic analysis of domestic animals, and for understanding the spread of human civilizations.

Identification of the Bombyx red egg gene reveals involvement of a novel transporter family gene in late steps of the insect ommochrome biosynthesis pathway

Ommochromes are one of the major pigments involved in coloration of eggs, eyes, and body surface of insects. However, the molecular mechanisms of the final steps of ommochrome pigment synthesis have been largely unknown. The eggs of the silkworm Bombyx mori contain a mixture of ommochrome pigments, and exhibit a brownish lilac color. The recessive homozygous of egg and eye color mutant, red egg (re), whose eggs display a pale orange color instead of normal dark coloration, has been long suggested to have a defect in the biosynthesis of the final ommochrome pigments. Here, we identify the gene responsible for the re locus by positional cloning, mutant analysis, and RNAi experiments. In the re mutants, we found that a 541-bp transposable element is inserted into the ORF of BGIBMGA003497-1 (Bm-re) encoding a novel member of a major facilitator superfamily transporter, causing disruption of the splicing of exon 9, resulting in two aberrant transcripts with frameshifts yielding nonfunctional proteins lacking the C-terminal transmembrane domains. Bm-re function in pigmentation was confirmed by embryonic RNAi experiments. Homologs of the Bm-re gene were found in all insect genomes sequenced at present, except for 12 sequenced Drosophila genomes, which seemed to correlate with the previous studies that have demonstrated that eye ommochrome composition is different from other insects in several Dipterans. Knockdown of the Bm-re homolog by RNAi in the red flour beetle Tribolium castaneum caused adult compound eye coloration defects, indicating a conserved role in ommochrome pigment biosynthesis at least among holometabolous insects.

Precocious metamorphosis in the juvenile hormone-deficient mutant of the silkworm, Bombyx mori

Insect molting and metamorphosis are intricately governed by two hormones, ecdysteroids and juvenile hormones (JHs). JHs prevent precocious metamorphosis and allow the larva to undergo multiple rounds of molting until it attains the proper size for metamorphosis. In the silkworm, Bombyx mori, several “moltinism” mutations have been identified that exhibit variations in the number of larval molts; however, none of them have been characterized molecularly. Here we report the identification and characterization of the gene responsible for the dimolting (mod) mutant that undergoes precocious metamorphosis with fewer larval–larval molts. We show that the mod mutation results in complete loss of JHs in the larval hemolymph and that the mutant phenotype can be rescued by topical application of a JH analog. We performed positional cloning of mod and found a null mutation in the cytochrome P450 gene CYP15C1 in the mod allele. We also demonstrated that CYP15C1 is specifically expressed in the corpus allatum, an endocrine organ that synthesizes and secretes JHs. Furthermore, a biochemical experiment showed that CYP15C1 epoxidizes farnesoic acid to JH acid in a highly stereospecific manner. Precocious metamorphosis of mod larvae was rescued when the wild-type allele of CYP15C1 was expressed in transgenic mod larvae using the GAL4/UAS system. Our data therefore reveal that CYP15C1 is the gene responsible for the mod mutation and is essential for JH biosynthesis. Remarkably, precocious larval–pupal transition in mod larvae does not occur in the first or second instar, suggesting that authentic epoxidized JHs are not essential in very young larvae of B. mori. Our identification of a JH–deficient mutant in this model insect will lead to a greater understanding of the molecular basis of the hormonal control of development and metamorphosis.

The number of larval instars in insects varies greatly across insect taxa and can even vary at the intraspecific level. However, little is known about how the number of larval instars is fixed in each species or modified by the environment. The silkworm, Bombyx mori, provides a unique bioresource for investigating this question, as there are several “moltinism” strains that exhibit variations in the number of larval molts. The present study describes the first positional cloning of a moltinism gene. We performed genetic and biochemical analyses on the dimolting (mod) mutant, which shows precocious metamorphosis with fewer larval–larval molts. We found that mod is a juvenile hormone (JH)–deficient mutant that is unable to synthesize JH, a hormone that prevents precocious metamorphosis and allows the larvae to undergo multiple rounds of larval–larval molts. This JH–deficient mutation is the first described to date in any insect species and, therefore, the mod strain will serve as a useful model for elucidating the molecular mechanism of JH action. Remarkably, precocious larval–pupal transition in mod larvae does not occur in the first or second instar, suggesting that morphostatic action of JH is not necessary for young larvae of B. mori.

Mutations in an amino acid transporter gene are responsible for sex-linked translucent larval skin of the silkworm, Bombyx mori

The sex-linked translucent (os) mutation in the silkworm, Bombyx mori, confers slightly translucent larval skin resulting from a decrease in the incorporation of uric acid into epidermal cells. By positional cloning, we narrowed a region linked to the os phenotype to approximately 157 kb located on scaffold Bm_scaf72 on the Z chromosome (chromosome 1). The region contained four gene models. Sequencing analysis revealed that one of the candidate genes had a 7-bp deletion in the coding region. We also found a 111-bp deletion or single-nucleotide substitution in the same gene using independent os mutant strains. Because all the mutations caused the generation of abnormal transcripts followed by translation of a truncated protein, we conclude that the mutation of this candidate gene is responsible for the translucent larval skin of the os mutant. Sequence analysis indicated that the gene responsible for the os mutation had homology to amino acid transporters of the solute carrier family of proteins. Our results suggest that solute carrier proteins are involved in uric acid transport in insects and other invertebrates.

Characterization of an omega-class glutathione S-transferase in the stress response of the silkmoth

The glutathione S-transferase (GST) superfamily is involved in detoxification of various xenobiotics. Using real-time PCR, mRNA encoding an omega-class GST of Bombyx mori (bmGSTO) was shown to be induced after exposure to various environmental stresses. A soluble form of recombinant protein (rbmGSTO) was functionally overexpressed in Escherichia coli cells and purified to homogeneity. Cys 38 and Pro 39 were found to be highly conserved in omega-class GSTs, and their roles were investigated by site-directed mutagenesis/kinetic analysis. Mutations of Cys 38 and Pro 39 residues affected the catalytic efficiency of enzymes, indicating that the presence of Cys 38 and Pro 39 residues is important for bmGSTO activity. Thus, bmGSTO could contribute to increasing the environmental stress resistance of lepidopteran insects.

BmDJ-1 is a key regulator of oxidative modification in the development of the silkworm, Bombyx mori

We cloned cDNA for the Bombyx mori DJ-1 protein (BmDJ-1) from the brains of larvae. BmDJ-1 is composed of 190 amino acids and encoded by 672 nucleotides. Northern blot analysis showed that BmDJ-1 is transcribed as a 756-bp mRNA and has one isoform. Reverse transcriptase (RT)-PCR experiments revealed that the BmDJ-1 was present in the brain, fatbody, Malpighian tubule, ovary and testis but present in only low amounts in the silkgland and hemocyte of day 4 fifth instar larvae. Immunological analysis demonstrated the presence of BmDJ-1 in the brain, midgut, fatbody, Malpighian tubule, testis and ovary from the larvae to the adult. We found that BmDJ-1 has a unique expression pattern through the fifth instar larval to adult developmental stage. We assessed the anti-oxidative function of BmDJ-1 using rotenone (ROT) in day 3 fifth instar larvae. Administration of ROT to day 3 fifth instar larvae, together with exogenous (BmNPV-BmDJ-1 infection for 4 days in advance) BmDJ-1, produced significantly lower 24-h mortality in BmDJ-1 groups than in the control. 2D-PAGE revealed an isoelectric point (pI) shift to an acidic form for BmDJ-1 in BmN4 cells upon ROT stimulus. Among the factors examined for their effects on expression level of BmDJ-1 in the hemolymph, nitric oxide (NO) concentration was identified based on dramatic developmental stage-dependent changes. Administration of isosorbide dinitrate (ISDN), which is an NO donor, to BmN4 cells produced increased expression of BmDJ-1 compared to the control. These results suggest that BmDJ-1 might control oxidative stress in the cell due to NO and serves as a development modulation factor in B. mori.

Molecular defect of isovaleryl-CoA dehydrogenase in the skunk mutant of silkworm, Bombyx mori

The isovaleric acid-emanating silkworm mutant skunk (sku) was first studied over 30 years ago because of its unusual odour and prepupal lethality. Here, we report the identification and characterization of the gene responsible for the sku mutant. Because of its specific features and symptoms similar to human isovaleryl-CoA dehydrogenase (IVD) deficiency, also known as isovaleric acidaemia, IVD dysfunction in silkworms was predicted to be responsible for the phenotype of the sku mutant. Linkage analysis revealed that the silkworm IVD gene (BmIVD) was closely linked to the odorous phenotype as expected, and a single amino acid substitution (G376V) was found in BmIVD of the sku mutant. To investigate the effect of the G376V substitution on BmIVD function, wild-type and sku-type recombinants were constructed with a baculovirus expression system and the subsequent enzyme activity of sku-type BmIVD was shown to be significantly reduced compared with that of wild-type BmIVD. Molecular modelling suggested that this reduction in the enzyme activity may be due to negative effects of G376V mutation on FAD-binding or on monomer-monomer interactions. These observations strongly suggest that BmIVD is responsible for the sku locus and that the molecular defect in BmIVD causes the characteristic smell and prepupal lethality of the sku mutant. To our knowledge, this is, aside from humans, the first characterization of IVD deficiency in metazoa. Considering that IVD acts in the third step of leucine degradation and the sku mutant accumulates branched-chain amino acids in haemolymph, this mutant may be useful in the investigation of unique branched-chain amino acid catabolism in insects.

Transgenic analysis of the BmBLOS2 gene that governs the translucency of the larval integument of the silkworm, Bombyx mori

The larval integument of the silkworm, Bombyx mori, is opaque because urate granules accumulate in the epidermis. Although the biosynthetic pathway of uric acid is well studied, little is known about how uric acid accumulates as urate granules in epidermal cells. In the distinct oily (od) mutant silkworm, the larval integument is translucent because of the inability to construct urate granules. Recently, we have found that the od mutant has a genomic deletion in the B. mori homologue of the human biogenesis of lysosome-related organelles complex1, subunit 2 (BLOS2) gene (BmBLOS2). Here, we performed a molecular and functional characterization of BmBLOS2. Northern blot analysis showed that BmBLOS2 was ubiquitously expressed in various tissues. We analysed the structure of a newly isolated mutant (od(B) ) allelic to od and found a premature stop codon in the coding sequence of BmBLOS2 in this new mutation. Moreover, the translucent phenotype was rescued by the germ-line transformation of the wild-type BmBLOS2 allele into the od mutant. Our results suggest that BmBLOS2 is responsible for the od mutant phenotype and plays a crucial role in biogenesis of urate granules in the larval epidermis of the silkworm. The relationships amongst Hermansky-Pudlak syndrome (HPS) genes in mammals, granule group genes in Drosophila and translucent mutant genes in B. mori are discussed.

The silkworm-an attractive BioResource supplied by Japan

Silkworms have played an important agricultural role in supporting Japan's modernization, and traditionally, Japan has led the world as a repository of silkworm bioresources. The silkworm is a small and highly domesticated insect, which is ideal as a laboratory tool, although it is a bioresource that is relatively infrequently used in experiments at present. In this review, we describe the potential for silkworm resources to contribute to life sciences.

Non-molting glossy/shroud encodes a short-chain dehydrogenase/reductase that functions in the 'Black Box' of the ecdysteroid biosynthesis pathway

In insects, the precise timing of molting and metamorphosis is strictly guided by a principal steroid hormone, ecdysone. Among the multiple conversion steps for synthesizing ecdysone from dietary cholesterol, the conversion of 7-dehydrocholesterol to 5beta-ketodiol, the so-called 'Black Box', is thought to be the important rate-limiting step. Although a number of genes essential for ecdysone synthesis have recently been revealed, much less is known about the genes that are crucial for functioning in the Black Box. Here we report on a novel ecdysteroidgenic gene, non-molting glossy (nm-g)/shroud (sro), which encodes a short-chain dehydrogenase/reductase. This gene was first isolated by positional cloning of the nm-g mutant of the silkworm Bombyx mori, which exhibits a low ecdysteroid titer and consequently causes a larval arrest phenotype. In the fruit fly, Drosophila melanogaster, the closest gene to nm-g is encoded by the sro locus, one of the Halloween mutant members that are characterized by embryonic ecdysone deficiency. The lethality of the sro mutant is rescued by the overexpression of either sro or nm-g genes, indicating that these two genes are orthologous. Both the nm-g and the sro genes are predominantly expressed in tissues producing ecdysone, such as the prothoracic glands and the ovaries. Furthermore, the phenotypes caused by the loss of function of these genes are restored by the application of ecdysteroids and their precursor 5beta-ketodiol, but not by cholesterol or 7-dehydrocholesterol. Altogether, we conclude that the Nm-g/Sro family protein is an essential enzyme for ecdysteroidogenesis working in the Black Box.

A CD36-related transmembrane protein is coordinated with an intracellular lipid-binding protein in selective carotenoid transport for cocoon coloration

The transport pathway of specific dietary carotenoids from the midgut lumen to the silk gland in the silkworm, Bombyx mori, is a model system for selective carotenoid transport because several genetic mutants with defects in parts of this pathway have been identified that manifest altered cocoon pigmentation. In the wild-type silkworm, which has both genes, Yellow blood (Y) and Yellow cocoon (C), lutein is transferred selectively from the hemolymph lipoprotein to the silk gland cells where it is accumulated into the cocoon. The Y gene encodes an intracellular carotenoid-binding protein (CBP) containing a lipid-binding domain known as the steroidogenic acute regulatory protein-related lipid transfer domain. Positional cloning and transgenic rescue experiments revealed that the C gene encodes Cameo2, a transmembrane protein gene belonging to the CD36 family genes, some of which, such as the mammalian SR-BI and the fruit fly ninaD, are reported as lipoprotein receptors or implicated in carotenoid transport for visual system. In C mutant larvae, Cameo2 expression was strongly repressed in the silk gland in a specific manner, resulting in colorless silk glands and white cocoons. The developmental profile of Cameo2 expression, CBP expression, and lutein pigmentation in the silk gland of the yellow cocoon strain were correlated. We hypothesize that selective delivery of lutein to specific tissue requires the combination of two components: 1) CBP as a carotenoid transporter in cytosol and 2) Cameo2 as a transmembrane receptor on the surface of the cells.

NBRP databases: databases of biological resources in Japan

The National BioResource Project (NBRP) is a Japanese project that aims to establish a system for collecting, preserving and providing bioresources for use as experimental materials for life science research. It is promoted by 27 core resource facilities, each concerned with a particular group of organisms, and by one information center. The NBRP database is a product of this project. Thirty databases and an integrated database-retrieval system (BioResource World: BRW) have been created and made available through the NBRP home page (http://www.nbrp.jp). The 30 independent databases have individual features which directly reflect the data maintained by each resource facility. The BRW is designed for users who need to search across several resources without moving from one database to another. BRW provides access to a collection of 4.5-million records on bioresources including wild species, inbred lines, mutants, genetically engineered lines, DNA clones and so on. BRW supports summary browsing, keyword searching, and searching by DNA sequences or gene ontology. The results of searches provide links to online requests for distribution of research materials. A circulation system allows users to submit details of papers published on research conducted using NBRP resources.