Proteotranscriptomic Integration analyses reveals new mechanistic insights regarding Bombyx mori fluorosis

The commercial value of silkworms has been widely explored and the effects of fluoride exposure on silkworms' breeding and silk production cannot be ignored. Bombyx mori is a commonly used model to explore the mechanisms of fluorosis. In the present study, we analyzed the differences in physiological and biochemical indicators after exposing larva to NaF, then evaluated differential genes and proteins. Compared to control, larvae exposed to 600 mg L^-1 NaF presented decreased bodyweight, damaged midgut tissue, and were accompanied by oxidative stress. The RNA-seq showed 1493 differentially expressed genes (574 upregulated and 919 downregulated). Meanwhile, the TMT detected 189 differentially expressed proteins (133 upregulated and 56 downregulated). The integrative analysis led to 4 upregulated and 9 downregulated genes and proteins. Finally, we hypothesized that fluoride exposure might affect the intestinal digestion of silkworms, inhibit the gene expression of detoxification enzymes and stimulate cellular immune responses. Our current findings provided new insights into insect fluorosis.

Bombyx mori Vps13d is a key gene affecting silk yield

Bombyx mori is an important economic insect, its economic value mainly reflected in the silk yield. The major functional genes affecting the silk yield of B. mori have not been determined yet. Bombyx mori vacuolar protein sorting-associated protein 13d (BmVps13d) has been identified, but its function is not reported. In this study, BmVps13d protein shared 30.84% and 34.35% identity with that of in Drosophila melanogaster and Homo. sapiens, respectively. The expressions of BmVps13d were significantly higher in the midgut and silk gland of JS (high silk yield) than in that of L10 (low silk yield). An insertion of 9 bp nucleotides and two deficiencies of adenine ribonucleotides in the putative promoter region of BmVps13d gene in L10 resulted in the decline of promoter activity was confirmed using dual luciferase assay. Finally, the functions of BmVps13d in B. mori were studied using the CRISPR/Cas9 system, and the mutation of BmVps13d resulted in a 24.7% decline in weight of larvae, as well as a 27.1% (female) decline and a 11.8% (male) decline in the silk yield. This study provides a foundation for studying the molecular mechanism of silk yield and breeding the silkworm with high silk yield.

Geminin is essential for DNA re-replication in the silk gland cells of silkworms

Endoreplication, known as endocycles or endoreduplication, is a cell cycle variant in which the genomic DNA is re-replicated without mitosis leading to polyploidy. Endoreplication is essential for the development and functioning of the different organs in animals and plants. Deletion of Geminin, a DNA replication licensing inhibitor, causes DNA re-replication or damage. However, the role of Geminin in endoreplication is still unclear. Here, we studied the role of Geminin in the endoreplication of the silk gland cells of silkworms by constructing two transgenic silkworm strains, including BmGeminin1-overexpression and BmGeminin1-RNA interference. Interference of BmGeminin1 led to body weight gain, increased silk gland volume, increased DNA content, and enhanced DNA re-replication activity relative to wild-type Dazao. Meanwhile, overexpression of BmGeminin1 showed an opposite phenotype compared to the BmGem1-RNAi strain. Furthermore, RNA-sequencing of the transgenic strains was carried out to explore how BmGeminin1 regulates DNA re-replication. Our data demonstrated a vital role of Geminin in the regulation of endoreplication in the silk gland of silkworms.

Sage controls silk gland development by regulating Dfd in Bombyx mori

Silk gland is an organ that produces and secretes silk proteins. The development of the silk gland is essential for high silk production yield and silk quality. Although Sage reportedly plays a pivotal role in embryonic silk gland development, the mechanism underlying its action remains unclear. Our study aimed to determine the genes downstream of Sage through which it regulates the development of the silk gland. After chromatin immunoprecipitation and sequencing, Dfd was identified as a downstream target gene of Sage and it was confirmed that Sage could inhibit Dfd expression by competing with SGF1. When Dfd was knocked down through RNA interference (RNAi), the number of cells in the middle silk gland decreased, and the posterior silk gland was straightened. Simultaneously, the expression of Ser1 and silk fibroin genes was no longer strictly regional. These changes eventually led to an alteration in the composition of the Dfd RNAi cocoon. In conclusion, our research contributes to a deeper understanding of the development of silk glands.

Enhanced silk yield in transgenic silkworm (Bombyx mori) via ectopic expression of BmGT1-L in the posterior silk gland

The silkworm is an economically important insect producing plentiful silk fibre in the silk gland. In this study, we reported a cross-talk between the fat body, silk gland and midgut through a glycine-serine biosynthetic pathway in the silkworm. Amino acid sequence and functional domains of glycine transporter gene BmGT1-L were mapped. Our results indicated that BmGT1-L was specifically expressed in the midgut microvilli and persistently expressed during the feeding stages. RNA interference of BmGT1-L activated glycine biosynthesis, and BmGT1-L overexpression facilitated serine biosynthesis in the BmN4-SID1 cell. In addition, silkworms after FibH gene knock-out or silk gland extirpation showed markedly decreased BmGT1-L transcripts in the midgut and disturbed glycine-serine biosynthesis as silk yield decreased. Finally, BmGT1-L ectopic expression in the posterior silk gland promoted glycine biosynthesis, and enhanced silk yield via increasing fibroin synthesis. These results suggested that cross-talk between tissues can be used for enhancing silk yield in the silkworm.

Effect of pyriproxyfen exposure on cocooning and gene expression in the silk gland of Bombyx mori （Linnaeus, 1758）

Bombyx mori（Linnaeus, 1758） is an important economical insect, and the sericulture is a flourishing industry in many developing countries. Pyriproxyfen, a juvenile hormone pesticide, is often applied to cultivations widely in the world, and its exposure often resulted in silk yield reduction and non-cocooning. However, the effect of pyriproxyfen exposure on cocooning and gene expression level in the silk gland of B. mori has not been studied yet, and this study focused on the above issues. The result indicated that pyriproxyfen exposure can lead to silk gland injury, reduction of silk yield and cocooning rate. Furthermore, the expression levels of silk protein synthesis related genes were down regulated significantly. The same change trends were shown between PI3K/Akt and CncC/Keap1 pathway, which is the expressions of key genes can be elevated by pyriproxyfen exposure. In addition, the activity of detoxification enzymes (P450, GST and CarE) and the expression levels of detoxification genes were elevated after pyriproxyfen exposure, suggesting that detoxification enzymes may play an important role in detoxification of pyriproxyfen in silk gland. These results provided possible clues to the silk gland injury and gene transcriptional level changes in silkworm after pyriproxyfen exposure.

Photoelectric Silk via Genetic Encoding and Bioassisted Plasmonics

Genetically encoded photoelectric silk that can convert photons to electrons (light to electricity) over a wide visible range in a self-power mode is reported. As silk is a versatile host material with electrical conductivity, biocompatibility, and processability, a photoelectric protein is genetically fused with silk by silkworm transgenesis. Specifically, mKate2, which is conventionally known as a far-red fluorescent protein, is used as a photoelectric protein. Characterization of the electrochemical and optical properties of mKate2 silk allows designing a photoelectric measurement system. A series of in situ photocurrent experiments support the sensitive and stable performance of photoelectric conversion. In addition, as a plasmonic nanomaterial with a broad spectral resonance, titanium nitride (TiN) nanoparticles are biologically hybridized into the silk glands, taking full advantage of the silkworms' open circulatory system as well as the absorption band of mKate2 silk. This biological hybridization via direct feeding of TiN nanoparticles further enhances the overall photoelectric conversion ability of mKate2 silk. It is envisioned that the biologically derived photoelectric protein, its ecofriendly scalable production by transgenic silkworms, and the bioassisted plasmonic hybridization can potentially broaden the biomaterial choices for developing next-generation biosensing, retina prosthesis, and neurostimulation applications.

Hers and his: Silk glands used in egg sac construction by female spiders potentially repurposed by a 'modern' male spider

Cylindrical silk gland (CY) spigots distinguish a large clade of modern spiders, the CY spigot clade, which includes all entelegyne spiders and their closest relatives. Following a widespread paradigm, CYs and their spigots are only known to occur in female spiders and they produce silk used in the construction of egg sacs. Here we report the occurrence of a CY spigot or CY nubbin on each posterior median spinneret (PMS) in males (5th stadium and later) of the spider Australomimetus maculosus. Late juvenile males had a CY spigot on each PMS, whereas adult males either had a CY spigot or, more often, a non-functional CY nubbin. This indicates that potential CY use by males is at least largely limited to late juvenile instars and is not involved with egg sac construction. Despite the presence of CY spigots in both sexes, sexual dimorphism with respect to CYs was still evident since males lacked the CY spigot on each posterior lateral spinneret present in late juvenile and adult females, and CY spigots of males never had the wide shaft and opening of adult females. This study adds to our knowledge of spinning apparatus variability in modern spiders and demonstrates an exception to the paradigm that, in the CY spigot clade, such spigots are restricted to female spiders.

Spider Silk for Tissue Engineering Applications

Due to its properties, such as biodegradability, low density, excellent biocompatibility and unique mechanics, spider silk has been used as a natural biomaterial for a myriad of applications. First clinical applications of spider silk as suture material go back to the 18th century. Nowadays, since natural production using spiders is limited due to problems with farming spiders, recombinant production of spider silk proteins seems to be the best way to produce material in sufficient quantities. The availability of recombinantly produced spider silk proteins, as well as their good processability has opened the path towards modern biomedical applications. Here, we highlight the research on spider silk-based materials in the field of tissue engineering and summarize various two-dimensional (2D) and three-dimensional (3D) scaffolds made of spider silk. Finally, different applications of spider silk-based materials are reviewed in the field of tissue engineering in vitro and in vivo.

Novaluron impairs the silk gland and productive performance of silkworm Bombyx mori (Lepidoptera: Bombycidae) larvae

This study investigates the effects of the insect growth regulator Novaluron on the silk gland (SG) and silk cocoon production in a nontarget insect, the silkworm Bombyx mori, which is a model research insect among Lepidoptera and of great economic importance for the commercial production of silk threads. Larvae were segregated into experimental groups: the control group (CG) and the treatment group (TG), which was exposed to a Novaluron concentration of 0.15 mL/L. Following exposure, we analyzed the cytotoxic effects on the epithelial cells of the anterior, middle and posterior regions of the SG of B. mori larvae in the 3rd, 4th, and 5th instars, as well as the quality of the cocoons from larvae in the 5th instar. Cytotoxic effects were observed in the TG, such as the dilation of cells, emission of cytoplasmic protrusions, extreme rarefaction of the cytoplasm and nuclei, dilation of the endoplasmic reticulum, intracellular and intercellular spaces, spacing between the epithelial cells and the basal lamina and detachment of some cells towards the lumen of the SG, and decreased protein in the lumen, with faults in its composition. In addition, we verified ultrastructural changes in the production of fibers and silk cocoons, including a reduction in the weight of the cocoons constructed by both males and females in the TG and the construction of defective cocoons. Novaluron exposure impairs the SG and may affect the physiological functions of this organ; additionally, it compromises the quality of silk cocoons, potentially causing serious damage to sericulture.

Bmsage is involved in the determination of cell number in the silk gland of Bombyx mori

The number of cells in tissues is under strict genetic control, and research on the determination of cell number is of great importance to understand the growth and development of organs. Bmsage, a bHLH transcription factor, is involved in the development of the silk gland during the embryonic stage in Bombyx mori. However, the mechanism by which it influences silk gland development is unclear. In the present study, we determined via immunofluorescence staining during the embryonic stage of Bombyx mori that Bmsage is expressed in silk gland cells from the beginning of development of the silk gland until its complete formation. By comparing different silkworm strains, we found that Bmsage expression is positively correlated with the number of silk gland cells. Bmsage knockdown by RNAi resulted in shorter silk glands and lower cell numbers, especially in the posterior silk gland. The silk gland lumen also shriveled, and the silk protein content was significantly lower than that in the control. Further investigation revealed that all cyclins decreased after knock down of Bmsage, and cyclin B and cyclin 3 were significantly down-regulated. Bmsage may be involved in the regulation of the cyclin pathway to control silk gland development. Taken together, it can be concluded from our results that Bmsage is involved in the determination of cell number in silk glands. Our results help clarify the process of cell number determination in silk gland and identify a potential target for silkworm breeding.

Discovering genes responsible for silk synthesis in Bombyx mori by piggyBac-based random insertional mutagenesis

Silkworm mutants are valuable resources for both transgenic breeding and gene discovery. PiggyBac-based random insertional mutagenesis has been widely used in gene functional studies. In order to discover genes involved in silk synthesis, a piggyBac-based random insertional library was constructed using Bombyx mori, and the mutants with abnormal cocoon were particularly screened. By this means, a "thin cocoon" mutant was identified. This mutant revealed thinner cocoon shell and shorter posterior silk gland (PSG) compared with the wild type. The messenger RNA (mRNA) levels of all the three fibroin genes, including Fib-H, Fib-L and P25, were significantly down-regulated in the PSG of mutants. Four piggyBac insertion sites were identified in Aquaporin (AQP), Longitudinals lacking protein-like (Lola), Glutamyl aminopeptidase-like (GluAP) and Loc101744460. The mRNA levels of all the four genes were significantly altered in the silk gland of mutants. In particular, the mRNA amount of AQP, a gene responsible for the regulation of osmotic pressure, decreased dramatically immediately prior to the spinning stage in the anterior silk gland of mutants. The identification of the genes disrupted in the "thin cocoon" mutant in this study provided useful information for understanding silk production and transgenic breeding of silkworms in the future.

Synergism of open chromatin regions involved in regulating genes in Bombyx mori

The dynamic variability of transcription factors (TFs) and their binding sites makes it challenging to conduct genome-wide transcription regulation research. The silkworm Bombyx mori, which produces silk, is one of the most valuable model insects in the order Lepidoptera. The "opening" and "closing" of chromatin in different silk yield strains is associated with changes in silk production, making this insect a good model for studying the transcriptional regulation of genes. However, few studies have examined the open chromatin regions (OCRs) of silkworms, and studying OCR synergism and their function in silk production remains challenging. Here, we performed formaldehyde-assisted isolation of regulatory elements (FAIRE) to isolate OCRs from the silk glands of fifth-instar larvae of the DaZao and D872 strains. In total, 128,908 high confidence OCRs were identified and approximately 80% of OCRs were located in non-coding regions. OCRs upregulated adjacent genes and showed signal-dependent vulnerability to single-nucleotide polymorphisms. Mid- and low-signal OCRs were more likely to have single-nucleotide polymorphisms (SNP). Further, OCRs interacted with each other within a distance of 5 kb. We named the OCR interaction complex as the "cluster of related regions" (COREs). The functions of the CORE and its harbored OCRs showed some differences. Additionally, COREs enriched many silk protein synthesis-associated genes, some of which were upregulated. This study identified numerous high confidence regulation sites and synergistic regulatory modes of OCRs that affect adjacent genes. These results provide insight into silkworm transcriptional regulation and improve our understanding of cis-element cooperation.

Identification of Genes that Control Silk Yield by RNA Sequencing Analysis of Silkworm (Bombyx mori) Strains of Variable Silk Yield

Silk is an important natural fiber of high economic value, and thus genetic study of the silkworm is a major area of research. Transcriptome analysis can provide guidance for genetic studies of silk yield traits. In this study, we performed a transcriptome comparison using multiple silkworms with different silk yields. A total of 22 common differentially expressed genes (DEGs) were identified in multiple strains and were mainly involved in metabolic pathways. Among these, seven significant common DEGs were verified by quantitative reverse transcription polymerase chain reaction, and the results coincided with the findings generated by RNA sequencing. Association analysis showed that BGIBMGA003330 and BGIBMGA005780 are significantly associated with cocoon shell weight and encode uridine nucleosidase and small heat shock protein, respectively. Functional annotation of these genes suggest that these play a role in silkworm silk gland development or silk protein synthesis. In addition, we performed principal component analysis (PCA) in combination with wild silkworm analysis, which indicates that modern breeding has a stronger selection effect on silk yield traits than domestication, and imply that silkworm breeding induces aggregation of genes related to silk yield.

Titanium nanoparticles influence the Akt/Tor signal pathway in the silkworm, Bombyx mori, silk gland

Various nanoparticles, such as silver nanoparticles (AgNPs) and titanium nanoparticles (TiO₂ NPs) are increasingly used in industrial processes. Because they are released into the environment, research into their influence on the biosphere is necessary. Among its other effects, dietary TiO₂ NPs promotes silk protein synthesis in silkworms, which prompted our hypothesis that TiO₂ NPs influence protein kinase B (Akt)/Target of rapamycin (Tor) signaling pathway (Akt/Tor) signaling in their silk glands. The Akt/Tor signaling pathway is a principle connector integrating cellular reactions to growth factors, metabolites, nutrients, protein synthesis, and stress. We tested our hypothesis by determining the influence of dietary TiO₂ NPs (for 72 h) and, separately, of two Akt/Tor pathway inhibitors (LY294002 and rapamycin) on expression of Akt/Tor signaling pathway genes and proteins in the silk glands. TiO₂ NPs treatments led to increased accumulation of mRNAs for Akt, Tor1 and Tor2 by 1.6-, 12.1-, and 4.8-fold. Dietary inhibitors led to 2.6- to 4-fold increases in mRNAs encoding Akt and substantial decreases in mRNAs encoding Tor1 and Tor2. Western blot analysis showed that dietary TiO₂ NPs increased the phosphorylation of Akt and its downstream proteins. LY294002 treatments led to inhibition of Akt phosphorylation and its downstream proteins and rapamycin treatments similarly inhibited the phosphorylation of Tor-linked downstream proteins. These findings support our hypothesis that TiO₂ NPs influence Akt/Tor signaling in silk glands. The significance of this work is identification of specific sites of TiO₂ NPs actions.

Transgenic Silkworm-Based Silk Gland Bioreactor for Large Scale Production of Bioactive Human Platelet-Derived Growth Factor (PDGF-BB) in Silk Cocoons

Human platelet derived growth factor (PDGF) is a major therapeutic protein with great demand in the clinical setting; however, its rate of supply is far from meeting needs. Here, we provide an effective strategy to produce PDGF-BB in large quantities using a transgenic silkworm. The codon-optimized PDGF-B gene regulated by the highly efficient sericin-1 expression system was integrated into the genome of a silkworm. The high transcriptional expression of the PDGF-BB gene in the transgenic silkworm competitively inhibited the transcription expression of the endogenous sericin-1 gene which caused a significant 37.5% decline. The PDGF-BB synthesized in the middle silk gland (MSG) of transgenic silkworms could form a homodimer through intermolecular disulfide bonds, which is then secreted into sericin lumen and finally, distributed in the sericin layer of the cocoon. In this study, a protein quantity of approximately 0.33 mg/g was found in the cocoon. Following a purification process, approximately 150.7 μg of recombinant PDGF-BB with a purity of 82% was purified from 1 g of cocoons. Furthermore, the bioactivity assays showed that the purified recombinant PDGF-BB was able to promote the growth, proliferation and migration of NIH/3T3 cells significantly. These results suggest that the silk gland bioreactor can produce active recombinant PDGF-BB as an efficient mitogen and wound healing agent.

Identification and comparison of long non-coding RNAs in the silk gland between domestic and wild silkworms

Under long-term artificial selection, the domestic silkworm (Bombyx mori) has increased its silk yield tremendously in comparison with its wild progenitor, Bombyx mandarina. However, the molecular mechanism of silk yield increase is still unknown. Comparative analysis of long non-coding RNAs (lncRNAs) may provide some insights into understanding this phenotypic variation. In this study, using RNA sequencing technology data of silk gland in domestic and wild silkworms, we identified 599 lncRNAs in the silk gland of the silkworm. Compared with protein-coding genes, the silk gland lncRNA genes tend to have fewer exon numbers, shorter transcript length and lower GC-content. Moreover, we found that three lncRNA genes are significantly and differentially expressed between domestic and wild silkworms. The potential targets of two differentially expressed lncRNAs (DELs) (dw4sg_0040 and dw4sg_0483) and the expression-correlated genes with the two DELs are mainly enriched in the related processes of silk protein translation. This implies that these DELs may affect the phenotypic variation in silk yield between the domestic and wild silkworms through the post-transcriptional regulation of silk protein.

Apoptosis of posterior silk gland of Bombyx mori during spinning period and the role of PI3K/Akt pathway

Bombyx mori is an economic insect of the Lepidoptera. Its posterior silk gland (PSG) is an important organ for fibroin synthesis. In order to study the occurrence of apoptosis in PSG and the role of PI3K/Akt signaling pathway during spinning period, changes in morphology of silk gland, expressions of fibroin components Fib-H, Fib-L and P25 and Akt, TOR2, P70S6K and S6 in PI3K/Akt pathway, expressions of apoptosis related genes caspase-3, caspase-9 and activity of caspase-3 were explored. The results showed that the morphology of silk gland dramatically degenerated; transcription of Fib-H, Fib-L, and P25 gradually declined with time; and Fib-L protein level reduced by 0.6-fold at 72 h. Moreover, the transcription levels of Akt, TOR2, P70S6K, and S6 also decreased by 0.3-, 0.8-, 0.7-, and 0.1-fold, respectively, indicating that the downregulation of PI3K/Akt signaling pathway could lead to reduction in fibroin synthesis. In addition, the transcription levels of caspase-3 and caspase-9 increased by 1.3- and 3.6-fold, respectively, and the enzyme activity of caspase-3 grew at a maximum of 1.6-fold. The results showed the occurrence of apoptosis in PSG during spinning period. In conclusion, the present study indicated that both the decline in fibroin components and the increase in apoptosis-related genes were regulated by PI3K/Akt signaling pathway during spinning period, which shed new light on the functions of PI3K/Akt signaling pathway.

Improved strength of silk fibers in Bombyx mori trimolters induced by an anti-juvenile hormone compound

BACKGROUND

Bombyx mori silk fibers with thin diameters have advantages of lightness and crease-resistance. Many studies have used anti-juvenile hormones to induce trimolters in order to generate thin silk; however, there has been comparatively little analysis of the morphology, structure and mechanical properties of trimolter silk.

METHODS

This study induced two kinds of trimolters by appling topically anti-juvenile hormones and obtained thin diameter silk. Scanning electron microscope (SEM), FTIR analysis, tensile mechanical testing, chitin staining were used to reveal that the morphology, conformation and mechanical property of the trimolter silk.

RESULTS

Cocoon of trimolters were highly densely packed by thinner fibers and thus had small apertures. We found that the conformation of trimolter silk fibroin changed and formed more β-sheet structures. In addition, analysis of mechanical parameters yielded a higher Young's modulus and strength in trimolter silk than in the control. By chitin staining of silk gland, we postulated that the mechanical properties of trimolters' silk was enhanced greatly during to the structural changes of silk gland.

CONCLUSION

We induced trimolters by anti-juvenile hormones and the resulting cocoons were more closely packed and had smaller silk fiber diameters. We found that the conformation of trimolters silk fibroin had a higher content of β-sheet structures and better mechanical properties.

GENERAL SIGNIFICANCE

Our study revealed the structures and mechanical properties of trimolter silk, and provided a valuable reference to improve silk quality by influencing molting in silkworms.

Analysis of the pressure requirements for silk spinning reveals a pultrusion dominated process

Silks are remarkable materials with desirable mechanical properties, yet the fine details of natural production remain elusive and subsequently inaccessible to biomimetic strategies. Improved knowledge of the natural processes could therefore unlock development of a host of bio inspired fibre spinning systems. Here, we use the Chinese silkworm Bombyx mori to review the pressure requirements for natural spinning and discuss the limits of a biological extrusion domain. This provides a target for finite element analysis of the flow of silk proteins, with the aim of bringing the simulated and natural domains into closer alignment. Supported by two parallel routes of experimental validation, our results indicate that natural spinning is achieved, not by extruding the feedstock, but by the pulling of nascent silk fibres. This helps unravel the oft-debated question of whether silk is pushed or pulled from the animal, and provides impetus to the development of pultrusion-based biomimetic spinning devices.The natural production of silks remains elusive and subsequently inaccessible to biomimetic strategies. Here the authors show that silks cannot be spun by pushing alone, and that natural spinning is dominated by pultrusion, which provides design guidelines for future biomimetic spinning systems.

Antheraea pernyi (Lepidoptera: Saturniidae) and Its Importance in Sericulture, Food Consumption, and Traditional Chinese Medicine

Sericulture was developed in China in ancient times. Antheraea pernyi Guérin-Méneville was domesticated at least 2,000 yr ago, and Chinese farmers developed artificial rearing of A. pernyi before the 17th century. Today, >60,000 tons of cocoons are produced in China each year, which accounts for 90% of the world production. Despite the widespread utilization of A. pernyi in China and a long history of domestic research, the knowledge of A. pernyi outside China is limited. Therefore, we have in this paper summarized the production, usage, and breeding of A. pernyi. The foremost usage of A. pernyi is as silk producers; however, about 55-70% is used for other purposes. In this paper, we give examples of how the different developmental stages are used as a food source for human consumption and in traditional Chinese medicine, both directly in different preparations and also as a nutrient source for rearing medicinal fungi.

Increasing the yield of middle silk gland expression system through transgenic knock-down of endogenous sericin-1

Various genetically modified bioreactor systems have been developed to meet the increasing demands of recombinant proteins. Silk gland of Bombyx mori holds great potential to be a cost-effective bioreactor for commercial-scale production of recombinant proteins. However, the actual yields of proteins obtained from the current silk gland expression systems are too low for the proteins to be dissolved and purified in a large scale. Here, we proposed a strategy that reducing endogenous sericin proteins would increase the expression yield of foreign proteins. Using transgenic RNA interference, we successfully reduced the expression of BmSer1 to 50%. A total 26 transgenic lines expressing Discosoma sp. red fluorescent protein (DsRed) in the middle silk gland (MSG) under the control of BmSer1 promoter were established to analyze the expression of recombinant. qRT-PCR and western blotting showed that in BmSer1 knock-down lines, the expression of DsRed had significantly increased both at mRNA and protein levels. We did an additional analysis of DsRed/BmSer1 distribution in cocoon and effect of DsRed protein accumulation on the silk fiber formation process. This study describes not only a novel method to enhance recombinant protein expression in MSG bioreactor, but also a strategy to optimize other bioreactor systems.

YorkieCA overexpression in the posterior silk gland improves silk yield in Bombyx mori

The traditional hybrid breeding techniques can no longer meet the increasing demands for silk production by the silkworm, Bombyx mori, and further improvement of the silk yield will depend on modern molecular breeding techniques. Here, we report improved silk yield in transgenic silkworms overexpressing the oncogene Yorkie^CA specifically in the posterior silk gland (PSG). The Yorkie^CA cDNA was ligated downstream of the hr3 enhancer and the fibroin L-chain (Fil) promoter, then inserted into a piggyBac vector for transgene. Overexpression of Yorkie^CA in the PSG significantly increased the weight of the PSG, and also increased the weight of the cocoon, larval body, and pupal body to decreasing degrees. Overexpression of Yorkie^CA up-regulated the Yorkie target genes resulting in increased cell size, endomitosis, the number of protein synthesis organelles, the expression of fibroin genes in the PSG, and eventually silk yield. Additionally, as we reported previously using the binary GAL4/UAS system, transgenic silkworms overexpressing Ras1^CA with the hr3 enhancer and the Fil promoter also showed improved silk yield. Unfortunately, the hybrid progeny of Yorkie^CA-overexpressing silkworms and Ras1^CA-overexpressing silkworms did not show overlapping improved silk yield due to the failure to increase expression of both Yorkie and Ras1.

Functionalized silk assembled from a recombinant spider silk fusion protein (Z-4RepCT) produced in the methylotrophic yeast Pichia pastoris

Functional biological materials are a growing research area with potential applicability in medicine and biotechnology. Using genetic engineering, the possibility to introduce additional functions into spider silk-based materials has been realized. Recently, a recombinant spider silk fusion protein, Z-4RepCT, was produced intracellularly in Escherichia coli and could after purification self-assemble into silk-like fibers with ability to bind antibodies via the IgG-binding Z domain. In this study, the use of the methylotrophic yeast Pichia pastoris for production of Z-4RepCT has been investigated. Temperature, pH and production time were influencing the amount of soluble Z-4RepCT retrieved from the extracellular fraction. Purification of secreted Z-4RepCT resulted in a mixture of full-length and degraded silk proteins that failed to self-assemble into fibers. A position in the C-terminal domain of 4RepCT was identified as being subjected to proteolytic cleavage by proteases in the Pichia culture supernatant. Moreover, the C-terminal domain was subjected to glycosylation during production in P. pastoris. These observed alterations of the CT domain are suggested to contribute to the failure in fiber assembly. As alternative approach, Z-4RepCT retrieved from the intracellular fraction, which was less degraded, was used and shown to retain ability to assemble into silk-like fibers after enzymatic deglycosylation.

Comparative transcriptome analysis of Bombyx mori spinnerets and Filippi's glands suggests their role in silk fiber formation

The spinneret is located at the end of silk glands in the silkworm, Bombyx mori. The Filippi's gland (FG), which communicates with the silk gland, is considered an accessory to the latter. Although these two organs have been known for centuries, only their morphology has been studied. Their gene expression profiles and physiological roles are still unknown. Aided by next-generation sequencing, we profiled more than 11000 transcripts from the spinneret and FG of silkworm larvae on day 3 of the fifth instar (L5D3) and wandering stage (W1) in this study. A total of 59 ion-transporting protein genes and 106 cuticle protein genes were identified in the spinneret. To analyze the dynamic changes in the expression of spinneret genes, differential expression analysis was performed, and 1452 differentially expressed genes (DEGs) were identified in spinneret tissue harvested on L5D3 and W1 of the silkworm larvae. Gene Ontology (GO) enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment of the DEGs revealed that the spinneret had active ion-transporting, chitin binding, and energy metabolism processes at W1. Based on these data, we hypothesized that the role of the spinneret is to provide a favorable physiological environment for the silk fiber formation. Furthermore, differential expression analysis and GO enrichment of the DEGs in the FG suggested a possible role of this gland in transporting small solutes such as ions, sugars and amino acids to the silk gland. Our findings pave a way for further functional explanation of the spinneret and FG.

[Identification and expression patterns of anterior silk gland specific cuticle protein Bm11721 in the silkworm (Bombyx mori)]

The silk gland of silkworm is the organ of silk protein synthesis and secretion. According to the morphological and functional differences, silk gland can be divided into anterior silk gland (ASG), middle silk gland (MSG) and posterior silk gland (PSG). ASG is the place for silk proteins conformation changes although it cannot synthetize silk proteins. ASG has narrow luminal structures and rigid wall which consists of chitin and cuticle proteins so that it can provide the shearing force which plays an important role in the silk protein conformation changes. The objective of this study is to identify the new chitin binding proteins in ASG of silkworm (Bombyx mori), and to analyze their expression patterns in different tissues. We identified a cuticle protein with chitin binding domain Bml1721 (GenBank Accession No. NM-001173285.1) by chitin affinity chromatography column. We also expressed the recombinant protein as inclusion body using the prokaryotic expression system, and then successfully purified the recombinant protein by nickel affinity chromatography column to generate the polyclonal antibodies. The expression patterns analysis in various tissues showed that both in transcriptional and protein levels Bm11721 was specifically expressed in ASG. Furthermore, the expression level of Bm 11721 protein was unchanged during the 5th instar. Immunofluorescence analysis revealed that Bm1 1721 was located in the ASG inner membrane. It is proposed that Bm11721 is a component of inner membrane and probably provides the shearing force for conformational changes.

Mechanical behaviour and formation process of silkworm silk gut

High performance silk fibers were produced directly from the silk glands of silkworms (Bombyx mori) following an alternative route to natural spinning. This route is based on a traditional procedure that consists of soaking the silk glands in a vinegar solution and stretching them by hand leading to the so called silkworm guts. Here we present, to the authors' best knowledge, the first comprehensive study on the formation, properties and microstructure of silkworm gut fibers. Comparison of the tensile properties and microstructural organization of the silkworm guts with those of naturally spun fibers allows gain of a deeper insight into the mechanisms that lead to the formation of the fiber, as well as the relationship between the microstructure and properties of these materials. In this regard, it is proved that an acidic environment and subsequent application of tensile stress in the range of 1000 kPa are sufficient conditions for the formation of a silk fiber.

Carbonic anhydrase generates a pH gradient in Bombyx mori silk glands

Silk is a protein of interest to both biological and industrial sciences. The silkworm, Bombyx mori, forms this protein into strong threads starting from soluble silk proteins using a number of biochemical and physical cues to allow the transition from liquid to fibrous silk. A pH gradient has been measured along the gland, but the methodology employed was not able to precisely determine the pH at specific regions of interest in the silk gland. Furthermore, the physiological mechanisms responsible for the generation of this pH gradient are unknown. In this study, concentric ion selective microelectrodes were used to determine the luminal pH of B. mori silk glands. A gradient from pH 8.2 to 7.2 was measured in the posterior silk gland, with a pH 7 throughout the middle silk gland, and a gradient from pH 6.8 to 6.2 in the beginning of the anterior silk gland where silk processing into fibers occurs. The small diameter of the most anterior region of the anterior silk gland prevented microelectrode access in this region. Using a histochemical method, the presence of active carbonic anhydrase was identified in the funnel and anterior silk gland of fifth instar larvae. The observed pH gradient collapsed upon addition of the carbonic anhydrase inhibitor methazolamide, confirming an essential role for this enzyme in pH regulation in the B. mori silk gland. Plastic embedding of whole silk glands allowed clear visualization of the morphology, including the identification of four distinct epithelial cell types in the gland and allowed correlations between silk gland morphology and silk stages of assembly related to the pH gradient. B. mori silk glands have four different epithelial cell types, one of which produces carbonic anhydrase. Carbonic anhydrase is necessary for the mechanism that generates an intraluminal pH gradient, which likely regulates the assembly of silk proteins and then the formation of fibers from soluble silk proteins. These new insights into native silk formation may lead to a more efficient production of artificial or regenerated silkworm silk fibers.

Molecular mechanisms of silk gland damage caused by phoxim exposure and protection of phoxim-induced damage by cerium chloride in Bombyx mori

It is known that exposure to organophosphorus pesticides (OP) including phoxim can produce oxidative stress, neurotoxicity, and greatly attenuate cocooning rate in the silkworm, Bombyx mori. Cerium treatment has been demonstrated to relieve phoxim-induced toxicity in B. mori; however, very little is known about the molecular mechanisms of silk gland injury due to OP exposure and protection of gland damage due to cerium pretreatment. The aim of this study was to evaluate silk gland damage and its molecular mechanisms in phoxim-induced silkworm toxicity and the protective mechanisms of cerium following exposure to phoxim. The results showed that phoxim exposure resulted in severe gland damage, reductions in protein synthesis and the cocooning rate of silkworms. Cerium (Ce) attenuated gland damage caused by phoxim, promoted protein synthesis, increased the antioxidant capacity of the gland and increased the cocooning rate of B. mori. Furthermore, digital gene expression data suggested that phoxim exposure led to significant up-regulation of 714 genes and down-regulation of 120 genes. Of these genes, 122 were related to protein metabolism, specifically, the down-regulated Ser2, Ser3, Fib-L, P25, and CYP450. Ce pretreatment resulted in up-regulation of 162 genes, and down-regulation of 141 genes, importantly, Ser2, Ser3, Fib-L, P25, and CYP333B8 were up-regulated. Treatment with CeCl3 + phoxim resulted in higher levels of Fib-L, P25, Ser2, Ser3, CAT, TPx, and CYP333B8 expression in the silk gland of silkworms. These findings indicated that Ce increased cocooning rate via the promotion of silk protein synthesis-related gene expression in the gland under phoxim-induced toxicity. These findings may expand the application of rare earths in sericulture.

Nanoparticulate anatase TiO2 (TiO2 NPs) upregulates the expression of silkworm (Bombyx mori) neuropeptide receptor and promotes silkworm feeding, growth, and silking

Bombyx mori orphan G protein-coupled receptor, BNGR-A4, is the specific receptor of B. mori neuropeptide F (BmNPFR, neuropeptide F designated NPF). BmNPFR binds specifically and efficiently to B. mori neuropeptides BmNPF1a and BmNPF1b, which activates the ERK1/2 signaling pathway to regulate B. mori food intake and growth. Titanium dioxide nanoparticles (TiO2 NPs) can promote B. mori growth. However, whether the mechanisms of TiO2 NPs' effects are correlated with BmNPFR remains unknown. In this study, the effects of TiO2 NPs (5mg/L) feeding and BmNPFR-dsRNA injection on B. mori food intake and growth were investigated; after TiO2 NPs treatments, B. mori food intake, body weight, and cocoon shell weight were 5.82%, 4.64%, and 9.30% higher, respectively, than those of controls. The food intake, body weight, and cocoon shell weight of the BmNPFR-dsRNA injection group were reduced by 8.05%, 6.28%, and 6.98%, respectively, compared to the control. After TiO2 NPs treatment for 72h, the transcriptional levels of BmNPFR, BmNPF1a, and BmNPF1b in the midgut were 1.58, 1.43, and 1.34-folds, respectively, of those of the control, but 1.99, 2.26, and 2.19-folds, respectively, of the BmNPFR-dsRNA injection group; the phosphorylation level of MAPK was 24.03% higher than the control, while the phosphorylation level of BmNPFR-dsRNA injection group was 71.00% of control. The results indicated that TiO2 NPs affect B. mori feeding and growth through increasing the expression of BmNPFR. This study helps clarify the roles of BmNPF/BmNPFR system in TiO2 NPs' effects on B. mori feeding, growth, and development.

Predictive modelling-based design and experiments for synthesis and spinning of bioinspired silk fibres

Scalable computational modelling tools are required to guide the rational design of complex hierarchical materials with predictable functions. Here, we utilize mesoscopic modelling, integrated with genetic block copolymer synthesis and bioinspired spinning process, to demonstrate de novo materials design that incorporates chemistry, processing and material characterization. We find that intermediate hydrophobic/hydrophilic block ratios observed in natural spider silks and longer chain lengths lead to outstanding silk fibre formation. This design by nature is based on the optimal combination of protein solubility, self-assembled aggregate size and polymer network topology. The original homogeneous network structure becomes heterogeneous after spinning, enhancing the anisotropic network connectivity along the shear flow direction. Extending beyond the classical polymer theory, with insights from the percolation network model, we illustrate the direct proportionality between network conductance and fibre Young's modulus. This integrated approach provides a general path towards de novo functional network materials with enhanced mechanical properties and beyond (optical, electrical or thermal) as we have experimentally verified.

The spinning apparatus of webspinners--functional-morphology, morphometrics and spinning behaviour

Webspinners (Insecta: Embioptera) have a distinctly unique behaviour with related morphological characteristics. Producing silk with the basitarsomeres of their forelegs plays a crucial role in the lives of these insects--providing shelter and protection. The correlation between body size, morphology and morphometrics of the spinning apparatus and the spinning behaviour of Embioptera was investigated for seven species using state-of-the-art methodology for behavioural as well as for morphological approaches. Independent contrast analysis revealed correlations between morphometric characters and body size. Larger webspinners in this study have glands with greater reservoir volume, but in proportionally smaller tarsi relative to body size than in the smaller species. Furthermore, we present a detailed description and review of the spinning apparatus in Embioptera in comparison to other arthropods and substantiate the possible homology of the embiopteran silk glands to class III dermal silk glands of insects.

GC/MS-based metabolomic studies reveal key roles of glycine in regulating silk synthesis in silkworm, Bombyx mori

Metabolic profiling of silkworm, especially the factors that affect silk synthesis at the metabolic level, is little known. Herein, metabolomic method based on gas chromatography-mass spectrometry was applied to identify key metabolic changes in silk synthesis deficient silkworms. Forty-six differential metabolites were identified in Nd group with the defect of silk synthesis. Significant changes in the levels of glycine and uric acid (up-regulation), carbohydrates and free fatty acids (down-regulation) were observed. The further metabolomics of silk synthesis deficient silkworms by decreasing silk proteins synthesis using knocking out fibroin heavy chain gene or extirpating silk glands operation showed that the changes of the metabolites were almost consistent with those of the Nd group. Furthermore, the increased silk yields by supplying more glycine or its related metabolite confirmed that glycine is a key metabolite to regulate silk synthesis. These findings provide important insights into the regulation between metabolic profiling and silk synthesis.

Ca2+ and endoplasmic reticulum Ca2+-ATPase regulate the formation of silk fibers with favorable mechanical properties

Calcium ions (Ca(2+)) are crucial for the conformational transition of silk fibroin in vitro, and silk fibroin conformations correlate with the mechanical properties of silk fibers. To investigate the relationship between Ca(2+) and mechanical properties of silk fibers, CaCl2 was injected into silkworms (Bombyx mori). Fourier-transform infrared spectroscopy (FTIR) analysis and mechanical testing revealed that injection of CaCl2 solution (7.5mg/g body weight) significantly increased the levels of α-helix and random coil structures of silk proteins. In addition, extension of silk fibers increased after CaCl2 injection. In mammals, sarcoplasmic reticulum Ca(2+)-ATPase in muscle and endoplasmic reticulum Ca(2+)-ATPase in other tissues (together denoted by SERCA) are responsible for calcium balance. Therefore, we analyzed the expression pattern of silkworm SERCA (BmSERCA) in silk glands and found that BmSERCA was abundant in the anterior silk gland (ASG). After injection of thapsigargin (TG) to block SERCA activity, silkworms showed a silk-spinning deficiency and their cocoons had higher calcium content compared to that of controls. Moreover, FTIR analysis revealed that the levels of α-helix and β-sheet structures increased in silk fibers from TG-injected silkworms compared to controls. The results provide evidence that BmSERCA has a key function in calcium transportation in ASG that is related to maintaining a suitable ionic environment. This ionic environment with a proper Ca(2+) concentration is crucial for the formation of silk fibers with favorable mechanical performances.

A juvenile hormone transcription factor Bmdimm-fibroin H chain pathway is involved in the synthesis of silk protein in silkworm, Bombyx mori

The genes responsible for silk biosynthesis are switched on and off at particular times in the silk glands of Bombyx mori. This switch appears to be under the control of endogenous and exogenous hormones. However, the molecular mechanisms by which silk protein synthesis is regulated by the juvenile hormone (JH) are largely unknown. Here, we report a basic helix-loop-helix transcription factor, Bmdimm, its silk gland-specific expression, and its direct involvement in the regulation of fibroin H-chain (fib-H) by binding to an E-box (CAAATG) element of the fib-H gene promoter. Far-Western blots, enzyme-linked immunosorbent assays, and co-immunoprecipitation assays revealed that Bmdimm protein interacted with another basic helix-loop-helix transcription factor, Bmsage. Immunostaining revealed that Bmdimm and Bmsage proteins are co-localized in nuclei. Bmdimm expression was induced in larval silk glands in vivo, in silk glands cultured in vitro, and in B. mori cell lines after treatment with a JH analog. The JH effect on Bmdimm was mediated by the JH-Met-Kr-h1 signaling pathway, and Bmdimm expression did not respond to JH by RNA interference with double-stranded BmKr-h1 RNA. These data suggest that the JH regulatory pathway, the transcription factor Bmdimm, and the targeted fib-H gene contribute to the synthesis of fibroin H-chain protein in B. mori.

Film Formation and Structural Characterization of Silk of the Hornet Vespa simillima xanthoptera Cameron

We extracted silk produced by the larva of the hornet Vespa simillima xanthoptera Cameron from its nest. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis of the extracted hornet silk showed four major components with molecular weights between 35 and 60 kDa. The main amino acid components of the hornet silk protein were Ala (33.5%), Ser (16.9%), Asp (8.5%) and Glu (8.1%). The hornet silk could be dissolved in hexafluoroisopropyl alcohol (HFIP) at 25 °C without incurring molecular degradation. A transparent film of hornet silk was obtained readily by the formation of a cast upon drying of the hornet silk in the HFIP solution. Residual HFIP solvent was removed from the film by extraction with pure water. Solid-state 13C NMR and FT-IR measurements revealed that the secondary structures of hornet silk proteins in the native state consisted of coexisting α-helix and β-sheet conformations. The β-sheet to α-helix ratio, which was changed by processing, was mainly responsible for the silk’s thermostability.

Cross-linking in the silks of bees, ants and hornets

Silk production is integral to the construction of nests or cocoons for many Aculeata, stinging Hymenopterans such as ants, bees and wasps. Here we report the sequences of new aculeate silk proteins and compare cross-linking among nine native silks from three bee species (Apis mellifera, Bombus terrestris and Megachile rotundata), three ant species (Myrmecia forficata, Oecophylla smaragdina and Harpegnathos saltator) and three hornets (Vespa analis, Vespa simillima and Vespa mandarinia). The well studied silks of spiders and silkworms are comprised of large proteins that are cross-linked and stabilized predominantly by intra and intermolecular beta sheet structure. In contrast, the aculeate silks are comprised of relatively small proteins that contain central coiled coil domains and comparatively reduced amounts of beta sheet structure. The hornet silks, which have the most beta sheet structure and the greatest amount of amino acid sequence outside the coiled-coil domains, dissolve in concentrated LiBr solution and appear to be stabilized predominantly by beta sheet structure like the classic silks. In contrast, the ant and bee silks, which have less beta sheet and less sequence outside the coiled-coil domains, could not be dissolved in LiBr and appear to be predominantly stabilized by covalent cross-linking. The iso-peptide cross-linker, ε-(γ-glutamyl)-lysine that is produced by transglutaminase enzymes, was demonstrated to be present in all silks by mass spectrometry, but at greater levels in silks of ants and bees. The bee silks and ant cocoons, but not the Oecophylla nest silks, appeared to be further stabilized by tanning reactions.

Transglutamination allows production and characterization of native-sized ELPylated spider silk proteins from transgenic plants

In the last two decades it was shown that plants have a great potential for production of specific heterologous proteins. But high cost and inefficient downstream processing are a main technical bottleneck for the broader use of plant-based production technology especially for protein-based products, for technical use as fibres or biodegradable plastics and also for medical applications. High-performance fibres from recombinant spider silks are, therefore, a prominent example. Spiders developed rather different silk materials that are based on proteins. These spider silks show excellent properties in terms of elasticity and toughness. Natural spider silk proteins have a very high molecular weight, and it is precisely this property which is thought to give them their strength. Transgenic plants were generated to produce ELPylated recombinant spider silk derivatives. These fusion proteins were purified by Inverse Transition Cycling (ITC) and enzymatically multimerized with transglutaminase in vitro. Layers produced by casting monomers and multimers were characterized using atomic force microscopy (AFM) and AFM-based nanoindentation. The layered multimers formed by mixing lysine- and glutamine-tagged monomers were associated with the highest elastic penetration modulus.

Spermidine enhances the silk production by mulberry silkworm

Polyamines are ubiquitous low molecular weight polycationic aliphatic amines involved in diverse cellular processes. Spermidine (Spd), a polyamine, has been proved to be crucial for cell survival in various organisms. Our study reports the effect of Spd on the growth of Bombyx mori. Silkworms showed improved silk gland weight and economic parameters in the fifth instar larval stage when treated with different concentrations of Spd, in the range of 25-75 µM. The worms treated with Spd produced 31% more silk when compared with the control worms. Altogether, this study establishes that Spd-treated leaves can be fed into the larvae for better silk production.

Titanium dioxide nanoparticles relieve silk gland damage and increase cocooning of Bombyx mori under phoxim-induced toxicity

Organophosphate pesticides are applied widely in the world for agricultural purposes, and their exposures often resulted in non-cocooning of Bombyx mori in China. TiO2 nanoparticles have been demonstrated to increase pesticide resistance of Bombyx mori. While the toxicity of phoxim is well-documented, very limited information exists on the mechanisms of TiO2 nanoparticles improving the cocooning function of Bombyx mori following exposure to phoxim. The present study was, therefore, undertaken to determine whether TiO2 nanoparticles attenuate silk gland injury and elevate cocooning of B. mori following exposure to phoxim. The findings suggested that phoxim exposure resulted in severe damages of the silk gland structure and significantly decreased the cocooning in the silk gland of Bombyx mori. Furthermore, phoxim exposure significantly resulted in reductions of total protein concentrations and suppressed expressions of silk protein synthesis-related genes, including Fib-L, Fib-H, P25, Ser-2, and Ser-3, in the silk gland. TiO2 nanoparticle pretreatment, however, could significantly relieve silk gland injury of Bombyx mori. Importantly, TiO2 nanoparticles could remarkably elevate cocooning and total protein contents and promote expressions of Fib-L, Fib-H, P25, Ser-2, and Ser-3 in the silk gland following exposure to phoxim.

The effect of bovine milk on the growth of Bombyx mori

Bombyx mori L. (Lepidoptera: Bombycidae) is a well-studied Lepidopteran model system because of its morphology, life cycle, and economic importance. Many scientists have placed importance on enhancing the economic traits of B. mori because it's larvae, silkworms, are vital in the production of silk. In this study, the effect of bovine milk on B. mori growth was tested. Bovine milk contains several components that aid in healthy growth. The treatment was given to fifth instar B. mori larvae because the fifth instar period is when B. mori eats voraciously and shows maximum growth among all its larval stages. The larvae were treated with fresh mulberry, Morus L. (Rosales: Moraceae), leaves and mulberry leaves dipped in milk from the first day of the fifth instar. Treatments were given on alternate days, and the silkworms were weighed every day to determine whether milk had any role in enhancing the weight of the larvae. Cocoon weights were measured, as the weight indicates the approximate amount of silk that can be reeled. The results showed that larvae gained 82.5% more weight by the end of fifth instar larval when fed with mulberry leaves dipped in milk than when fed with fresh mulberry leaves without milk. The larvae fed with milk-treated leaves gained 310% weight from day 1 to day 7 of the fifth instar, while the larvae fed with fresh leaves gained 153% weight in the same timespan. In addition, cocoon weight increased by 8% when milk was added compared to when it was not. These results suggest that B. mori larvae can be fed mulberry leaves treated with bovine milk for better growth rate and increased silk production.

How did the spider cross the river? Behavioral adaptations for river-bridging webs in Caerostris darwini (Araneae: Araneidae)

BACKGROUND

Interspecific coevolution is well described, but we know significantly less about how multiple traits coevolve within a species, particularly between behavioral traits and biomechanical properties of animals' "extended phenotypes". In orb weaving spiders, coevolution of spider behavior with ecological and physical traits of their webs is expected. Darwin's bark spider (Caerostris darwini) bridges large water bodies, building the largest known orb webs utilizing the toughest known silk. Here, we examine C. darwini web building behaviors to establish how bridge lines are formed over water. We also test the prediction that this spider's unique web ecology and architecture coevolved with new web building behaviors.

METHODOLOGY

We observed C. darwini in its natural habitat and filmed web building. We observed 90 web building events, and compared web building behaviors to other species of orb web spiders.

CONCLUSIONS

Caerostris darwini uses a unique set of behaviors, some unknown in other spiders, to construct its enormous webs. First, the spiders release unusually large amounts of bridging silk into the air, which is then carried downwind, across the water body, establishing bridge lines. Second, the spiders perform almost no web site exploration. Third, they construct the orb capture area below the initial bridge line. In contrast to all known orb-weavers, the web hub is therefore not part of the initial bridge line but is instead built de novo. Fourth, the orb contains two types of radial threads, with those in the upper half of the web doubled. These unique behaviors result in a giant, yet rather simplified web. Our results continue to build evidence for the coevolution of behavioral (web building), ecological (web microhabitat) and biomaterial (silk biomechanics) traits that combined allow C. darwini to occupy a unique niche among spiders.

Novel enhancer and promoter elements indispensable for the tissue-specific expression of the sericin-1 gene of the silkworm Bombyx mori

Sericins are glue proteins produced specifically in the middle silk gland (MSG) of the silkworm Bombyx mori, while the silk fiber protein, fibroin, is produced in the posterior silk gland (PSG). These silk proteins are expected to be useful biomaterials in medical technology as well as biotechnology. In this study, we analyzed promoter elements of the sericin-1 gene (ser1) in vivo by introducing reporter constructs into silk glands via gene gun technology. The region from -1602 to +47 was sufficient to induce MSG-specific expression. The 5' deletion mutants showed a three-step decrease in promoter activity with the key sequences located between -1362 and -1250, -201 and -116, and -115 and -37. We detected a tissue- and stage-specific factor complex (MSG-intermolt-specific complex: MIC) bound to the sequence elements around the -1350, -320, -180, and -70 regions. A mutation in the -70 region, which inhibits MIC-binding, diminished almost all promoter activity, while another mutation that did not inhibit MIC-binding showed no effect on promoter activity. The results suggest that the binding of MIC to the above elements is intrinsic for the spatiotemporal specificity of ser1 in vivo.

Plasticity in major ampullate silk production in relation to spider phylogeny and ecology

Spider major ampullate silk is a high-performance biomaterial that has received much attention. However, most studies ignore plasticity in silk properties. A better understanding of silk plasticity could clarify the relative importance of chemical composition versus processing of silk dope for silk properties. It could also provide insight into how control of silk properties relates to spider ecology and silk uses. We compared silk plasticity (defined as variation in the properties of silk spun by a spider under different conditions) between three spider clades in relation to their anatomy and silk biochemistry. We found that silk plasticity exists in RTA clade and orbicularian spiders, two clades that differ in their silk biochemistry. Orbiculariae seem less dependent on external spinning conditions. They probably use a valve in their spinning duct to control friction forces and speed during spinning. Our results suggest that plasticity results from different processing of the silk dope in the spinning duct. Orbicularian spiders seem to display better control of silk properties, perhaps in relation to their more complex spinning duct valve.

Ras1(CA) overexpression in the posterior silk gland improves silk yield

Sericulture has been greatly advanced by applying hybrid breeding techniques to the domesticated silkworm, Bombyx mori, but has reached a plateau during the last decades. For the first time, we report improved silk yield in a GAL4/UAS transgenic silkworm. Overexpression of the Ras1(CA) oncogene specifically in the posterior silk gland improved fibroin production and silk yield by 60%, while increasing food consumption by only 20%. Ras activation by Ras1(CA) overexpression in the posterior silk gland enhanced phosphorylation levels of Ras downstream effector proteins, up-regulated fibroin mRNA levels, increased total DNA content, and stimulated endoreplication. Moreover, Ras1 activation increased cell and nuclei sizes, enriched subcellular organelles related to protein synthesis, and stimulated ribosome biogenesis for mRNA translation. We conclude that Ras1 activation increases cell size and protein synthesis in the posterior silk gland, leading to silk yield improvement.

Tailoring plant metabolism for the production of novel polymers and platform chemicals

Genetic engineering of plants for the production of novel polymers and platform chemicals can help to alleviate the demands for limited resources and potentially provide a platform to produce valuable compounds in bulk quantities. However, the success of transgenic plants as bioreactors depends on competitive high-yield production capacities. Recent advances in enhancing the production of novel compounds in transgenic plants include multigene transformation and the direction of biosynthetic pathways to specific intracellular compartments. It now appears feasible to produce interesting proteins such as spider silk or collagen, novel carbohydrates, and biopolymers that could replace petroleum-based plastics using transgenic plants. Direct production of novel compounds in biomass crops with the aim to produce bioenergy as a coproduct provides a promising way to improve economics of transgenic plants as biofactories.