Transgenic Silkworms Research Articles

Construction of transformed, cultured silkworm cells and transgenic silkworm using the site-specific integrase system from phage φC31.

The Streptomyces bacteriophage, φC31, uses a site-specific integrase enzyme to perform efficient recombination. The recombination system uses specific sequences to integrate exogenous DNA from the phage into a host. The sequences are known as the attP site in the phage and the attB site in the host. The system can be used as a genetic manipulation tool. In this study it has been applied to the transformation of cultured BmN cells and the construction of transgenic Bombyx mori individuals. A plasmid, pSK-attB/Pie1-EGFP/Zeo-PASV40, containing a cassette designed to express a egfp-zeocin fusion gene, was co-transfected into cultured BmN cells with a helper plasmid, pSK-Pie1/NLS-Int/NSL. Expression of the egfp-zeocin fusion gene was driven by an ie-1 promoter, downstream of a φC31 attB site. The helper plasmid encoded the φC31 integrase enzyme, which was flanked by two nuclear localization signals. Expression of the egfp-zeocin fusion gene could be observed in transformed cells. The two plasmids were also transferred into silkworm eggs to obtain transgenic silkworms. Successful integration of the fusion gene was indicated by the detection of green fluorescence, which was emitted by the silkworms. Nucleotide sequence analysis demonstrated that the attB site had been cut, to allow recombination between the attB and endogenous pseudo attP sites in the cultured silkworm cells and silkworm individuals.

Advanced silk material spun by a transgenic silkworm promotes cell proliferation for biomedical application

Natural silk fiber spun by the silkworm Bombyx mori is widely used not only for textile materials, but also for biofunctional materials. In the present study, we genetically engineered an advanced silk material, named hSFSV, using a transgenic silkworm, in which the recombinant human acidic fibroblast growth factor (hFGF1) protein was specifically synthesized in the middle silk gland and secreted into the sericin layer to surround the silk fiber using our previously optimized sericin1 expression system. The content of the recombinant hFGF1 in the hSFSV silk was estimated to be approximate 0.07% of the cocoon shell weight. The mechanical properties of hSFSV raw silk fiber were enhanced slightly compared to those of the wild-type raw silk fiber, probably due to the presence of the recombinant of hFGF1 in the sericin layer. Remarkably, the hSFSV raw silk significantly stimulated the cell growth and proliferation of NIH/3T3 mouse embryonic fibroblast cells, suggesting that the mitogenic activity of recombinant hFGF1 was well maintained and functioned in the sericin layer of hSFSV raw silk. These results show that the genetically engineered raw silk hSFSV could be used directly as a fine biomedical material for mass application. In addition, the strategy whereby functional recombinant proteins are expressed in the sericin layer of silk might be used to create more genetically engineered silks with various biofunctions and applications.

Production of Bombyx mori silk fibroin incorporated with unnatural amino acids.

Silk fibroin incorporated with unnatural amino acids was produced by in vivo feeding of p-chloro-, p-bromo-, and p-azido-substituted analogues of L-phenylalanine (Phe) to transgenic silkworms (Bombyx mori) that expressed a mutant of phenylalanyl-tRNA synthetase with expanded substrate recognition capabilities in silk glands. Cutting down the content of Phe in the diet was effective for increasing the incorporation of Phe analogues but simultaneously caused a decrease of fibroin production. The azide groups incorporated in fibroin were active as chemical handles for click chemistry in both the solubilized and the solid (fibrous) states. The azides survived degumming in the boiling alkaline solution that is required for complete removal of the sericin layer, demonstrating that AzPhe-incorporated silk fibroin could be a versatile platform to produce "clickable" silk materials in various forms. This study indicates the huge potential of UAA mutagenesis as a novel methodology to alter the characteristics of B. mori silk.

A quicker degradation rate is yielded by a novel kind of transgenic silk fibroin consisting of shortened silk fibroin heavy chains fused with matrix metalloproteinase cleavage sites.

Degradation performance of silk fibroin is an important property for its medical applications. Herein we constructed a shortened silk fibroin heavy chain protein fused with a matrix metalloproteinase cleavage site (SSFH-MMP) along with a glutathione S-transferase tag ahead. The digestion assay shows it can be cut by matrix metalloproteinase-2 (MMP-2) at its MMP cleavage site. Furthermore, we introduced the SSFH-MMP into silk fibroin by genetic modification of silkworms in order to increase the degradation rate of the silk fibroin. After acquisition of a race of transgenic silkworms with the coding sequence of the MMP cleavage site in their genomic DNA, we tested some properties of their silk fibroin designated TSF-MMP. The results show that the TSF-MMP has MMP cleavage sites and yields a quicker degradation rate during dilution in MMP-2 enzyme buffer or implantation into tumor tissues compared with that of normal silk fibroin. Moreover, the TSF-MMP is in vitro non-toxic to humanbone marrow mesenchymal stem cells (hBM-MSCs) indicating that the TSF-MMP may become a biomaterial with a quicker degradation rate for its medical applications.

피브로인 H-chain 재조합 단백질 발현시스템을 이용한 청색형광단백질의 발현

ABSTRACT We produced the transgenic silkworm that expressed the enhanced blue fluorescent protein (EBFP) in the cocoon ofsilkworms. The EBFP fusion protein, each with N- and C-terminal sequences of the fibroin H-chain, was designed tobe secreted into the lumen of the posterior silk glands. The expression of the EBFP/H-chain fusion gene was regulatedby the fibroin H-chain promoter. The use of the 3×P3-driven DsRed2 cDNA as a marker allowed us to rapidly dis-tinguish transgenic silkworm. A mixture of the donor and helper vector was micro-injected into 300 eggs of silkworms,Baegokjam. We obtained 5 broods. The cocoon displayed blue fluorescence, proving that the fusion protein was presentin the cocoon. Also, the presence of fusion proteins in cocoons was demonstrated by SDS-PAGE and western blot anal-ysis. Accordingly, we suggest that the EBFP fluorescence silk will enable the production of the silk-based biomaterials. Key words : Fluorescent, Transgenic silkworm, EBFP, Bombyx mori, Silk

Postintegration stability of the silkworm piggyBac transposon

The piggyBac transposon is the most widely used vector for generating transgenic silkworms. The silkworm genome contains multiple piggyBac-like sequences that might influence the genetic stability of transgenic lines. To investigate the postintegration stability of piggyBac in silkworms, we used random insertion of the piggyBac [3 × p3 EGFP afm] vector to generate a W chromosome-linked transgenic silkworm, named W-T. Results of Southern blot and inverse PCR revealed the insertion of a single copy in the W chromosome of W-T at a standard TTAA insertion site. Investigation of 11 successive generations showed that all W-T females were EGFP positive and all males were EGFP negative; PCR revealed that the insertion site was unchanged in W-T offspring. These results suggested that endogenous piggyBac-like elements did not affect the stability of piggyBac inserted into the silkworm genome.

Overexpression and functional characterization of an Aspergillus niger phytase in the fat body of transgenic silkworm, Bombyx mori

In a previous study, we isolated 1,119 bp of upstream promoter sequence from Bmlp3, a gene encoding a member of the silkworm 30 K storage protein family, and demonstrated that it was sufficient to direct fat body-specific expression of a reporter gene in a transgenic silkworm, thus highlighting the potential use of this promoter for both functional genomics research and biotechnology applications. To test whether the Bmlp3 promoter can be used to produce recombinant proteins in the fat body of silkworm pupae, we generated a transgenic line of Bombyx mori which harbors a codon-optimized Aspergillus niger phytase gene (phyA) under the control of the Bmlp3 promoter. Here we show that the Bmlp3 promoter drives high levels of phyA expression in the fat body, and that the recombinant phyA protein is highly active (99.05 and 54.80 U/g in fat body extracts and fresh pupa, respectively). We also show that the recombinant phyA has two optimum pH ranges (1.5-2.0 and 5.5-6.0), and two optimum temperatures (55 and 37 °C). The activity of recombinant phyA was lost after high-temperature drying, but treating with boiling water was less harmful, its residual activity was approximately 84% of the level observed in untreated samples. These results offer an opportunity not only for better utilization of large amounts of silkworm pupae generated during silk production, but also provide a novel method for mass production of low-cost recombinant phytase using transgenic silkworms.

Reducing blood glucose levels in TIDM mice with an orally administered extract of sericin from hIGF-I-transgenic silkworm cocoons

In previous studies, we reported that the blood glucose levels of mice with type I diabetes mellitus (TIDM) was reduced with orally administered silk gland powder from silkworms transgenic for human insulin-like growth factor-I (hIGF-I). However, potential safety hazards could not be eliminated because the transgenic silk gland powder contained heterologous DNA, including the green fluorescent protein (gfp) and neomycin resistance (neo) genes. These shortcomings might be overcome if the recombinant hIGF-I were secreted into the sericin layer of the cocoon. In this study, silkworm eggs were transfected with a novel piggyBac transposon vector, pigA3GFP-serHS-hIGF-I-neo, containing the neo, gfp, and hIGF-I genes controlled by the sericin-1 (ser-1) promoter with the signal peptide DNA sequence of the fibrin heavy chain (Fib-H) and a helper plasmid containing the piggyBac transposase sequence under the control of the Bombyx mori actin 3 (A3) promoter, using sperm-mediated gene transfer to generate the transformed silkworms. The hIGF-I content estimated by enzyme-linked immunosorbent assay was approximately 162.7ng/g. To estimate the biological activity of the expressed hIGF-I, streptozotocin-induced TIDM mice were orally administered sericin from the transgenic silkworm. The blood glucose levels of the mice were significantly reduced, suggesting that the extract from the transgenic hIGF-I silkworm cocoons can be used as an orally administered drug.

Effect of ATG initiation codon context motifs on the efficiency of translation of mRNA derived from exogenous genes in the transgenic silkworm, Bombyx mori.

The context sequence motif surrounding the ATG initiation codon influences mRNA translation efficiency and affects protein production; however, the optimal sequence differs among species. To determine the optimal sequence for production of recombinant proteins in a transgenic silkworm, we compared 14-nucleotide context motifs around the ATG (ATG-context) in 50 silkworm genes and found the following consensus: (A/T)AN(A/T)ATCAAAatgN. We were also able to define the least-common motif: CCN(C/G)CGN(C/T/G)(G/C/T)(T/G)atgC, which served as a negative control. To examine the regulatory role of these motifs in protein expression, we constructed reporter plasmids containing different ATG-context motifs together with either the luciferase gene or an enhanced green fluorescent protein (EGFP) gene. These constructs were then used for comparison of luciferase reporter activity and EGFP production in BmN4 cells in vitro as well as in transgenic silkworms in vivo. We detected 10-fold higher luciferase activity in BmN4 cells transfected with the consensus ATG-context motif construct, compared to the negative control plasmid. ELISA measurements of EGFP translation products with the corresponding constructs in BmN4 cells showed consistently similar results. Interestingly, the translation efficiency of the novel consensus ATG-context motif did not show the highest activity in the transgenic silkworms in vivo, except for the fat body. The highest efficiency in the middle and posterior silk glands was produced by the sericin 1 context. Our results show that the ATG-context motifs differ among silkworm tissues. This result is important for the further improvement of the transgenic silkworm system for the production of recombinant proteins.

The progress and future of enhancing antiviral capacity by transgenic technology in the silkworm Bombyx mori

Bombyx mori is a common lepidopteran model and an important economic insect for silk production. B. mori nucleopolyhedrovirus (BmNPV) is a typical pathogenic baculovirus that causes serious economic losses in sericulture. B. mori and BmNPV are a model of insect host and pathogen interaction including invasion of the host by the pathogen, host response, and enhancement of host resistance. The antiviral capacity of silkworms can be improved by transgenic technology such as overexpression of an endogenous or exogenous antiviral gene, RNA interference of the BmNPV gene, or regulation of the immune pathway to inhibit BmNPV at different stages of infection. Antiviral capacity could be further increased by combining different methods. We discuss the future of an antiviral strategy in silkworm, including possible improvement of anti-BmNPV, the feasibility of constructing transgenic silkworms with resistance to multiple viruses, and the safety of transgenic silkworms. The silkworm model could provide a reference for disease control in other organisms.

Production of scFv-conjugated affinity silk film and its application to a novel enzyme-linked immunosorbent assay

Bombyx mori (silkworm) silk proteins have been utilized as unique biomaterials for various medical applications. To develop a novel affinity silk material, we generated a transgenic silkworm that spins silk protein containing the fibroin L-chain linked with the single-chain variable fragment (scFv) as a fusion protein. Previously, the scFv-conjugated “affinity” silk powder specifically immunoprecipitated its target protein, Wiskott-Aldrich syndrome protein. To expand the applicability of affinity silk materials, we processed the scFv-conjugated silk protein into a thin film by dissolving it in lithium bromide, then drying it in the wells of 96-well plates. Enzyme-linked immunosorbent assay demonstrated specific detection of Wiskott-Aldrich syndrome protein, both as a recombinant protein and in its native form extracted from mouse macrophages. These findings suggest that this scFv-conjugated silk film serves as the basis for an alternative immunodetection system.

Hormonal regulation and developmental role of Krüppel homolog 1, a repressor of metamorphosis, in the silkworm Bombyx mori

Juvenile hormone (JH) has an ability to repress the precocious metamorphosis of insects during their larval development. Krüppel homolog 1 (Kr-h1) is an early JH-inducible gene that mediates this action of JH; however, the fine hormonal regulation of Kr-h1 and the molecular mechanism underlying its antimetamorphic effect are little understood. In this study, we attempted to elucidate the hormonal regulation and developmental role of Kr-h1. We found that the expression of Kr-h1 in the epidermis of penultimate-instar larvae of the silkworm Bombyx mori was induced by JH secreted by the corpora allata (CA), whereas the CA were not involved in the transient induction of Kr-h1 at the prepupal stage. Tissue culture experiments suggested that the transient peak of Kr-h1 at the prepupal stage is likely to be induced cooperatively by JH derived from gland(s) other than the CA and the prepupal surge of ecdysteroid, although involvement of unknown factor(s) could not be ruled out. To elucidate the developmental role of Kr-h1, we generated transgenic silkworms overexpressing Kr-h1. The transgenic silkworms grew normally until the spinning stage, but their development was arrested at the prepupal stage. The transgenic silkworms from which the CA were removed in the penultimate instar did not undergo precocious pupation or larval–larval molt but fell into prepupal arrest. This result demonstrated that Kr-h1 is indeed involved in the repression of metamorphosis but that Kr-h1 alone is incapable of implementing normal larval molt. Moreover, the expression profiles and hormonal responses of early ecdysone-inducible genes (E74, E75, and Broad) in transgenic silkworms suggested that Kr-h1 is not involved in the JH-dependent modulation of these genes, which is associated with the control of metamorphosis.

Recombinant silk fibroin incorporated cell-adhesive sequences produced by transgenic silkworm as a possible candidate for use in vascular graft.

Interest in vascular grafts has recently grown because more patients are undergoing procedures that involve these grafts. However, smaller grafts with diameters <6 mm made from conventional biomaterials are associated with a high incidence of thrombosis, and therefore the development of improved materials suitable for small vascular grafts is highly desirable. In this paper, four kinds of recombinant Bombyx mori silk fibroins were prepared using transgenic techniques for use as silk vascular graft with a diameter of <6 mm. The peptide sequence TS(CDPGYIGSRAS)8 derived from the laminin B1 chain or the combination of two kinds of sequences, TS(CDPGYIGSRAS)8 and (TGRGDSPAS)8 derived from fibronectin, was incorporated into the light (L)-chain or the heavy (H)-chain of the silk fibroin. The fractions of the incorporated peptide sequences range from 0.8% to 7.2% by weight in the recombinant silk fibroins. This incorporation causes a very small increase in the random coil fraction of silk fibroin and a decrease in the tensile strength. Compared with native silk fibroin, the adhesive activities of mouse endothelial and smooth muscle cells increase significantly with the recombinant silk fibroin films incorporating only the TS(CDPGYIGSRAS)8 sequence independent of the L- or H-chains. A similar tendency was observed for the high migration activities of the endothelial cells in vitro and also the longer migration distance of the endothelial cell from the anastomotic part of rat abdominal aorta in vivo when this recombinant silk fibroin was used as a coating material for the silk graft. In view of the results, the recombinant silk fibroin incorporating the laminin peptide sequence can be potentially used as a vascular graft material.

Development of methods for risk assessment of transgenic silkworms rearing on biodiversity

Development of methods for risk assessment of transgenic silkworms rearing on biodiversity

Hox transcription factor Antp regulates sericin-1 gene expression in the terminal differentiated silk gland of Bombyx mori

Hox genes are well-known master regulators in developmental morphogenesis along the anteroposterior axis of animals. However, the molecular mechanisms by which Hox proteins regulate their target genes and determine cell fates are not fully understood. The silk gland of Bombyx mori is a tubular tissue divided into several subparts along the anteroposterior axis, and the silk genes are expressed with specific patterns. The sericin-1 gene (ser1) is expressed in the middle silk gland (MSG) with sublocal specificity. Here we show that the Hox protein Antp is a component of the middle silk gland-specific complex, MIC (MSG–intermolt-specific complex), binds to the essential promoter element of ser1, and activates its expression. Ectopic expression of Antp in transgenic silkworms induced the expression of ser1 in the posterior silk gland (PSG), but not in the anterior part of MSG (MSG-A). Correspondingly, a MIC-like complex was formed by the addition of recombinant Antp in extracts from PSG with its cofactors Exd and Hth, but not in extracts from MSG-A. Splicing patterns of ser1 mRNA induced by the ectopic expression of Antp in PSG were almost the same as those in MSG at the fifth instar and altered depending on the induction timing of Antp. Other Hox genes were expressed with sublocal specificity in the silk gland. The Bombyx silk gland might provide a useful system for understanding how Hox proteins select and regulate their target genes.

피브로인 H-chain 재조합 단백질 발현시스템을 이용한 녹색형광실크 생산

본 연구의 목적은 누에형질전환 기술을 이용하여 녹색형광실크를 개발하는 것으로서, 본 실험에서는 피브로인 H-chain의 N-말단과 C-말단을 이용하여 피브로인 재조합 단백질 발현 시스템을 제작하였고, 종결코돈이 없는 EGFP 유전자를 위의 발현 시스템에 클로닝하여 녹색형광실크를 제작하였다. 누에형질전환체 선발을 위해서는 3xP3 promoter와 DsRed2를 이용하여 선발하였고, 1200 개의 누에알에 microinjection 하여 F1 세대에서 8 bloods의 형질전환체를 선발하였다. 선발된 누에형질전환체는 초기배 단계의 눈과 신경조직, 유충과 번데기 그리고 성충의 눈에서 DsRed2 형광단백질이 발현되는 것을 확인 할 수 있었다. 또한 실크의 피브로인에서 EGFP 단백질이 발현되는 것을 확인하기 위해, F2세대의 누에형질전환체 중에서 5령 3일 유충을 해부하여 견사선을 형광현미경으로 관찰하였고, 중부와 후부 견사선에서 형광단백질이 발현되는 것을 확인할 수 있었다. 그리고 F2 세대의 고치와 저온에서 정련한 실크에서도 녹색형광단백질의 발현을 확인할 수 있었고, Western blot 분석에서도 EGFP 재조합 단백질이 피브로인 H-chain과 융합된 형태로 존재하는 것이 확인되었다. 이상의 결과에서 녹색형광실크를 생산하는 누에형질전환체가 성공적으로 제작 되었음을 확인할 수 있었고 이러한 결과를 토대로 새로운 산업소재로서 실크를 활용할 수 있을 것으로 기대한다. To express green fluorescent protein in the cocoon of silkworm, we constructed the fibroin H-chain expression system to produce enhanced green fluorescent protein (EGFP) in the cocoon of transgenic silkworms. The EGFP fusion protein, each with N- and C-terminal sequences of the fibroin H-chain, was designed to be secreted into the lumen of the posterior silk glands. The expression of the EGFP/H-chain fusion gene was regulated by the fibroin H-chain promoter. The use of the 3xP3-driven DsRed2 cDNA as a marker allowed us to rapidly distinguish transgenic silkworm. A mixture of the donor and helper vector was micro-injected into 1,200 eggs of bivoltin silkworms, Baegokjam. We obtained 8 broods. The cocoon displayed strong green fluorescence, proving that the fusion protein was present in the cocoon. Also, the presence of fusion proteins in cocoons was demonstrated by SDS-PAGE and immunoblotting. Accordingly, we suggest that the EGFP fluorescence silk will enable the production of the novel biomaterial based on the transgenic silk.

Expression system for production of bioactive compounds, recombinant human adiponectin, in the silk glands of transgenic silkworms

Adiponectin is an adipocyte hormone involved in glucose and lipid metabolism. The aim of this study was to develop a human adiponectin expression system in transgenic silkworm using a human adiponectin expression vector. The silk gland of the silkworm is a highly specialized organ that has the wonderful ability to synthesize and secrete silk protein. To express human adiponectin in the silk gland of transgenic silkworm, targeting vectors pB-A3-adiponectin-IRES-RFP and pB-Ser1-adiponectin-IRES-RFP were constructed and then introduced into the silkworm pupa. The transgenic silkworms were verified by PCR and then generated. The level of adiponectin in the transgenic silkworm was 6-10 ng/50 mg of freeze-dried powder, and western blotting using an antibody against human adiponectin demonstrated a specific band with a molecular weight of 30 kDa in the silkworm. These results showed that human adiponectin introduced into the silkworm genome was expressed successfully on a large-scale.

Establishment of transgenic silkworms expressing GAL4 specifically in the haemocyte oenocytoid cells

Insect haemocytes play significant roles in innate immunity. The silkworm, a lepidopteran species, is often selected as the model for studies into the functions of haemocytes in immunity; however, our understanding of the role of haemocytes remains limited because the lack of haemocyte promoters for transgene expression makes genetic manipulations difficult. In the present study, we aimed to establish transgenic silkworm strains expressing GAL4 in their haemocytes. First, we identified three genes with strong expression in haemocytes, namely, lp44, Haemocyte Protease 1 (HP1) and hemocytin. Transgenic silkworms expressing GAL4 under the control of the putative promoters of these genes were then established and expression was examined. Although GAL4 expression was not detected in haemocytes of HP1-GAL4 or hemocytin-GAL4 strains, lp44-GAL4 exhibited a high level of GAL4 expression, particularly in oenocytoids. GAL4 expression was also detected in the midgut but in no other tissues, indicating that GAL4 expression in this strain is mostly oenocytoid-specific. Thus, we have identified a promoter that enables oenocytoid expression of genes of interest. Additionally, the lp44-GAL4 strain could also be used for other types of research, such as the functional analysis of genes in oenocytoids, which would facilitate advances in our understanding of insect immunity.

Transgenics: Colored Fluorescent Silk Made by Transgenic Silkworms (Adv. Funct. Mater. 42/2013)

Transgenics: Colored Fluorescent Silk Made by Transgenic Silkworms (Adv. Funct. Mater. 42/2013)

Silk Gland Factor-2, Involved in Fibroin Gene Transcription, Consists of LIM Homeodomain, LIM-interacting, and Single-stranded DNA-binding Proteins

SGF-2 binds to promoter elements governing posterior silk gland-specific expression of the fibroin gene in Bombyx mori. We purified SGF-2 and showed that SGF-2 contains at least four gene products: the silkworm orthologues of LIM homeodomain protein Awh, LIM domain-binding protein (Ldb), a sequence-specific single-stranded DNA-binding protein (Lcaf), and the silk protein P25/fibrohexamerin (fhx). Using co-expression of these factors in Sf9 cells, Awh, Ldb, and Lcaf proteins were co-purified as a ternary complex that bound to the enhancer sequence in vitro. Lcaf interacts with Ldb as well as Awh through the conserved regions to mediate transcriptional activation in yeast. Misexpression of Awh in transgenic silkworms induces ectopic expression of the fibroin gene in the middle silk glands, where Ldb and Lcaf are expressed. Taken together, this study demonstrates that SGF-2 is a multisubunit activator complex containing Awh. Moreover, our results suggest that the Ldb·Lcaf protein complex serves as a scaffold to facilitate communication between transcriptional control elements.