Expression of the hIGF-I gene driven by the Fhx/P25 promoter in the silk glands of germline silkworm and transformed BmN cells

P25 Gene Knockout Contributes to Human Epidermal Growth Factor Production in Transgenic Silkworms

Transgenic silkworm expression systems have been applied for producing various recombinant proteins. Knocking out or downregulating an endogenous silk protein is considered a viable strategy for improving the ability of transgenic expression systems to produce exogenous proteins. Here, we report the expression of human epidermal growth factor (hEGF) in a P25 gene knockout silkworm. The hEGF gene regulated by the P25 gene promoter was integrated into a silkworm's genome. Five transgenic positive silkworm lineages were generated with different insertion sites on silkworm chromosomes and the ability to synthesize and secrete proteins into cocoons. Then, a cross-strategy was used to produce transgenic silkworms with a P25 gene knockout background. The results of the protein analysis showed that the loss of an endogenous P25 protein can increase the hEGF production to about 2.2-fold more than normal silkworms. Compared to those of transgenic silkworms with wild type (non-knockout) background, the morphology and secondary structure of cocoon silks were barely changed in transgenic silkworms with a P25 gene knockout background, indicating their similar physical properties of cocoon silks. In conclusion, P25 gene knockout silkworms may become an efficient bioreactor for the production of exogenous proteins and a promising tool for producing various protein-containing silk biomaterials.

Human epidermal growth factor-functionalized cocoon silk with improved cell proliferation activity for the fabrication of wound dressings

Human epidermal growth factor (hEGF) is a key factor involved in wound healing owing to its powerful ability to stimulate cell proliferation. In this study, we used piggyBac transposon technology to produce transgenic silkworms expressing the hEGF protein fused to truncated heavy chain (FibH-hEGF). The FibH-hEGF fusion protein was successfully expressed and secreted into silkworm cocoons. Compared to wild-type silk, the transgenic silkworm silk had the similar morphology about silks fiber surface and cocoon nets, while the secondary structure between the transgenic silk and wild-type silk was different. Most importantly, transgenic silkworm cocoon silk powder extract significantly increased human fibroblast FIB cell proliferation for a long duration with no apparent cytotoxicity. Our study provides a promising method for obtaining cost-effective and functional biomaterials for the fabrication of wound dressings.

Genetic engineered color silk: fabrication of a photonics material through a bioassisted technology

Silk produced by the silkworm Bombyx mori is an attractive material because of its luster, smooth and soft texture, conspicuous mechanical strength, good biocompatibility, slow biodegradation, and carbon neutral synthesis. Silkworms have been domesticated and bred for production of better quality and quantity of silk, resulting in the development of sericulture and the textile industry. Silk is generally white, so dyeing is required to obtain colored fiber. However, the dyeing process involves harsh conditions and generates a large volume of waste water, which have environmentally and economically negative impacts. Although some strains produce cocoons that contain pigments derived from the mulberry leaves that they eat, the pigments are distributed in the sericin layer and are lost during gumming. In trials for production of colored silk by feeding silkworms on diets containing dyes, only limited species of dye molecules were incorporated into the silk threads. A method for the generation of transgenic silkworm was established in conjunction with the discovery of green fluorescent protein (GFP), and silkworms carrying the GFP gene spun silk threads that formed cocoons that glowed bright green and still retained the original properties of silk. A wide range of color variation of silk threads has been obtained by replacing the GFP gene with the genes of other fluorescent proteins chosen from the fluorescent protein palette. The genetically modified silk with photonic properties can be processed to form various products including linear threads, 2D fabrics, and 3D materials. The transgenic colored silk could be economically advantageous due to addition of a new value to silk and reduction of cost for water waste, and environmentally preferable for saving water. Here, I review the literature regarding the production methods of fluorescent silk from transgenic silkworms and present examples of genetically modified color silk.

High yield exogenous protein HPL production in the Bombyx mori silk gland provides novel insight into recombinant expression systems

The silk gland of Bombyx mori (BmSG) has gained significant attention by dint of superior synthesis and secretion of proteins. However, the application of BmSG bioreactor is still a controversial issue because of low yields of recombinant proteins. Here, a 3057 bp full-length coding sequence of Hpl was designed and transformed into the silkworm genome, and then the mutant (Hpl/Hpl) with specific expression of Hpl in posterior BmSG (BmPSG) was obtained. In the mutants, the transcription level of Fib-L and P25, and corresponding encoding proteins, did not decrease. However, the mRNA level of Fib-H was reduced by 71.1%, and Fib-H protein in the secreted fibroin was decreased from 91.86% to 71.01%. The mRNA level of Hpl was 0.73% and 0.74% of Fib-H and Fib-L, respectively, while HPL protein accounted for 18.85% of fibroin and 15.46% of the total amount of secreted silk protein. The exogenous protein was therefore very efficiently translated and secreted. Further analysis of differentially expressed gene (DEG) was carried out in the BmPSG cells and 891 DEGs were detected, of which 208 genes were related to protein metabolism. Reduced expression of endogenous silk proteins in the BmPSG could effectively improve the production efficiency of recombinant exogenous proteins.

The advances and perspectives of recombinant protein production in the silk gland of silkworm Bombyx mori

The silk gland of silkworm Bombyx mori, is one of the most important organs that has been fully studied and utilized so far. It contributes finest silk fibers to humankind. The silk gland has excellent ability of synthesizing silk proteins and is a kind tool to produce some useful recombinant proteins, which can be widely used in the biological, biotechnical and pharmaceutical application fields. It's a very active area to express recombinant proteins using the silk gland as a bioreactor, and great progress has been achieved recently. This review recapitulates the progress of producing recombinant proteins and silk-based biomaterials in the silk gland of silkworm in addition to the construction of expression systems. Current challenges and future trends in the production of valuable recombinant proteins using transgenic silkworms are also discussed.

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 162.7 ng/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.

Methods for sperm-mediated gene transfer

The transgenic technologies represent potent biotechnological tools that allow the generation of genetically modified animals useful for basic research and for biomedical, veterinary, and agricultural applications. Among transgenic techniques, we describe here the sperm-mediated gene transfer methods that is gene transfer based on the spontaneous ability of sperm cells to bind and internalize exogenous DNA and to carry it to oocyte during fertilization, producing genetically modified animals with high efficiency.

Lowering the blood glucose of diabetes mellitus mice by oral administration with transgenic human insulin-like growth factor I silkworms

To evaluate the biological activity of the posterior silk glands of transgenic silkworms expressing human insulin-like growth factor I (hIGF-I), we bred hIGF-I-transgenic silkworms through eight generations by continuously selecting with green fluorescence and G418. The G8 transgenic silkworms were confirmed by polymerase chain reaction and dot blotting, and their posterior silk glands were removed from the fifth instar larvae to make freeze-dried powders. Enzyme-linked immunosorbent assay results showed that the expression level of hIGF-I in the posterior silk glands of G8 transgenic silkworm is approximately 493 ng/g of freeze-dried powder. When the freeze-dried powder was administrated by gavage to diabetes mellitus (DM) mice, the blood glucose in DM mice significantly decreased (P < 0.05) in a time- and dose-dependent manner compared with that of DM mice orally administrated with distilled water and normal freeze-dried powders made of untreated silk glands. These results demonstrated that hIGF-I expressed in posterior silk glands of transgenic silkworms could reduce blood glucose by oral administration.