Overexpression of recombinant infectious bursal disease virus (IBDV) capsid protein VP2 in the middle silk gland of transgenic silkworm.

Infectious bursal disease virus (IBDV) is the causative agent of a highly contagious disease affecting young chickens and causes serious economic losses to the poultry industry worldwide. Development of subunit vaccine using its major caspid protein, VP2, is one of the promising strategies to protect against IBDV. This study aim to test the feasibility of using silkworm to produce recombinant VP2 protein (rVP2) derived from a very virulent strain of IBDV (vvIBDV). A total of 16 transgenic silkworm lines harboring a codon-optimized VP2 gene driven by the sericin1 promoter were generated and analyzed. The results showed that the rVP2 was synthesized in the middle silk gland of all lines and secreted into their cocoons. The content of rVP2 in the cocoon of each line was ranged from 0.07 to 16.10 % of the total soluble proteins. The rVP2 was purified from 30 g cocoon powders with a yield of 3.33 mg and a purity >90 %. Further analysis indicated that the rVP2 was able to tolerate high temperatures up to 80 °C, and exhibited specific immunogenic activity in mice. To our knowledge, this is the first report of overexpressing rVP2 in the middle silk gland of transgenic silkworm, which demonstrates the capability of silkworm as an efficient tool to produce recombinant immunogens for use in new vaccines against animal diseases.

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.