The silk gland(SG)of the silkworm has significant potential for mass production of valuable recombinant proteins due to its convenient synthesis and secretion of silk proteins.In this study,we provided an alternative strategy to modify the original sericin-1 expression system.Transgenic silkworms were generated and the results showed that the DsRed was successfully expressed in MSG and secreted into the sericin layer; the modification of the vector resulted in a 4-fold increase of the recombinant RFP in transgenic silkworm,which leading the contents of recombinant RFP account for approximately 9.5%(w/w)of the cocoon weight.Then,several pharmaceutical protein genes for example the human growth factors(haFGF),human serum albumin(HSA),human superoxide dismutase(SOD)and subunit vaccine gene such as infectious bursal disease virus(IBDV)capsid protein VP2 were the sequence optimized and inserted into the modified sericin1 expression system to generate the original transgenic silkworms.Expressions of these genes in the cocoons of the transgenic silkworms were analyzed.Some of which for example the HSA,SOD and VP2 achieved highly efficient expression in cocoons which accounted for 17-40%of the total extracted cocoon proteins.For those targets with low expression level,we further developed a novel strategy by which the transgenic line was crossed with a PIG jumpstarter line to achieve the remobilization of the expression cassette to the “safe harbor” locus of genome for the efficient expression of the target gene.As a result of that,the expression of one target protein(haFGF)in the mutant line after hybridization with PIG jumpstarter achieved a significant increase comparing to the original line,which accounted for almost 26%weight of total extracted cocoon proteins.The high expression of recombinant proteins in cocoons facilitated their purifications that ultimately led the yield of the recombinant proteins with over 95%purity at milligram level.Next,some of the purified recombinant proteins were subjected for their bioactivity assay and checking their potential in biomaterials when combining with the silk fiber.For example,mitogenic activity and wound healing assays showed that the r-haFGF protein was bioactive to promote the growth,proliferation and migration of NIH/3T3 cells,which was equivalent to the commercial haFGF standard.Remarkably,the hFGF1 transgenic raw silk also significantly stimulated the cell growth and proliferation of mouse embryonic fibroblast cell(NIH/3T3),suggesting the mitogenic activity of recombinant hFGF1 was well maintained and functioned in the sericin layer of transgenic raw silk and the genetically engineered raw silk could be directly as a fine biomedical material for mass application.In conclusion,silk gland of silkworm combining with the jumpstarter-mediated remobilization could be as an efficient bioreactor strategy for recombinant production of bioactive proteins in the cocoons and the strategy by expression of functional recombinant proteins in the sericin layer of silk might be applicable to create more genetically engineered silks with various bio-functions and applications.