Silkworms are economically important insects that have the ability to produce large amounts of silk. They have mass breeding methods and silk glands, which are specialized tissues that secrete silk fibroin and sericin. Thus, the production of recombinant proteins in a transgenic silkworm system is a promising approach. We developed a silkworm, Bombyx mori, as a host expression insect for recombinant proteins and successfully produced different proteins including antibodies, glycoproteins, and membrane receptors. The thyroid hormone receptor (TR) is a regulatory factor for many physiological phenomena. It is a lipophilic protein that has DNA-binding and ligand-binding domains. Based on our previous experiences, it was inferred that the recombinant TR easily formed aggregates and precipitates which is potentially due to an unstructured hinge domain. We applied the silkworm expression system to produce mice TRβ1 that was fused with glutathione S-transferase. Using 160 larvae, the yield of the recombinant GST-TRβ was approximately 4 mg, and the purified GST-TRβ completely retained its physiological activity. Our results indicated that the recombinant TRβ was secreted extracellularly using the silk fibroin signal peptide sequence. Moreover, we found that the expression system of silkworms was applicable to nuclear proteins.

蚕是经济上重要的昆虫，具有产生大量蚕丝的能力。他们有大量繁殖方法和丝腺，它们是分泌丝纤蛋白和丝胶蛋白的专门组织。因此，在转基因蚕系统中生产重组蛋白是一种有前途的方法。我们开发了一种蚕，家蚕作为重组蛋白的宿主表达昆虫，它成功地产生了包括抗体，糖蛋白和膜受体在内的各种蛋白。甲状腺激素受体（TR）是许多生理现象的调节因子。它是一种具有DNA结合和配体结合域的亲脂蛋白。根据我们以前的经验，推断重组TR容易形成聚集体和沉淀，这可能是由于非结构化铰链结构域所致。我们应用家蚕表达系统生产了与谷胱甘肽S-转移酶融合的小鼠TRβ1。使用160个幼虫，重组GST-TRβ的产量约为4 mg，纯化的GST-TRβ完全保留了其生理活性。我们的结果表明，重组TRβ是利用丝素蛋白信号肽序列在细胞外分泌的。此外，我们发现家蚕的表达系统适用于核蛋白。