Effects of Osiris9a on Silk Properties in Determined by Transgenic Overexpression.

Osiris is an insect-specific gene family with multiple biological roles in development, phenotypic polymorphism, and protection. In the silkworm, we have previously identified twenty-five Osiris genes with high evolutionary conservation and remarkable synteny among several insects. () is expressed only in the silk gland, particularly in the middle silk gland (MSG). However, the biological function of BmOsi9a is still unknown. In this study, we overexpressed in the silk gland by germline transgene expression. was overexpressed not only in the MSG but also in the posterior silk gland (PSG). Interestingly, could be secreted into the lumen in the MSG but not in the PSG. In the silk fiber, overexpressed interacted with Sericin1 in the MSG, as confirmed by a co-immunoprecipitation assay. The overexpression of altered the secondary structure and crystallinity of the silk fiber, thereby changing the mechanical properties. These results provide insight into the mechanisms underlying silk proteins secretion and silk fiber formation.