Yorkie overexpression in the posterior silk gland improves silk yield in Bombyx mori.

The traditional hybrid breeding techniques can no longer meet the increasing demands for silk production by the silkworm, Bombyx mori, and further improvement of the silk yield will depend on modern molecular breeding techniques. Here, we report improved silk yield in transgenic silkworms overexpressing the oncogene Yorkie specifically in the posterior silk gland (PSG). The Yorkie cDNA was ligated downstream of the hr3 enhancer and the fibroin L-chain (Fil) promoter, then inserted into a piggyBac vector for transgene. Overexpression of Yorkie in the PSG significantly increased the weight of the PSG, and also increased the weight of the cocoon, larval body, and pupal body to decreasing degrees. Overexpression of Yorkie up-regulated the Yorkie target genes resulting in increased cell size, endomitosis, the number of protein synthesis organelles, the expression of fibroin genes in the PSG, and eventually silk yield. Additionally, as we reported previously using the binary GAL4/UAS system, transgenic silkworms overexpressing Ras1 with the hr3 enhancer and the Fil promoter also showed improved silk yield. Unfortunately, the hybrid progeny of Yorkie-overexpressing silkworms and Ras1-overexpressing silkworms did not show overlapping improved silk yield due to the failure to increase expression of both Yorkie and Ras1.