BmYki is transcribed into four functional splicing isoforms in the silk glands of the silkworm Bombyx mori

Yorkie (Yki), the Drosophila homolog of vertebrate yes-associated protein (YAP), is a key effector of the Hippo pathway, which modulates organ size via the transcriptional regulation of downstream targets involved in cell proliferation and survival. YAP has been shown to be expressed as multiple splicing isoforms in mammals, but thus far, no evidence of alternatively spliced Yki isoforms has been reported in insects. Here, we confirmed that the Yki protein of the silkworm Bombyx mori, BmYki, is transcribed in the silk gland into at least four splicing isoforms, named BmY1329, BmY1314, BmY1188, and BmY1173. Further analysis revealed that BmY1329 and BmY1314 each contain two WW domains, whereas BmY1188 and BmY1173 each contain only one WW domain. Each BmYki isoform functions in regulating expression of Yki target genes in cultured B. mori embryonic cells, and exhibits a few different effects on the expression of Yki targets. Interestingly, the expression of silk fibroin protein genes could also be influenced by each of the BmYki isoforms, suggesting that BmYki is involved in the regulation of silk protein-coding genes. This study provides novel insights into the role of BmYki. The contribution of each BmYki isoform to the modulation of gene expression will be of great interest for further study.