Overexpression of BmFoxO inhibited larval growth and promoted glucose synthesis and lipolysis in silkworm

Forkhead box O (FoxO) is a downstream transcription factor of the insulin-signaling pathway, which plays vital roles in the growth and metabolism of organisms. In this study, BmFoxO was overexpressed in BmE cells, in which proliferation was inhibited and apoptosis was increased. The transgenic vector overexpressing BmFoxO was constructed, and the transgenic silkworm line A4FoxO was generated via embryonic microinjection. The body size of A4FoxO silkworm was smaller than that of non-transgenic silkworm (WT). The quantitative polymerase chain reaction results revealed that the insulin pathway was enhanced and the growth-related TOR pathway was suppressed. Furthermore, the translation of proteins in the fat body of A4FoxO silkworm was inhibited. The expression level of genes involved in the glucose synthesis and lipolysis pathways was increased, whereas that of genes involved in fat synthesis was decreased. Oil red O staining revealed that the amount of lipid droplets was reduced in A4FoxO silkworms compared with WT. Further analysis showed that the content of triglyceride and glycogen was significantly decreased in fat body, but the content of glucose and trehalose was increased in the hemolymph of A4FoxO silkworms. These results suggest that the enhanced expression of BmFoxO disturbs glycolipid metabolism and affects silkworm growth.