Signal transducer and activator of transcription is involved in the expression regulation of ecdysteroid-induced insulin-like growth factor-like peptide in the pupal wing disc of silkworm, Bombyx mori.

In insects, 20-hydroxyecdysone (20E) and insulin-like growth factor-like peptides (IGFLPs) regulate the development of imaginal discs. However, how IGFLPs are up-regulated to impact the development of the pupal wing disc is still unclear. In this study, we investigated the expression regulation of IGFLP in the pupal wing disc of silkworm, Bombyx mori. We confirmed that B. mori IGFLP (BmIGFLP) was mainly expressed in the pupal wing disc and the expression of BmIGFLP could be significantly induced by 20E. Bioinformatics analysis of BmIGFLP promoter sequence revealed three cis-regulation elements (CREs) of signal transducer and activator of transcription which is a key component in the Janus-activated kinase / pathway. Luciferase activity assays showed that two CREs enhanced the transcriptional activity of BmIGFLP. Electrophoretic mobility shift and chromatin immunoprecipitation assays demonstrated that proteins in the nuclear extracts of B. mori pupal wing discs and BmN cells could only bind to the duanyu1813 CRE3, indicating that duanyu1813 CRE3 activated by Bmduanyu1813 enhances BmIGFLP expression at pupal stages. Although 20E could not enhance the expression of 20E enhanced the nucleus translocation of Bmduanyu1813 to bind with the duanyu1813 CRE3 in the BmIGFLP promoter. The increase of transcriptional activity of the duanyu1813 CRE3 by overexpression of Bmduanyu1813 and addition of 20E in BmN cells confirmed this result. Taken together, all data indicate that Bmduanyu1813 is one of the transcription factors activating 20E-induced BmIGFLP expression in the pupal wing disc.

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