Nuclear hormone receptor BmFTZ-F1 is involved in regulating the fibroin heavy chain gene in the silkworm, Bombyx mori

• Published in: Biochimica et biophysica acta 2016-11, Vol.1860 (11), p.2529-2536
• Main Authors: Zhou, Chunyan, Zha, Xingfu, Shi, Panpan, Zhao, Peng, Wang, He, Zheng, Renwen, Xia, Qingyou
• Format: Article
• Language: English
• Subjects: 20-Hydroxyecdysone; Animals; Bombyx - genetics; Bombyx - metabolism; DNA-Binding Proteins - genetics; DNA-Binding Proteins - metabolism; Ecdysterone - pharmacology; Exocrine Glands - drug effects; Exocrine Glands - metabolism; Fibroin heavy chain; Fibroins - genetics; Fibroins - metabolism; FTZ-F1; Insect Proteins - genetics; Insect Proteins - metabolism; Nuclear hormone receptor; Protein Binding; Response Elements; Transcription Factors - genetics; Transcription Factors - metabolism
• ISSN: 0304-4165; 0006-3002; 1872-8006
• DOI: 10.1016/j.bbagen.2016.07.025

The synthesis of silk protein is controlled by hormones. The expression of the nuclear hormone Bmftz-f1 in the posterior silk gland (PSG) is induced by 20-hydroxyecdysone in vivo and in vitro. However, whether Bmftz-f1 regulates silk protein expression is unknown. In our study, western blotting and quantitative polymerase chain reactions were conducted to detect the expression of FTZ-F1 in the PSG. Electrophoretic mobility shift, chromatin immunoprecipitation, far-western blotting, bimolecular fluorescence complementation, and dual luciferase reporter assays were performed to investigate the effect of FTZ-F1 on the fibH promoter. (1) The expression of the hormone receptor BmFTZ-F1 was opposite to that of fibH. It was highly expressed in the PSG during the fourth molting stage and the beginning of the fifth instar, and then its expression decreased gradually until it disappeared at the end of the fifth instar and the wandering stage. (2) We identified a FTZ-F1 response element 390bp upstream of the transcription initiation site of the fibH promoter. (3) BmFTZ-F1 interacted with the basic helix-loop-helix transcription factor Bmdimm. (4) BmFTZ-F1 down-regulated fibH promoter activity and counteracted the effect of Bmdimm on fibH expression. Integrating these results, we conclude that BmFTZ-F1 regulates the transcription of fibH by binding to the FTZ-F1 response element in the fibH promoter and counteracts the effect of Bmdimm on fibH expression. These findings provide new insights into the mechanism of regulation of the silk protein gene. •Bmftz-f1 is a developmental stage-specific transcription factor in the PSG of B. mori.•BmFTZ-F1 regulates the transcription of fibH by binding to an FTZ-F1 response element.•BmFTZ-F1 is a negative regulator of fibH.•BmFTZ-F1 counteracts the effect of Bmdimm on fibH by interacting with Bmdimm.