The Broad Complex isoform 2 (BrC-Z2) transcriptional factor plays a critical role in vitellogenin transcription in the silkworm Bombyx mori

Abstract

Background: Vitellogenin (Vg) is synthesized in the fat body of the female silkworm Bombyx mori and transported to the oocyte as a source of nutrition for embryo development. It is well known that ecdysone regulates physiological, developmental and behavioral events in silkworm. However, it is still not clear how the ecdysone regulates B. mori Vg (BmVg) transcription.

Methods: Electrophoretic mobility shift assay (EMSA) and cell transfection assay were used to reveal whether BmBrC-Z2 is involved in regulating BmVg transcription. RNAi was employed to illustrate the function of BmBrC-Z2 in the silkworm egg formation and development.

Results: (1) The transcription of BmVg can be induced by ecdysone in the female fat body. (2) Three putative BrC-Z2 cis-response elements were mapped to regions flanking the BmVg gene. (3) BmBrC-Z2 required direct binding to the cis-response elements on the BmVg promoter. (4) Over-expression of three BmBrC isoforms in the cell line showed that only BmBrC-Z2 could induce the BmVg promoter activity. (5) RNA interference (RNAi) of BmBrC-Z2 in female remarkably reduced BmVg synthesis and led to destructive affection on egg formation. The dsRNA of BmBrC-Z2 treated moths laid fewer and whiter eggs compared to the control.

Conclusions: BmBrC-Z2 transported the ecdysone signal then regulated BmVg transcription directly to control vitellogenesis and egg formation in the silkworm.

General significance: The results of this study revealed that BmBrC-Z2 as a key factor to mediate ecdysone regulates reproduction in the silkworm.

Keywords: Bombyx mori; Broad Complex; Ecdysone; Vitellogenin.