Oestrogen-related receptor reduces vitellogenin expression by crosstalk with the ecdysone receptor pathway in female silkworm, Bombyx mori.

Oestrogen-related receptor (ERR) is involved in oestrogen receptor (ER) signalling pathways owing to its similarity to ER in terms of domain structure and co-activator and response elements. Although insects lack ER, they harbour an ERR gene that is thought to modulate metabolism and energy conversion via an unknown mechanism. The present study investigated the function of ERR in insects using female silkworm (Bombyx mori, Bm). We found that the expression of B. mori vitellogenin (BmVg) and B. mori ERR (BmERR) in the fat bodies of female silkworms at different stages of development exhibited alternating patterns, and RNA interference of BmERR in females induced BmVg transcription, resulting in an increase in egg weight relative to the control. Furthermore, BmERR was found to be involved in regulating the transcription of BmVg through an oestrogen-related receptor response element (ERRE) in the promoter of the BmVg gene, as demonstrated by electrophoretic mobility shift assay, cell transfection assay and chromatin immunoprecipitation. In summary, our results indicate that BmERR bound to the ERRE motif in the BmVg promoter reducing the expression of BmVg in the fat body of the female silkworm. To our surprise, the ERRE also showed the ability to bind the ecdysone receptor (BmEcR) and ultraspiracle complex. Thus, we surmise that ERR participates in steroid hormone signalling by engaging in crosstalk with the ER pathway in vertebrates and with the EcR pathway in insects.