Abstract: 【Aim】 Estradiol (E₂), an estrogen hormone, regulates the growth and reproduction through estrogen receptors (ERs) in vertebrates. There is no ER in insects, but studies showed that some insects can respond to E₂. In this study, the possible regulatory mechanisms of the expression of vitellogenin gene by E₂ was elucidated in the silkworm, Bombyx mori, after confirming that E₂ influenced the expression of BmVg in female larvae of the silkworm. 【Methods】 The expression level of BmVg was detected in the fat body of female larvae (60 h after mounting) of B. mori after in vitro treatment with different concentrations of E₂ (0.001, 0.05, 0.5, 5 and 50 nmol/L) by qRT-PCR, and the response of the silkworm to E₂ was analyzed. The ecdysone receptor gene of B. mori (BmEcRB1) was cloned and its prokaryotic expression vector was constructed. The BmEcRB1 protein was purified and incubated with E₂ in vitro, and the binding characteristics of E₂ to BmEcRB1 were assayed by microscale thermophoresis (MST). 【Results】 Different concentrations of E₂ significantly inhibited the expression of BmVg of female larvae of B. mori after in vitro culture, and the inhibitory effect was more obvious with the increase of E₂ concentration. MST results showed that E₂ had a certain affinity with BmEcRB1, with the dissociation constant (Kd) value of 77.8±22 μmol/L. 【Conclusion】 The results suggest that E₂ inhibits the expression of BmVg in the silkworm through competition with ecdysone to bind BmEcRB1.

Key words:  Bombyx mori, estradiol, ecdysone, vitellogenin, ecdysone receptor, gene expression, microscale thermophoresis (MST)