Cross-talk between juvenile hormone and ecdysone regulates transcription of fibroin modulator binding protein-1 in Bombyx mori.

Juvenile hormone (JH) and 20-hydroxyecdysone (20E) are the most important hormones in silkworm and play vital roles in silkworm development, metamorphosis, and silk protein synthesis. Fibroin modulator binding protein-1 (FMBP-1) is a novel transcription factor regulating fibroin heavy chain (fib-H) transcription in Bombyx mori. The roles of JH and 20E on FMBP-1 transcription are less known. Here, we show FMBP-1 transcription is repressed by juvenile hormone analog (JHA) and activated by 20E. We identify two Krüppel homolog 1 (Kr-h1) binding sites (KBS1 and KBS2) and an E74A binding site (EBS) in the promoter of FMBP-1. We demonstrate Kr-h1 directly binds to KBS1 and KBS2 to repress FMBP-1 transcription, and 20E promotes FMBP-1 transcription through E74A. In the presence of JH and 20E, E74A abolishes the repression of Kr-h1 and activates FMBP-1 transcription through direct binding to EBS between KBS1 and KBS2 in FMBP-1 promoter. Further, JHA and 20E treatment and RNA interference confirm the effects of JH and 20E on FMBP-1 transcription in vivo, thus affecting fib-H transcription. Our results reveal the molecular mechanism of FMBP-1 transcription regulated by the cross-talk between JH and 20E in Bombyx mori, and provide novel insights into FMBP-1 transcriptional regulation and silk protein synthesis.