Differential regulation of ecdysteroidogenic P450 gene expression in the silkworm, Bombyx mori

The regulatory mechanisms of ecdysteroidogenic P450 gene expression were investigated in the silkworm, Bombyx mori. Bommo-FMRFamide (BRFa), a neural suppressor of prothoracic gland (PG) activity, was found to suppress the expression of several P450 genes induced by prothoracicotropic hormone (PTTH) in the PG. A transcription inhibitor suppressed PTTH-induced expression of the P450 genes and the opposing effects of BRFa, while their short-term effects on ecdysteroidogenesis remained unchanged. This result suggests that the effects of these factors on the P450 gene transcripts become obvious on a longer time scale. Moreover, spontaneous expression of a P450 gene was observed in long-term PG culture, and was repressed by juvenile hormone. These results explain well the developmental fluctuation patterns of the P450 gene transcripts in the PG, indicating that multiple factors coordinate to regulate basal PG activity during insect development.