Regulatory mechanisms of ecdysone-inducible Blimp-1 encoding a transcriptional repressor that is important for the prepupal development in Drosophila

Blimp-1 is an ecdysone-inducible transcription factor that is expressed in the early stage of the prepupal period. The timing of its disappearance determines expression timing of the FTZ-F1 gene, whose temporally restricted expression is essential for the prepupal development. To elucidate the termination mechanism of Blimp-1 gene expression, we examined the regulation of the Blimp-1 gene using an organ culture system. The results showed that the Blimp-1 gene is transcribed in cultured organs taken from a low ecdysteroid period even after extended exposure to 20-hydroxyecdysone, while well-known early genes such as E75A are repressed under the same conditions. Similar selective transcription was observed in the cultured organs obtained from a high ecdysteroid period. We further showed that Blimp-1 transcripts quickly disappeared in the presence of actinomycin D. From these results, we concluded that the Blimp-1 gene is transcribed when the ecdysteroid titer is high, but the expressed mRNA degrades rapidly; these unique regulations limit its expression to the high ecdysteroid stage.