A biological timer in the fat body comprising Blimp-1, βFtz-f1 and Shade regulates pupation timing in Drosophila melanogaster.

During the development of multicellular organisms, many events occur with precise timing. In Drosophila melanogaster , pupation occurs about 12 hours after puparium formation, and its timing is believed to be determined by the release of a steroid hormone, ecdysone (E), from the prothoracic gland. Here, we demonstrate that the ecdysone-20-monooxygenase, Shade, determines the pupation timing by converting E to 20-hydroxyecdysone (20E) in the fat body, which is the organ that senses nutritional status. The timing of shade expression is determined by its transcriptional activator βFTZ-F1. The βFTZ-F1 gene is activated after a decline in the expression of its transcriptional repressor Blimp-1, which is temporally expressed around puparium formation in response to a high titer of 20E. The expression level and stability of Blimp-1 is critical for the precise timing of pupation. Thus, we propose that Blimp-1 molecules function as sands in an hourglass for this precise developmental timer system. Furthermore, our data suggest a biological advantage results from both the use of a transcriptional repressor for the time determination, and association of developmental timing with nutritional status of the organism.