Potential role for a FTZ-F1 steroid receptor superfamily member in the control of Drosophila metamorphosis.

FTZ-F1, a member of the steroid receptor superfamily, has been implicated in the activation of the homeobox segmentation gene fushi tarazu early in Drosophila embryogenesis. We have cloned a developmental isoform of FTZ-F1 and found that it is expressed as a product of the previously identified, midprepupal chromosome puff at 75CD. The 75CD puff occurs in the midst of a period of intense puffing activity that is triggered in response to the steroid hormone ecdysone at the onset of metamorphosis. Indirect immunofluorescent staining for FTZ-F1 on Drosophila polytene chromosomes reveals binding to over 150 chromosomal targets, which include 75CD itself and prominent late prepupal puffs that are predicted to be regulated by midprepupal puff proteins. These results suggest a role for FTZ-F1 as a regulator of insect metamorphosis and underscore the repeated utilization of a regulatory protein for widely separate developmental pathways.