Temporally restricted expression of transcription factor beta FTZ-F1: significance for embryogenesis, molting and metamorphosis in Drosophila melanogaster

FTZ-F1, a member of the nuclear receptor superfamily, has been implicated i n the activation of the segmentation gene fushi tarazu during early embryog enesis of Drosophila melanogaster, We found that an isoform of FTZ-F1, beta FTZ-F1, is expressed in the nuclei of almost all tissues slightly before t he first and second larval ecdysis and before pupation, Severely affected f tz-f1 mutants display an embryonic lethal phenotype, but can be rescued by ectopic expression of beta FTZ-F1 during the period of endogenous beta FTZ- F1 expression in the wild type. The resulting larvae are not able to molt, but this activity is rescued again by forced expression of beta FTZ-F1, all owing progression to the next larval instar stage. On the other hand, prema ture expression of beta FTZ-F1 in wild-type larvae at mid-first instar or m id-second instar stages causes defects in the molting process. Sensitive pe riods were found to be around the time of peak ecdysteroid levels and sligh tly before the start of endogenous beta FTZ-F1 expression. A hypomorphic ft z-f1 mutant that arrests in the prepupal stage can also be rescued by ectop ic, time-specific expression of beta FTZ-F1, Failure of salivary gland hist olysis, one of the phenotypes of the ftz-f1 mutant, is rescued by forced ex pression of the ftz-f1 downstream gene BR-C during the late prepupal period , These results suggest that beta FTZ-F1 regulates genes associated with ec dysis and metamorphosis, and that the exact timing of its action in the ecd ysone-induced gene cascade is important for proper development.