βFTZ-F1 dependent and independent activation of Edg78E, a pupal cuticle gene, during the early metamorphic period in Drosophila melanogaster

Insect metamorphosis is a developmentally important event for formation of adult structures from larval imaginal cells, and it is controlled by the ecdysteroid hormone. At the onset of metamorphosis, both the cuticle gene Edg78E and the transcription factor βFTZ-F1 are expressed during the mid- to late prepupal period after a large ecdysteroid pulse. Edg78E mRNA is inducible by premature expression of βFTZ-F1 and the Edg78E expression level is reduced in an ftz-f1 mutant. Using a transgenic fly reporter assay, a 1.2 kb promoter region of the Edg78E gene has been identified, which was sufficient for appropriate temporally and spatially specific expression of the reporter gene LacZ. Within the promoter region, two βFTZ-F1 binding sites are present and disruption of these sites reduced the expression level of the reporter gene. LacZ expression levels were dramatically reduced in the head and thorax regions but not affected in the abdominal region, suggesting that βFTZ-F1 is required for high-level Edg78E expression specifically in the head and thorax regions. The findings suggest that βFTZ-F1 is a regulator for temporal gene expression at the onset of metamorphosis, and that complex mechanisms regulate the temporal and spatial regulation of gene expression during metamorphosis.