Isolation and characterization of Urbain, a 20-hydroxyecdysone-inducible gene expressed during morphogenesis of Bombyx mori wing imaginal discs.

In insects, wing imaginal discs respond to the steroid hormone 20-hydroxyecdysone by initiating morphogenesis leading to the formation of the adult flight appendages. In this work we analyse the expression of a Bombyx gene, referred to as Urbain, whose cDNA had been previously isolated from wing discs (Chareyre et al. 1993). Accumulation of the 1.8 kb transcript occurs concomitantly with the increase of 20-hydroxyecdysone titer at every stage examined during post-embryonic development. In vitro, its accumulation is delayed 6-9 h after exposure to 20-hydroxyecdysone. Studies in the presence of cycloheximide have established that Urbain is a secondary response gene. The sequence of the mRNA contains a putative open reading frame of 1656 nucleotides encoding a secreted hydrophilic protein, and we suggest that the Urbain gene product plays a role in cellular mechanisms involved in morphogenesis of the epithelium.