DIFFERENTIAL REQUIREMENTS FOR SEGMENT POLARITY GENES IN WINGLESS SIGNALING

The segment polarity genes wingless and engrailed are required through out development of Drosophila. During early embryogenesis, these two g enes are expressed in adjacent domains, in an inter-dependent way. Lat er, their expression is regulated by different mechanisms and becomes maintained by auto-regulation. To dissect the genetic requirements for the initial signaling between wingless and engrailed expressing cells , we have previously used a transgenic Drosophila strain that expresse s wingless under the control of the heat shock promoter (HS-wg). Focus ing on the later phases of wingless and engrailed regulation, we have now extended these studies, using embryos carrying various combination s of segment polarity mutations and the HS-wg transgene. We confirm so me of the existing models of regulation of the expression of wingless and engrailed. In addition, we find that HS-wg embryos require engrail ed for induction of ectopic endogenous wingless expression. Signaling from engrailed cells to this novel wingless expression domain is depen dent on hedgehog but also on porcupine. We further demonstrate a novel requirement for hedgehog in maintenance of expression of engrailed it self.