Wingless capture by Frizzled and Frizzled2 in Drosophila embryos

A variety of factors could influence how far developmental signals spread. For example, the Patched receptor limits the range of its ligand Hedgehog. Somehow, the Frizzled2 receptor has the opposite effect on its ligand. Incr easing the level of Frizzled2 stabilizes Wingless and thus extends the Wing less gradient in Drosophila wing imaginal disks. Here we ask whether Frizzl ed or Frizzled2 affects the spread of Wingless in Drosophila embryos. We sh ow that in the embryonic epidermis, the combined expression of both recepto rs is lowest in the engrailed domain. This is because expression of Frizzle d is repressed by the Engrailed transcription factor, whereas that of Frizz led2 is repressed by Wingless signaling. Receptor downregulation correlates with an early asymmetry in Wingless distribution, characterized by the los s of Wingless staining in the engrailed domain. Raising the expression of e ither Frizzled or Frizzled2 in this domain prevents the early disappearance of Wingless-containing vesicles. Apparently, Wingless is captured, stabili zed, and quickly internalized by either receptor. As far as we can tell, ca ptured Wingless is not passed on to further cells and does not contribute t o the spread of Wingless. Receptor downregulation in the posterior compartm ent may contribute to dampening the signal at the time when cuticular fates are specified. (C) 2001 Academic Press.