Extracellular regulation of hedgehog and Wnt signaling during Drosophila wing development

Cell-bound members of the Heparan Sulfate Proteoglycan (HSPG) family such as such as Daily and Dlp are extracellular agents required for normal Hh activity. HSPGs are implicated during Hh transport through the tissues and in Hh reception. According to the prevailing view the physical affiliation between HSPGs and Hh requires a secreted protein encoded by shifted (shf). As expected the diffusion of tagged Hh is strongly reduced in shf mutants. Loss of Shf or HSPGs also leads to strong reductions in Hh accumulation. Despite these advances several questions remain to be answered. Firstly, it is unclear whether normal Hh accumulation by Shf/HSPGs is a pre-requisite for normal Hh signaling. Secondly, despite the lack of shf or HSPGs, Hh continues to signal at short-range, suggesting that Hh movement is not completely perturbed, indicating that for Shf or HSPGs may be dispensable for Hh signaling at short-range. Thirdly, at high levels Hh does not require Shf to elicit response in target cells, suggesting that Hh may signal independently of Shf. In Chapter 1 we show that Dlp maintain short-range Hh signaling independently of Shf, indicating that Shf is dispensable for short-range Hh signaling. Interestingly, shf discs with raised Hh do not show corresponding increases in long-range Hh signaling. We provide evidence that implicates the role for Shf during Hh reception in areas where Hh levels are expected to be low. Finally we observe that increases in Hh signaling range does not require normal Hh accumulation and vise versa. We propose that normal Hh reception is more essential than normal Hh accumulation.;A vertebrate ortholog of Shf, the Wnt Inhibitory Factor-1 (WIF-1) has no known role in Hedgehog signaling. Instead, WIF-1 binds and inhibits vertebrate Wnts, and also inhibits Drosophila Wnt member Wingless (Wg), in all circumstances by an unknown mechanism. In contrast, Shf has no known role during Wg signaling. It remains in question whether WIF-1 and Shf have overlapping roles. Therefore we ask whether WIF-1 has a role in Hh signaling, and whether Shf may influence signaling by Wg. We find that HSPGs render WIFI-1 more effective in inhibiting Wnt/Wg in both vertebrates and flies. We also show that the vertebrate Wnt-binding WIF domain helps Hh signaling. Finally, we provide genetic evidence that implicates Shf involvement during Wg signaling. Together these findings reveal unexpected and overlapping roles between WIF-1 and Shf.