Department of Zoology, University of Wisconsin, Madison, Wisconsin, United States of America.
PLoS Genet. 2012;8(2):e1002503. doi: 10.1371/journal.pgen.1002503. Epub 2012 Feb 23.
Proper assignment of cellular fates relies on correct interpretation of Wnt and Hedgehog (Hh) signals. Members of the Wnt Inhibitory Factor-1 (WIF1) family are secreted modulators of these extracellular signaling pathways. Vertebrate WIF1 binds Wnts and inhibits their signaling, but its Drosophila melanogaster ortholog Shifted (Shf) binds Hh and extends the range of Hh activity in the developing D. melanogaster wing. Shf activity is thought to depend on reinforcing interactions between Hh and glypican HSPGs. Using zebrafish embryos and the heterologous system provided by D. melanogaster wing, we report on the contribution of glypican HSPGs to the Wnt-inhibiting activity of zebrafish Wif1 and on the protein domains responsible for the differences in Wif1 and Shf specificity. We show that Wif1 strengthens interactions between Wnt and glypicans, modulating the biphasic action of glypicans towards Wnt inhibition; conversely, glypicans and the glypican-binding "EGF-like" domains of Wif1 are required for Wif1's full Wnt-inhibiting activity. Chimeric constructs between Wif1 and Shf were used to investigate their specificities for Wnt and Hh signaling. Full Wnt inhibition required the "WIF" domain of Wif1, and the HSPG-binding EGF-like domains of either Wif1 or Shf. Full promotion of Hh signaling requires both the EGF-like domains of Shf and the WIF domains of either Wif1 or Shf. That the Wif1 WIF domain can increase the Hh promoting activity of Shf's EGF domains suggests it is capable of interacting with Hh. In fact, full-length Wif1 affected distribution and signaling of Hh in D. melanogaster, albeit weakly, suggesting a possible role for Wif1 as a modulator of vertebrate Hh signaling.
细胞命运的正确分配依赖于对 Wnt 和 Hedgehog（Hh）信号的正确解读。Wnt 抑制因子-1（WIF1）家族的成员是这些细胞外信号通路的分泌调节剂。脊椎动物 WIF1 结合 Wnts 并抑制其信号传导，但它的果蝇同源物 Shifted（Shf）结合 Hh 并扩展了 Hh 在发育中的果蝇翅膀中的活性范围。Shf 活性被认为依赖于 Hh 和糖蛋白 HSPGs 之间的强化相互作用。我们使用斑马鱼胚胎和果蝇翅膀提供的异源系统，报告了糖蛋白 HSPGs 对斑马鱼 Wif1 的 Wnt 抑制活性的贡献，以及负责 Wif1 和 Shf 特异性差异的蛋白质结构域。我们表明 Wif1 增强了 Wnt 与糖蛋白之间的相互作用，调节了糖蛋白对 Wnt 抑制的双相作用；相反，糖蛋白和 Wif1 的糖蛋白结合“EGF 样”结构域是 Wif1 完全 Wnt 抑制活性所必需的。我们使用 Wif1 和 Shf 之间的嵌合构建体来研究它们对 Wnt 和 Hh 信号的特异性。完全的 Wnt 抑制需要 Wif1 的“WIF”结构域，以及 Wif1 或 Shf 的 HSPG 结合 EGF 样结构域。完全促进 Hh 信号需要 Shf 的 EGF 样结构域和 Wif1 或 Shf 的 WIF 结构域。Wif1 的 WIF 结构域可以增加 Shf 的 EGF 结构域促进 Hh 信号的活性表明它能够与 Hh 相互作用。事实上，全长 Wif1 以微弱的方式影响了果蝇中 Hh 的分布和信号传导，这表明 Wif1 可能作为脊椎动物 Hh 信号的调节剂发挥作用。
