Wnt proteins have key roles in patterning of multicellular animals, acting at a distance from their sites of production. However, it is not well understood how these molecules propagate. This question has become even more puzzling by the discovery that Wnts harbour post-translational lipid-modifications, which enhance association with membranes and may therefore limit propagation by simple diffusion in an aqueous environment. The cellular mechanisms involved in Wnt propagation are largely unknown for vertebrate organisms. Here, I discuss my findings on the cellular localization of zebrafish Wnt8, as an example of a vertebrate Wnt. Wnt8 is a key signal for positioning the midbrain-hindbrain brain boundary (MHB) organizer along the anterior-posterior axis of the developing brain in vertebrates. However, it is not clear how this protein propagates from its source, the blastoderm margin, to the target cells, in the prospective neural plate. For this purpose, I have analysed a biologically active, fluorescently tagged Wnt8 in live zebrafish embryos. Wnt8 was present in live tissue in membrane associated punctate structures. In Wnt8 expressing cells these puncta localise to filopodial cellular processes, from which the protein is released to neighbouring cells. This filopodial release requires posttranslational palmitoylation. Although palmitoylation-defective Wnt8 retains auto- and juxtacrine signaling activity, it fails to signal over a long-range. Additionally, this Wnt8 palmitoylation is necessary for regulation of its neural plate target genes. These results suggest that vertebrate Wnt proteins use cell-to-cell contact through filopodia as a shortrange propagation mechanism while released palmitoylated Wnt is required for longrange signaling activity. Furthermore, I show that a Wnt8 receptor, Frizzled9 can negatively influence Wnt8 propagation and signaling range. Finally, I was able to determine the presence of an endogenous Wnt8 gradient in the neurectoderm. I discuss these findings in the context of Wnt8 signaling function in mediating anterior-posterior patterning during early brain development.

Wnt proteins have key roles in patterning of multicellular animals, acting at a distance from their sites of production. However, it is not well understood how these molecules propagate. This question has become even more puzzling by the discovery that Wnts harbour post-translational lipid-modifications, which enhance association with membranes and may therefore limit propagation by simple diffusion in an aqueous environment. The cellular mechanisms involved in Wnt propagation are largely unknown for vertebrate organisms. Here, I discuss my findings on the cellular localization of zebrafish Wnt8, as an example of a vertebrate Wnt. Wnt8 is a key signal for positioning the midbrain-hindbrain brain boundary (MHB) organizer along the anterior-posterior axis of the developing brain in vertebrates. However, it is not clear how this protein propagates from its source, the blastoderm margin, to the target cells, in the prospective neural plate. For this purpose, I have analysed a biologically active, fluorescently tagged Wnt8 in live zebrafish embryos. Wnt8 was present in live tissue in membrane associated punctate structures. In Wnt8 expressing cells these puncta localise to filopodial cellular processes, from which the protein is released to neighbouring cells. This filopodial release requires posttranslational palmitoylation. Although palmitoylation-defective Wnt8 retains auto- and juxtacrine signaling activity, it fails to signal over a long-range. Additionally, this Wnt8 palmitoylation is necessary for regulation of its neural plate target genes. These results suggest that vertebrate Wnt proteins use cell-to-cell contact through filopodia as a shortrange propagation mechanism while released palmitoylated Wnt is required for longrange signaling activity. Furthermore, I show that a Wnt8 receptor, Frizzled9 can negatively influence Wnt8 propagation and signaling range. Finally, I was able to determine the presence of an endogenous Wnt8 gradient in the neurectoderm. I discuss these findings in the context of Wnt8 signaling function in mediating anterior-posterior patterning during early brain development.