Involvement of Frizzled-10 in Wnt-7a signaling during chick limb development

摘要

The dorsal ectoderm of the limb bud is known to regulate anterior-posterior patterning as well as dorsalventral patterning during Vertebrate limb morphogenesis. Wnt-7a, expressed in the dorsal ectoderm, encodes a key molecule implicated in these events. In the present study, chicken frizzled-lO (Fz-lO) encoding a Writ receptor was used to study mechanisms of Wnt-7a signaling during chick limb patterning, because its expression is restricted to the posterior-distal region of the dorsal limb bud. Fz-10 transcripts colocalize with Sonic hedgehog (Shh) in the dorsal side of stages 18-23 chick limb buds. It was demonstrated that Fz-lO interacts with Wnt-7a to induce synergistically the expression of Wnt-responsive genes, such as Siamois and Xnr3, in Xenopus animal cap assays. In the chick limb bud, Fz-10 expression is regulated by Shh and a signal from the dorsal ectoderm, presumably Wnt-7a, but not by signals from the apical ectodermal ridge. These results suggest that Fz-lO acts as a receptor for Wnt-7a and has a positive effect on Shh expression in the chick limb bud.