Expression of Pax-3 in the lateral neural plate is dependent on a Wnt-mediated signal from posterior nonaxial mesoderm

During early patterning of the vertebrate neuraxis, the expression of the p aired-domain transcription factor Pax-3 is induced hn the lateral portions of the posterior neural plate via posteriorizing signals emanating from the late organizer and posterior nonaxial mesoderm. Using a dominant-negative approach, we show in explant assays that Pax-3 inductive activities from th e organizer do not depend on FGF,retinoic acid or XWnt-8 either alone or In combination, suggesting that the organizer map produce an unknown posterio rizing factor. However, Pax-3 inductive signals from posterior nonaxial mes oderm are Wnt-dependent. We show that Pax-3 expression in the lateral neura l plate expands in XWnt-8-injected embryos and is blocked by dominant-negat ive XWnt-8. Similarly, we show that the homeodomain transcription factor Ms x-1 which like Pax-3 is an early marker of the lateral neural plate, is ind uced by posterior nonaxial mesoderm and blocked by dominant-negative XWnt-8 . Finally, we show that Rohon-Beard primary neurons, a cell type that devel ops within the lateral neural plate, we also blocked in vivo by dominant-ne gative Xwnt-8. Together these data support a model in which patterning of t he lateral neural plate by Wnt-mediated signals is an early event that esta blishes a posteriolateral domain, marked by Pax-3 and Msx-1 expression, fro m which Rohon-Beard cells and neural crest will subsequently arise. (C) 199 9 Academie Press.