A new Transgenic Reporter Line Reveals Wnt-dependent Snai2 Re-expression and Cranial Neural Crest Differentiation in Xenopus

During vertebrate embryogenesis, the cranial neural crest (CNC) forms at the neural plate border and subsequently migrates and diferentiates into many types of cells. The transcription factor Snai2, which is induced by canonical Wnt signaling to be expressed in the early CNC, is pivotal for CNC induction and migration in Xenopus. However, snai2 expression is silenced during CNC migration, and its roles at later developmental stages remain unclear. We generated a transgenic X. tropicalis line that expresses enhanced green fuorescent protein (eGFP) driven by the snai2 promoter/enhancer, and observed eGFP expression not only in the pre-migratory and migrating CNC, but also the diferentiating CNC. This transgenic line can be used directly to detect defciencies in CNC development at various stages, including subtle perturbation of CNC diferentiation. In situ hybridization and immunohistochemistry confrm that Snai2 is re-expressed in the diferentiating CNC. Using a separate transgenic Wnt reporter line, we show that canonical Wnt signaling is also active in the diferentiating CNC. Blocking Wnt signaling shortly after CNC migration causes reduced snai2 expression and impaired diferentiation of CNC-derived head cartilage structures. These results suggest that Wnt signaling is required for snai2 reexpression and CNC diferentiation