Expression of five frizzleds during zebrafish craniofacial development.

Wnt/Planar Cell Polarity (PCP) signaling is critical for proper animal development. While initially identified in Drosophila, this pathway is also essential for the proper development of vertebrates. Zebrafish mutants, defective in the Wnt/PCP pathway, frequently display defects in convergence and extension gastrulation movements and additional later abnormalities including problems with craniofacial cartilage morphogenesis. Although multiple Frizzled (Fzd) homologues, Wnt receptors, were identified in zebrafish, it is unknown which Fzd plays a role in shaping the early larvae head skeleton. In an effort to determine which Frizzleds are involved in this process, we analyzed the expression of five zebrafish frizzled homologues fzd2, 6, 7a, 7b, and 8a from 2-4days post-fertilization (dpf). During the analyzed developmental time points fzd2 and fzd6 are broadly expressed throughout the head, while the expression of fzd7a, 7b and 8a is much more restricted. Closer examination revealed that fzd7b is expressed in the neural crest and the mesodermal core of the pharyngeal arches and in the chondrocytes of newly stacked craniofacial cartilage elements. However, fzd7a is only expressed in the neural crest of the pharyngeal arches and fzd8a is expressed in the pharyngeal endoderm.