phospholipase C, beta 3 is required for Endothelin1 regulation of pharyngeal arch patterning in zebrafish

Genetic and pharmacological studies demonstrate that Endothelin1 (Edn1) is a key signaling molecule for patterning the facial skeleton in fish, chicks, and mice. When Edn1 function is reduced early in development the ventral lower jaw and supporting structures are reduced in size and often fused to their dorsal upper jaw counterparts. We show that schmerle (she) encodes a zebrafish ortholog of Phospholipase C, beta 3 (Plcβ3) required in cranial neural crest cells for Edn1 regulation of pharyngeal arch patterning. Sequencing and co-segregation demonstrates that two independent she (plcβ3) alleles have missense mutations in conserved residues within the catalytic domains of Plcβ3. Homozygous plcβ3 mutants are phenotypically similar to edn1 mutants and exhibit a strong arch expression defect in Edn1-dependent Distalless (Dlx) genes as well as expression defects in several Edn1-dependent intermediate and ventral arch domain transcription factors. plcβ3 also genetically interacts with edn1, supporting a model in which Edn1 signals through a G protein-coupled receptor to activate Plcβ3. Mild skeletal defects occur in plcβ3 heterozygotes, showing the plcβ3 mutations are partially dominant. Through a morpholino-mediated deletion in the N-terminal PH domain of Plcβ3, we observe a partial rescue of facial skeletal defects in homozygous plcβ3 mutants, supporting a hypothesis that an intact PH domain is necessary for the partial dominance we observe. In addition, through mosaic analyses, we show that wild-type neural crest cells can efficiently rescue facial skeletal defects in homozygous plcβ3 mutants, demonstrating that Plcβ3 function is required in neural crest cells and not other cell types to pattern the facial skeleton.