TALEN-mediated mutagenesis in zebrafish reveals a role for r-spondin 2 in fin ray and vertebral development

R-spondin (Rspo) encodes a multi-domain protein that modulates the Wnt-signaling pathway. Two distinct rspo2 zebrafish mutants were generated by TALEN-mediated mutagenesis: a null mutant, rspo2^null, lacking all functional domains, and a hypomorphic mutant, rspo2^tsp, lacking the two N-terminal domains. Mutants were analyzed mainly for abnormalities in the skeletal system. Fin ray skeletons were formed normally in the rspo2^tsp mutants, but were absent from the rspo2^null mutants. Hypoplasia of the neural/hemal arches and ribs was observed in both mutants. Thus, the two rspo2 mutants help to identify the functions of Rspo2 in skeletogenesis, as well as functional differences among multiple Rspo2 domains.