Bone morphogenetic protein-4 and Noggin signaling regulates pigment cell distribution in the axolotl trunk.

Wild-type (dark) and white mutant axolotl (Ambystoma mexicanum) embryos were used to investigate the role of the secreted growth factor bone morphogenetic protein-4 (BMP-4) and its antagonist, Noggin, in dorso-lateral trunk neural crest (NC) migration. Implantation of a BMP-4-coated microbead caused a melanophore-free zone around the bead, reduction of the dorsal fin above the bead, and disappearance of myotome tissue. We established a novel method that allows controlled induction of protein synthesis and release. Xenopus animal cap (XAC) cells injected with heat shock-inducible constructs for BMP-4 and Noggin were implanted into axolotl embryos and protein expression was induced at defined time points. With this approach, we could demonstrate for the first time that Noggin can stimulate melanophore migration in the white mutant. We further showed that implantation of BMP-4 expressing XAC cells alters pigment cell distribution without affecting muscle and dorsal fin development.