The identification of the cardiac neural crest and its role in the premature death (p) mutation in Ambystoma mexicanum.

Abstract

Little is known as to the location of the cardiac neural crest and its contribution to cardiovascular system in the developing amphibian embryo. I have attempted to identify and define the boundaries of the cardiac neural crest in the neurula stage wild type axolotl (Ambystoma mexicanum) embryo by labelling the cardiac neural crest cells with the fluorescent lineage label, DiI. Cardiac neural crest cells were found to be located posterior to the hindbrain region of the neural folds, and above the first two somites, before migrating ventrally to provide ectomesenchymal support in the anterior outflow portion of the heart. My results indicate that the role and location of the cardiac neural crest in the axolotl are similar to the role and location of the cardiac crest in other vertebrates. I also labelled other regions of the cranial neural fold in the stage 20 axolotl embryo. I constructed a fate map of the cranial neural folds in the late neurula stage embryo. Anterior neural fold cells contributed to the anterior structures of the brain and visceral skeleton, while more caudally located neural fold cells formed more posterior structures. My fate map corresponded to those previously constructed at earlier stages in neurulation. I have also examined the development of the cardiac neural crest in axolotl embryos exhibiting the premature death (p) mutation. I examined $(p/p)$ mutants with DiI-labelling. Any deleterious effects of the premature death mutation were not detectable in cardiac neural crest. However, the migration and specification of the cranial neural crest involved in gill formation was noticeably hindered, thus substantiating that certain neural crest cells in the mutant fail to respond to inductive signals. (Abstract shortened by UMI.)