Experimentally provoked neural induction results in an incomplete expression of neuronal traits

In the amphibian embryo, the ectoderm becomes a neural structure during gastrulation as a result of an interaction with the dorsal mesoderm. From that time onward, neurectodermal cells have the ability to express in vitro a large variety of mature phenotypes without further interaction with the inducing tissue. The neuralization of the ectoderm can be reproduced in a variety of experimental situations that do not involve the dorsal mesoderm. In this study we have analyzed biochemically the extent to which artificial inductions mimic the natural inducing process. Making use of antibodies specific to different neurotransmitter pathways, we have shown that the repertoire of the phenotypes expressed by experimentally induced neurons is always restricted compared to those obtained after induction in vivo. Only a limited number of generic neuronal characteristics are expressed. These results suggest that the expression of a complete neuronal phenotype normally involves a sequence of inductive events that can be experimentally uncoupled.