Neural induction: toward a unifying mechanism.

Neural induction constitutes the initial step in the generation of the vertebrate nervous system. In attempting to understand the principles that underlie this process, two key issues need to be resolved. When is neural induction initiated, and what is the cellular source and molecular nature of the neural inducing signal(s)? Currently, these aspects of neural induction seem to be very different in amphibian and amniote embryos. Here we highlight the similarities and the differences, and we propose a possible unifying mechanism.