Our objective is to describe and critique some of the experimental embryo-logical preparations used to analyze tissue interactions involved in neural induction in amphibians. The molecular basis of neural induction and the tissue interactions that carry the inductive signals are areas of active research, stimulated by the recent identification of several potential neural inducers (16), availability of regional molecular markers easily visualized with a good whole-mount RNA in situ hybridization method (7), and the work on Hox genes that may have a role in specifying regional differentiation of the vertebrate nervous system (8). These advances demand more of and make more useful the classical embryological manipulations used to characterize the tissue interactions involved in neural induction.
We will first describe the location and movements of the inducing and induced tissues, since misunderstanding of these aspects remains the major source of confusion in experimental design and interpretation in this area of research. Then we will describe several classical embryological methods that have been useful to us and to others in studying neural induction and development, pointing out the problems, difficulties, and liabilities of each of these methods.
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