Abstract
The analysis of hereditary neuro-muscular diseases in the mouse and in other vertebrates may contribute to our understanding of the developmental interactions between spinal cord and sceletal muscle. Meaningful biochemical analysis must be preceded by “biological mixing experiments” to demonstrate whether a given mutation is cell-autonomous, and, if so, which cell type caries the primary defect. Techniques are available to carry out the critical experiment in vivo (artificial chimaeras) or in culture.