Our understanding of the molecular mechanisms involved in mammalian brain development remains limited. However, the last few years have wit nessed a quantum leap in our knowledge, due to technological improve ments, particularly in molecular genetics. Despite this progress, the available body of data remains mostly phenomenological and reveals very little about the grammar that organizes the molecular dictionary to articulate a pheno type. Nevertheless, the recent progress in genetics will allow us to contem plate, for the first time, the integration of observation into a coherent view of brain development. Clearly, this may be a major challenge for the next century, and arguably is the most important task of contemporary develop mental biology. The purpose of the present book is to provide an overview that syn thesizes up-to-date information on selected aspects of mouse brain devel opment. Given the format, it was not possible to cover all aspects of brain development, and many important subjects are missing. The selected themes are, to a certain extent, subjective and reflect the interests of the contributing authors. Examples of major themes that are not covered are peripheral nervous system development, including myelination, the development of the hippocampus and several other CNS structures, as well as the developmental function of some important morphoregulatory molecules."

Only five years ago, nobody in his right mind would have consid ered publishing a book on reeler as a model for brain develop ment. Although this interesting mutation has been with us for half a century, it is fair to say that, in spite of a wave of enthusiasm in the late sixties and early seventies, generated primarily by Sidman, Caviness and colleagues, studies of reeler mice fell pro gressively out of fashion during the next two decades. All that changed almost overnight when the cloning of the reeler gene, dubbed reelin, was reported in Tom Curran's laboratory in 1995. The fact that the same gene was identified at the same time independently by two other groups using positional cloning sug gested strongly that reelin was the right candidate. Although the key experiments of transgenic rescue have not been made (and perhaps will never be), the equation "reeler is reelin" has been established beyond reasonable doubt, as alterations of the reelin gene and/or its expression have been found in at least five alleles of reeler and in the mutation Shaking Rat Kawasaki (SRK), an ortholog of reeler."