By Kohei Hatta, Andreas W. Püschel* and Charles B. Kimmel
Institute of Neuroscience, University of Oregon, Eugene, Oregon 97403, USA; * MPI für Hirnforschung, Abt. Neurochemie, Deutschorden str. 46, D-6000 Frankfurt a.M. 71, GERMANY
In all vertebrates the brain develops from the enlarged anterior part of the neural plate. However, in the zebrafish mutant cyclops the girth of the central nervous system (CNS) is nearly uniform along its length. Changes in expression patterns of homeobox genes and neuronal markers reveal that the entire ventral forebrain is missing, as well as its precursor region in the neural plate. The massive deletion is due to a nonautonomous action of the mutation: as few as one wild-type cell transplanted to the midline of a mutant embryo, can rescue the forebrain phenotype including cyclopia. Establishment of forebrain ventral positional values and size may thus require inductive signaling by CNS midline cells of a "prefloor plate", whose specification depends upon the cyclops gene product.
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