Stabilizing the regionalisation of the developing vertebrate central nervous system

During embryonic development, a number of tissues are patterned by their subdivision into domains with distinct regional identity. An important question is how sharp interfaces are established and maintained between adjacent domains despite the potential for scrambling due to cell intermingling during tissue growth. Two mechanisms have been found to underlie the maintenance of sharp interfaces: the specific restriction of cell mixing across boundaries, or the switching of identity of cells that cross between domains. We review the evidence for these mechanisms at distinct boundaries in the developing vertebrate central nervous system, and discuss what is known about their molecular mediators. (C) 2002 Wiley Periodicals, Inc.