Compartments and their boundaries in vertebrate brain development

Fifteen years ago, cell lineage restriction boundaries were discovered in the embryonic vertebrate hindbrain, subdividing it into a series of cell- tight compartments ( known as rhombomeres). Compartition, together with segmentally reiterative neuronal architecture and the nested expression of Hox genes, indicates that the hindbrain has a truly metameric organization. This finding initiated a search for compartments in other regions of the developing brain. The results of recent studies have clarified where compartment boundaries exist, have shed light on molecular mechanisms that underlie their formation and have revealed an important function of these boundaries: the positioning and stabilization of local signalling centres.