At the nexus between pattern formation and cell-type specification: the generation of individual neuroblast fates in the Drosophila embryonic centralnervous system

The specification of specific and often unique fates to individual cells as a function of their position within a developing organism is a fundamental process during the development of multicellular organisms. The development of the Drosophila embryonic central nervous system serves as an excellent model system in which to clarify the developmental mechanisms that link pat tern formation to cell-type specification. The Drosophila embryonic central nervous system develops from a set of neural stem cells termed neuroblasts . Neuroblasts arise from the ectoderm in an invariant pattern, and each neu roblast acquires a unique fate based on its position within this pattern. T wo groups of genes recently have been demonstrated to govern the individual fate specification of neuroblasts. One group, the segment polarity genes, enables neuroblasts that develop in different anteroposterior positions to acquire different fates. The second group, referred to as the columnar gene s, ensures that neuroblasts that develop in different dorsoventral domains assume different fates. When integrated, the activities of the segment pola rity and columnar genes create a Cartesian coordinate system that bestows u nique fates to individual neuroblasts as a function of their position of fo rmation within the ectoderm. BioEssays 1999;21:922-931. (C) 1999 John Wiley & Sons, Inc.