Molecular Genetics of Drosophila Neurogenesis

The central nervous system in Drosophila is derived from a set of embryonic precursor cells called neuroblasts. Morphogenetic movements are initiated immediately after blastoderm formation, resulting in the establishment of the ectodermal and endodermal germ layers. Subsequently, the morphologically homogeneous ectodermal layer exhibits the first visible signs of differentiation (Poulson 1950; Hartenstein and Campos-Ortega 1984). The region of the ectoderm below the mesoderm and lying symmetrically on both sides of the ventral midline consists of approximately 1600 cells and is designated the neurogenic region. As development proceeds, cells within this medial ectodermal region uniformly increase in size, rendering them morphologically distinct from the remainder of the ectodermal cells (Hartenstein and Campos-Ortega 1984). About one-fourth of the cells in the neurogenic region then segregate toward the interior of the embryo. These cells are the neuroblasts, and will eventually give rise to the central nervous system. The rest of the cells, designated...