THE EMBRYONIC CENTRAL-NERVOUS-SYSTEM LINEAGES OF DROSOPHILA-MELANOGASTER .2. NEUROBLAST LINEAGES DERIVED FROM THE DORSAL PART OF THE NEUROECTODERM

In Drosophila, central nervous system (CNS) formation starts with the delamination from the neuroectoderm of about 30 neuroblasts (NBs) per hemisegment. They give rise to approximately 350 neurons and 30 glial cells during embryonic development. Understanding the mechanisms leadi ng to cell fate specification and differentiation in the CNS requires the identification of the NE lineages. The embryonic lineages derived from 17 NBs of the ventral part of the neuroectoderm have previously b een described (Bossing et al., 1996). Here we present 13 lineages deri ved from the dorsal part of the neuroectoderm and we assign 12 of them to identified NBs. Together, the 13 lineages comprise approximately 1 20 neurons and 22 to 27 glial cells which we include in a systematic t erminology. Therefore, NBs from the dorsal neuroectoderm produce about 90% of the glial cells in the embryonic ventral ganglion. Two of the NBs give rise to glial progeny exclusively (NB 6-4A, G;P) and five to glia as well as neurons (NBs 1-3, 2-5, 5-6, 6-4T, 7-4). These seven NB s are arranged as a group in the most lateral region of the NE layer. The other lineages (NBs 2-4, 3-3, 3-5, 4-3, 4-4, 5-4, clone y) are com posed exclusively of neurons (interneurons, motoneurons, or both). Add itionally, it has been possible to link the lateral cluster of even-sk ipped expressing cells (EL) to the lineage of NE 3-3. Along with the p reviously described clones, the vast majority (more than 90%) of cell lineages in the embryonic ventral nerve cord (thorax, abdomen) are now known. Moreover, previously identified neurons and most glial cells a re now Linked to certain lineages and, thus, to particular NBs. This c omplete set of data provides a foundation for the interpretation of mu tant phenotypes and for future investigations on cell fate specificati on and differentiation. (C) 1997 Academic Press.