Institut für Genetik, Universität Mainz, Saarstraße 21, D-55122 Mainz,
CNS development in Drosophila starts with the delamination from the neuroectoderm of 30 neuroblasts (NBs) per truncal hemisegment, which in the embryo give rise to about 350 neuronal and 30 glial progeny cells. The mechanisms controlling the specification of the individual NBs and the differentiation of their specific lineages are unknown. By labelling individual neuroectodermal cells with the fluorescent tracer DiI we have clarified the entire embryonic lineages of the mesectodermal midline progenitors (1) and of most of the NBs (2). 10% of the glial cells derive from medial NBs, 90% from lateral NBs, which produce glia exclusively or glia in addition to neurons (see abstract of Rickert et al.). The identified wildtype CNS lineages provide a foundation for the interpretation of genetic and experimental pertubations.
The homeodomain protein Repo is expressed in all glial cells except those derived from the ventral midline. repo mutants lack about 50% of the glia (3). We show on the level of individual cell lineages that in the mutant partial loss of glial cells is accompanied by specific axonal misguidance, failure of neuronal movements and proceeding neuronal cell-death. The glial cells first arise but fail to differentiate and are finally pushed out of the nerve cord where they are phagocytosed. In some cases we find macrophages even within the nerve cord from where they are usually excluded. On the molecular level we have cloned and sequenced the repo gene of Drosophila virilis to determine which parts of the protein are highly conserved compared to Drosophila melanogaster. This will give us an idea about the functional important domains of the protein beside the homeodomain.
(1) Bossing, T. and Technau, G.M. (1994), Development 120, 1895-1906. (2) Bossing, T., Udolph, G., Doe, C.Q., and Technau, G.M., Devl. Biol., in press. (3) Halter, D., Urban, J., Rickert, C., Ner, S., Ito, K., Travers, A. and Technau, G.M. (1995), Development 121, 317-332.
Supported by the DFG (Te 130/4-3)