CNS MIDLINE CELLS IN DROSOPHILA INDUCE THE DIFFERENTIATION OF LATERALNEURAL CELLS

Cells located at the midline of the developing central nervous system perform a number of conserved functions during the establishment of th e lateral CNS. The midline cells of the Drosophila CNS were previously shown to be required for correct pattern formation in the ventral ect oderm and for the induction of specific mesodermal cells. Here we inve stigated whether the midline cells are required for the correct develo pment of lateral CNS cells as well. Embryos that lack midline cells th rough genetic ablation show a 15% reduction in the number of cortical CNS cells. A similar thinning of the ventral nerve cord can be observe d following mechanical ablation of the midline cells. We have identifi ed a number of specific neuronal and glial cell markers that are reduc ed in CNS midline-less embryos (in single-minded embryos, in early hea t-shocked Notch(ts1) embryos or in embryos where we mechanically ablat ed the midline cells). Genetic data suggest that both neuronal and gli al midline cell lineages are required for differentiation of lateral C NS cells. We could rescue the lateral CNS phenotype of single-minded m utant embryos by transplantation of midline cells as well as by homoto pic expression of single-minded, the master gene for midline developme nt. Furthermore, ectopic midline cells are able to induce enhanced exp ression of some lateral CNS cell markers, We thus conclude that the CN S midline plays an important role in the differentiation or maintenanc e of the lateral CNS cortex.