CNS MIDLINE DEVELOPMENT IN DROSOPHILA

The first cells specified during CNS development of vertebrates and in vertebrates are the cells located at the midline of the neuroepitheliu m. In Drosophila the development of these cells requires inductive sig nals from the mesoderm. Later in CNS development, the midline cells ar e in turn influencing the flanking neuroectoderm, contributing to the establishment of dorsoventral positional information. During axonal pa ttern formation the midline cells are required in guiding commissural growth cones towards and across the midline. The midline consists of o nly few, easily identifiable neuronal and glial cells per segment. The development of midline glial cells is relatively well understood. The ir differentiation appears to be controlled by the concomitant express ion of two different sets of transcription factors. Activation of glia l differentiation mediated by the ETS transcription factor encoded by pointed (whose activity depends on EGF-receptor signalling) occurs in concert with repression of neuronal differentiation mediated by the Zn -finger transcription factor encoded by tramtrack.