GLIAL DEVELOPMENT IN THE DROSOPHILA CNS REQUIRES CONCOMITANT ACTIVATION OF GLIAL AND REPRESSION OF NEURONAL DIFFERENTIATION GENES

Two classes of glial cells are found in the embryonic Drosophila CNS, midline glial cells and lateral glial cells. Midline glial development is triggered by EGF-receptor signalling, whereas lateral glial develo pment is controlled by the gem gene. Subsequent glial cell differentia tion depends partly on the pointed gene. Here we describe a novel comp onent required for all CNS glia development. The tramtrack gene encode s two zinc-finger proteins, one of which, ttkp69, is expressed in all non-neuronal CNS cells. We show that ttkp69 is downstream of gcm and c an repress neuronal differentiation. Double mutant analysis and coexpr ession experiments indicate that glial cell differentiation may depend on a dual process, requiring the activation of glial differentiation by pointed and the concomitant repression of neuronal development by t ramtrack.