GLIAL-CELLS MISSING - A BINARY SWITCH BETWEEN NEURONAL AND GLIAL DETERMINATION IN DROSOPHILA

In the Drosophila CNS, both neurons and glia are derived from neurobla sts. We have identified a gene, glial cells missing (gcm), that encode s a novel nuclear protein expressed transiently in early glial cells. Its mutation causes presumptive glial cells to differentiate into neur ons, whereas its ectopic expression forces virtually all CNS cells to become glial cells. Thus, gem functions as a binary switch that turns on glial fate while inhibiting default neuronal fate of the neuroblast s and their progeny. Similar results are also obtained in the PNS. Ana lyses of the mutant revealed that ''pioneer neurons'' can find correct pathways without glial cells and that neurons and glia have a common molecular basis for individual identity.