Gliotactin, a novel transmembrane protein on peripheral glia, is required to form the blood-nerve barrier in Drosophila.

Peripheral glia help ensure that motor and sensory axons are bathed in the appropriate ionic and biochemical environment. In Drosophila, peripheral glia help shield these axons against the high K+ concentration of the hemolymph, which would largely abolish their excitability. Here, we describe the molecular genetic analysis of gliotactin, a novel transmembrane protein that is transiently expressed on peripheral glia and that is required for the formation of the peripheral blood-nerve barrier. In gliotactin mutant embryos, the peripheral glia develop normally in many respects, except that ultrastructurally and physiologically they do not form a complete blood-nerve barrier. As a result, peripheral motor axons are exposed to the high K+ hemolymph, action potentials fail to propagate, and the embryos are nearly paralyzed.