RK2, A GLIAL-SPECIFIC HOMEODOMAIN PROTEIN REQUIRED FOR EMBRYONIC NERVE CARD CONDENSATION AND VIABILITY IN DROSOPHILA

We report the identification of RK2, a glial-specific homeodomain prot ein. RK2 is localized to the nucleus of virtually all embryonic and im aginal glial cells, with the exception of midline glia. Embryos mutant for the gene encoding RK2 are embryonic lethal but normal for early g liogenesis (birth, initial divisions and migration of glia) and axonog enesis (neuronal pathfinding and fasciculation). However, later in dev elopment, there are significantly fewer longitudinal glia that are spa tially disorganized; in addition, there is a slight disorganization of axon fascicles and a defective nerve cord condensation. This suggests that RK2 is not required for early glial determination, but rather fo r aspects of glial differentiation or function that are required for e mbryonic viability.