loco encodes an RGS protein required for Drosophila glial differentiation

In Drosophila, glial cell development depends on the gene glial cells missi ng (gcm), gem activates the expression of other transcription factors such as POINTED and REPO, which control subsequent glial differentiation. In ord er to better understand glial cell differentiation, we have screened for ge nes whose expression in glial cells depends on the activity of POINTED. Usi ng an enhancer trap approach, we have identified loco as such a gene. loco is expressed in most lateral CNS glial cells throughout development. Embryo s lacking loco function have an normal overall morphology, but fail to hatc h. Ultrastructural analysis of homozygous mutant loco embryos reveals a sev ere glial cell differentiation defect. Mutant glial cells fail to properly ensheath longitudinal axon tracts and do not form the normal glial-glial ce ll contacts, resulting in a disruption of the blood-brain barrier. Hypomorp hic loco alleles were isolated following an EMS mutagenesis. Rare escapers eclose which show impaired locomotor capabilities, loco encodes the first t wo known Drosophila members of the family of Regulators of G-protein signal ling (RGS) proteins, known to interact with the a subunits of G-proteins, L OCO specifically interacts with the Drosophila G alpha i-subunit. Strikingl y, the interaction is not confined to the RGS domain. This interaction and the coexpression of LOGO and G alpha i suggests a function of G-protein sig nalling for glial cell development.