THE HOMEOBOX GENE REPO IS REQUIRED FOR THE DIFFERENTIATION AND MAINTENANCE OF GLIA FUNCTION IN THE EMBRYONIC NERVOUS-SYSTEM OF DROSOPHILA-MELANOGASTER

We describe the cloning, expression and phenotypic characterisation of repo, a gene from Drosophila melanogaster that is essential for the d ifferentiation and maintenance of glia function. It is not, however, r equired for the initial determination of glial cells. In the embryo, t he gene, which encodes a homeodomain protein, is expressed exclusively in all developing glia and closely related cells in both the central and peripheral nervous systems. The only observed exceptions in the CN S are the midline glia derived from the mesectoderm and two of three s egmental nerve root glial cells. Using a polyclonal antibody we traced the spatial and temporal pattern of the protein expression in detail. Embryos homozygous for null alleles of the protein exhibit late devel opmental defects in the nervous system, including a reduction in the n umber of glial cells, disrupted fasciculation of axons, and the inhibi tion of ventral nerve cord condensation. The expression of an early gl ial-specific marker is unaffected in such homozygotes. By contrast, th e expression of late glial-specific markers is either substantially re duced or absent. The specificity of expression is also observed in the locust Schistocerca gregaria and is thus evolutionarily conserved.