@ Lehrstuhl für Entwicklungsbiologie VI, Universität Regensburg, 93040 Regensburg, Germany, § Department of Biology 156-29, California Institute of Technology, Pasadena, CA 91125, # TIFR, 560012 Bangalore, India,
To understand basic mechanisms of neurodegeneration we are investigating mutants showing general neurodegeneration in the central nervous system of the adult fly. drop-dead (drd) mutant flies die a few days after eclosion. Shortly before dying, they show behavioral abnormalities and brain sections from these flies reveal massive degeneration in all brain regions. EM studies on newly eclosed flies, which behave normally and do not reveal defects on the light microscopic level, show immature glial cells with shortened processes (Buchanan and Benzer, 1993). In slightly older flies, individual glial cells undergo apoptotic cell death. As a result, neurons as well as tracheal cells in the brain and thoracic ganglion lack complete glial wrapping, associated with subsequent degeneration. Cloning and sequencing of the gene predicts a novel protein of 825 amino acids, with multiple transmembrane regions. In-situ hybridization and immunohistochemistry reveal an expression of the drd transcript and protein in glia surrounding the neuropil of the optic lobes and central brain, and in glial cells associated with fiber tracts (the so-called sheath glia that give rise to multilayered wrappings reminiscent of vertebrate Schwann cells) and in the retina. Crossreactivity of an antibody raised against DRD reveals a conserved expression pattern in other insects and even staining in chick brains, persumably in glial endfeet. Swiss cheese (sws) mutant flies also show massive degeneration of the brain and reduced life span. EM studies reveal an opposite phenotype to the drd defect, namely “hyper-layered” glial wrappings. These defects are first detectable in the late pupa and increase with age. In addition we find an increase in the number of cells undergoing apoptosis with aging. In-situ hybridization shows expression of mRNA in most or all neurons of the central brain and thoracic ganglion of the adult. The sws transcript encodes a 1142 amino acid protein that shows sidnificant homology to human, yeast and C. elegans proteins of yet unknown functions and to the regulatory subunit of cAMP dependent protein kinase. One of the mutant alleles has a single amino acid substitution in this region similar to protein kinase A, a second one a substitution in a highly conserved stretch of glycines. Through the analysis of such mutants we hope to obtain insight into the role of glia in maintenance of neuronal systems, and the factors needed to prevent neurodegeneration.