EMBRYONIC-DEVELOPMENT OF THE DROSOPHILA BRAIN - II - PATTERN OF GLIAL-CELLS

Glial cells in Drosophila and other insects are organized in an outer layer that envelops the surface of the central and peripheral nervous system (subperineurial glia, peripheral glia), a middle layer associat ed with neuronal somata in the cortex (cell body glia), and an inner l ayer surrounding the neuropile (longitudinal glia, midline glia, nerve root glia). In the ventral nerve cord, most glial cells are formed by a relatively small number of neuro-glioblasts; subsequently, glial ce ll precursors migrate and spread out widely to reach their final desti nation. By using a glia-specific marker (antibody against the Repo pro tein) we have reconstructed the pattern of glial cell precursors at su ccessive developmental stages, focusing on the glia of the supraesopha geal ganglion and subesophageal ganglion which are not described in pr evious studies. Digitized images of consecutive optical sections were used to generate 3-D models that show the spatial pattern of glial cel l precursors in relationship to the neuropile, brain surface, and peri pheral nerves. Similar to their spatial organization in the ventral ne rve cord, glial cells of the brain populate the brain nerves and outer surface, cortical cell body layer, and cortex-neuropile interface. Ne uropile-associated glial cells arise from a cluster located at the bas e of the supraesophageal ganglion; from this position, they migrate do rsally along the developing axon tracts and by late embryonic stages f orm a sheath around all neuropile compartments, including the supraeso phageal commissure. Surface and cell body glial cells derive from seve ral discrete foci, notably two large clusters at the deuterocerebrum/p rotocerebrum boundary and the posterior protocerebrum From these foci, glial cells then fan out to envelop the surface of the supraesophagea l ganglion. J. Comp. Neurol. 402:32-47, 1998. (C) 1998 Wiley-Liss, Inc .