MIGRATION OF GLIAL-CELLS INTO RETINAL AXON TARGET FIELD IN DROSOPHILA-MELANOGASTER

During the development of the Drosophila visual system, photoreceptor (retinal) axons (R axons) project retinotopically to their targets in the optic lobes, The establishment of this precise pattern of connecti ons does not depend on interactions between adjacent axon bundles, sug gesting that R axons rely on environmental signals for proper pathfind ing, Glial cells that are located along the R-axon trajectory are like ly candidates to provide guidance cues for R-axon navigation. This stu dy defines the origin of lamina glia (L glia), and demonstrates that L glia migrate into the lamina over a considerable distance, Glia are l ocated in positions at which the R axons make critical growth choices, In the absence of cues from the eye, several classes of glia migrate to their final positions within the optic lobe anlage and begin to dif ferentiate, Our results are consistent with a role for the glia in pro viding guidance cues to the R axons. (C) 1996 John Wiley & Sons, Inc.