MACROPHAGES AND GLIA PARTICIPATE IN THE REMOVAL OF APOPTOTIC NEURONS FROM THE DROSOPHILA EMBRYONIC NERVOUS-SYSTEM

Cell death in the Drosophila embryonic central nervous system (CNS) pr oceeds by apoptosis, which is revealed ultrastructurally by nuclear co ndensation, shrinkage of cytoplasmic volume, and preservation of intra cellular organelles. Apoptotic cells do not accumulate in the CNS but are continuously removed and engulfed by phagocytic haemocytes. To det ermine whether embryonic glia can function as phagocytes, we studied s erial electron microscopic sections of the Drosophila CNS. Apoptotic c ells in the nervous system are engulfed by a variety of glia including midline glia, interface (or longitudinal tract) glia, and nerve root glia. However, the majority of apoptotic cells in the CNS are engulfed by subperineurial glia in a fashion similar to the microglia of the v ertebrate CNS. A close proximity between macrophages and subperineuria l glia suggests that glia may transfer apoptotic profiles to the macro phages. Embryos affected by the maternal-effect mutation Bicaudal-D ha ve no macrophages. In the absence of macrophages, most apoptotic cells are retained at the outer surfaces of the CNS, and subperineurial gli a contain an abundance of apoptotic cells. Some apoptotic cells are ex pelled from the CNS, which suggests that the removal of apoptotic cell s can occur in the absence of macrophages. The number of subperineuria l glia is unaffected by changes in the rate of neuronal apoptosis. (C) 1995 Wiley-Liss, Inc.