Constructing by Disposing: Regulation of Neuronal Morphogenesis by Phagocytosis

Excerpt

The construction of a functional nervous system involves not only the addition of new neurites or synapses but also the elimination of excessive or temporary structures. Being responsible for the trimming work, diverse phagocytes engulf apoptotic neurons, dissolve large pieces of axons or dendrites, or nibble away specific synapses. In these processes, phagocytes do not merely clean up the mess resulting from neuronal destruction. Instead, they are often responsible for killing the neurons or dismantling the excessive neurites/synapses. Thus, failure of phagocytosis can result in defects in neuronal morphology and connectivity. Phagocytosis of neurons is triggered by “eat-me” signals exposed on the neuronal surface. Engulfment receptors on phagocytes recognize these signals and promote cytoskeletal and transcriptional changes necessary for phagocytosis and other responses. Here, we review the experimental systems used to study phagocytosis during neuronal remodeling in both invertebrates and vertebrates and recent progress that sheds light on the molecular pathways underlying phagocytosis in the developing nervous system.