Phagocytic glial cells: sculpting synaptic circuits in the developing nervous system

- Glia play actives roles in activity-dependent synaptic pruning.
- Phagocytosis is a common mechanism by which glia eliminate developing synapses.
- Schwann cells are involved in axonal pruning at the developing mammalian NMJ.
- Drosophila glial cells are involved in axonal pruning at the NMJ and mushroom body.
- Microglia play key roles in local synaptic circuit pruning in the mammalian CNS.

In the developing nervous system, synaptic connections are formed in excess and must remodel to achieve the precise synaptic connectivity characteristic of the mature organism. Synaptic pruning is a developmental process in which subsets of synapses are eliminated while the remaining synapses are preserved and strengthened. Recent findings have demonstrated unexpected roles for glial cells in this developmental process. These data demonstrate that phagocytic glia engulf synaptic and/or axonal elements in the developing nervous system and disruptions in this process result in sustained deficits in synaptic connectivity. These new findings highlight the importance of glia for nervous system development and function and may shed new light on mechanisms underlying nervous system disease.