Figure 3.

Synapse formation between dendrites and axons in the presence (A) and absence of Arp2/3 (B, C). (A) Dendritic spine with a mature-type morphology supported by actin cytoskeleton meshwork. Presynaptic axon is in contact with the dendritic spine. Postsynaptic receptors are supported by actin cytoskeleton on the plasma membrane. (B) Lack of dendritic spines in the absence of Arp2/3 complex. Presynaptic axon is in direct contact with the dendritic shaft. (C) Immature dendritic spines supported by filopodia-like protrusions with non-branching actin filaments in the absence of Arp2/3 complex lead to anomalous formation of double-axonal synapses. This figure is modified from Figure 4 in Ref. 24.