Figure 2. Models of cargo transport into dendritic spines.

(A). A diffusive model where CaMKII could phosphorylate kinesin and/or adapter proteins in the dendrite shaft, releasing cargo (a vesicle in these models) to diffuse freely in the dendritic shaft or into the spine head. (B) A hand-off-model, where myosin and kinesin are bound to the same vesicle. CaMKII could phosphorylate kinesin and/or adapters releasing the vesicle from MTs. The vesicle then attaches to actin filaments in the dendrite shaft or spine neck and is transported into the spine head via myosin-driven transport. (C) A direct-deposit model where microtubules can polymerize into the spine head and kinesin can directly traffic vesicles into the spine where CaMKII and Ca²⁺ concentrations are the highest. Note that a hand-off to actin could also occur in the spine head in this model. (D) Flow diagram of the CaMKII pathway leading to microtubule invasion of spines and cargo unloading in dendritic spines.