Potential role of synaptopodin in spine motility by coupling actin to the spine apparatus.

Dendritic spines are dynamic structures that rapidly remodel their shape and size. These morphological adaptations are regulated by changes in synaptic activity, and result from rearrangements of the postsynaptic cytoskeleton. A cytoskeletal molecule preferentially found in mature spines is the actin-associated protein synaptopodin. It is strongly expressed by spine-bearing neurons in the olfactory bulb, striatum, cerebral cortex, and hippocampus. In the hippocampus, principal cells express synaptopodin mRNA and sort the protein to the spine compartment. Within the spine microdomain, synaptopodin is preferentially located in the spine neck and is closely associated with the spine apparatus. On the basis of these data we hypothesize that synaptopodin could affect spine motility by bundling actin filaments in the spine neck. In addition, it could link the actin cytoskeleton of spines to intracellular calcium stores, i.e., the spine apparatus and the smooth endoplasmic reticulum.