Recent data from cultured epithelial cells and fibroblasts shows that the actin binding protein coronin has a central role in defining the morphology of actin-based protrusions. Coronin can modify the F-actin branches generated by the Arp2/3 complex. Current evidence suggests that coronin enhances cytoskeletal flexibility (since coronin-associated branches are not restricted to the 70° angle characteristic of Arp2/3-associated branches). Coronin also modulates activity of the phosphatase Slingshot, which activates the actin-depolymerizing protein cofilin. These data suggest that coronin may play an important role in the regulation of the actin network required for activity-dependent spine-plasticity. Using immuno-electron microscopy, we found that coronin concentrates in dendritic spines in hippocampus, and it is especially abundant in large spines with perforated postsynaptic densities with a mushroom morphology, likely to reflect different activation states. Notwithstanding spine heterogeneity, considerable evidence suggests that the functionally most important variable is spine size itself: within CA1 hippocampus, spine volume is closely related to the number of presynaptic neurotransmitter vesicles, to the length of the synaptic apposition, to the number of postsynaptic AMPA receptors, and to the size of the unitary EPSC. The fact, that larger spines contain higher levels of coronin suggests, that coronin might play a pivotal role in activity-dependent spine plasticity that is believed to underlie learning and memory.

This work was supported by OTKA (grant# K83830) and by the János Bólyai Reseach fellowship (to Bence Rácz) of the Hungarian Academy of Sciences.