Overexpression of drebrin A in immature neurons induces the accumulation of F-actin and PSD-95 into dendritic filopodia, and the formation of large abnormal protrusions.

Drebrin A is a neuron-specific F-actin binding protein, and plays a pivotal role in the spine formation. In this study, we expressed drebrin A tagged with green fluorescent protein (GFP-DA) in hippocampal neurons at 7-9 days in vitro when presynaptic terminals are not fully maturated. GFP-DA was accumulated in dendritic protrusions and formed large abnormal structures. Since these structures were similar to filopodia in terms of lack of MAP2 immunostaining, we named them "megapodia" meaning large dendritic filopodia. F-actin and PSD-95 were also accumulated in megapodia, and their amounts were significantly correlated with that of GFP-DA. However, the expression of GFP-DA did not result in the promotion of the morphological change from filopodia into spines. These results demonstrate that drebrin A accumulates spine-resident proteins via protein-protein interaction in filopodia, and suggest that the spine formation requires the concurrence of the increase of drebrin-A expression and the functional presynaptic contact.