Drebrin (developmentally-regulated brain protein) is a major neuronal F-actin binding protein involved in the control of actin dynamics and neuronal morphogenesis. Three major isoforms of drebrin, resulting from alternative splicing of a single gene, have been identified in the brain: the embryonic isoforms designated E1 and E2 and the adult or A isoform (95-120 kDa). An additional truncated form of drebrin A, s-drebrin/A2 (42 kDa), is specifically expressed in the adult brain, but not in non-neuronal tissues. Drebrin is also widely expressed in a variety of cells including epithelial, endothelial, and smooth muscle cells and is associated at cell-cell adhering junction sites. Drebrin is thought to play a central role in the formation of axons and dendrites during neuronal development and in neuronal plasticity in the adult brain. The expression of each drebrin isoform is regulated throughout distinct phases in neuronal development. The earliest embryonic form E1, is thought to function in migration, while the E2 isoform, which replaces E1 during embryogenesis, is believed to play a role in migration as well as formation of axons and dendrites. Drebrin E2 is present at low levels in the adult brain. The drebrin A isoform, which is only present in mature neurons, is assumed to be involved in synaptic plasticity. Drebrin E2 and A isoforms are targeted to different regions of actin localization. In neurons, the E2 isoform localizes to the submembrane region, while the A isoform is specifically located and evenly distributed throughout the post-synaptic dendritic spine.