A variety of additional MF bundling or linking proteins have been described in the nervous system. For example, fimbrin may play a role in the formation of MF bundles in growth cone filopodia. Still other actin-binding proteins may regulate MF assembly [22,23]. Gelsolin fragments MFs in a Ca2+-sensitive manner but also caps and nucleates MFs. In contrast, profilin and β-thymosins bind to actin monomers and may act in part by sequestering actin subunits, although this oversimplifies the effects of these proteins. The list of MF-associated proteins has become quite long, and this diversity reflects the many forms of MF-based cytoskeletal structures.