Profilin 1 is a ubiquitous actin monomer-binding protein involved in actin polymerization in response to extracellular signals. Three profilin genes have been identified: profilin 1, 2, and 3. Profilin 1 is the most ubiquitous and abundant, and is highly expressed throughout development and adulthood inmost tissues including brain. Profilin 2 is the neuronal specific isoform and profilin 3 is a testis specific isoform. Profilins of eukaryotic cells are small (12-15 kDa) cytoplasmic proteins that bind to actin monomers, polyphosphoinositides and polymers of L-proline. Profilins were shown to be important for normal cell proliferation, differentiation and motility. Deletion of profilin 1 gene leads to an embryonic lethal phenotype.