Actin-binding protein involved in motile and morphological processes. Inhibits actin polymerization, likely by sequestering G-actin. By capping the barbed ends of filaments, it also regulates motility. Seems to play an important role in clathrin-mediated endocytosis and distribution of endocytic organelles. May play a role in regulating the mature length of the middle and short rows of stereocilia. Interacts with G-actin; ADP-actin form and capping protein (CP). Isoform 2 interacts (via its N-terminal ADF-H domain) with G-actin (ADP-bound form) with significantly higher affinity than isoform 1. May also be able to interact with TWF1 and phosphoinositides, PI(4,5)P2. When bound to PI(4,5)P2, it is down-regulated. Interacts with MYO7A. Perinuclear and G-actin-rich cortical actin structure sublocalization. Isoform 2 found also along myofibrils in cardiomyocytes (PubMed:18837697). Localized in cochlea hair cells to the tips of the middle and short rows of stereocilia (PubMed:19955359). Isoform 1 is ubiquitously expressed (at protein level). Isoform 2 expression is restricted to heart and skeletal muscle where it is the predominant form. Expression was relatively weak during all of the embryonic stages. At 14.5 dpc, a slight increase in the expression could be observed in heart, CNS, and PNS. At 18.5 dpc, it is strongly expressed in the inner ear, hair cells and in the head muscles. No expression is detected in the nasal epithelium or in the skin keratinocytes. Phosphorylated on both serine/threonine and tyrosine. Mice lacking isoform 1 develop normally to adulthood, are fertile, and do not exhibit obvious morphological or behavioral abnormalities. Belongs to the actin-binding proteins ADF family. Twinfilin subfamily. Molecular embrace - Issue 73 of August 2006