The research in my lab is centered on the “espins,” a novel family of multifunctional actin-bundling proteins, and the elucidation of their roles in the organization and function of the actin cytoskeleton of hair cell stereocilia and sensory cell microvilli. Espins are produced in multiple isoforms from a single gene. They are present at high concentration in the parallel actin bundle of hair cell stereocilia and are the target of deafness mutations in mice and humans. For example, the jerker mutation in the espin gene of mice causes recessive hereditary deafness and vestibular dysfunction accompanied by an abnormal shortening of hair cell stereocilia. Espins are also present at high concentration in the microvilli of taste receptor cells, solitary chemoreceptor cells, vomeronasal sensory neurons and Merkel cells, suggesting that these proteins play important, general roles in the microvillar projections of vertebrate sensory cells. Unlike other actin-bundling proteins found in the microvilli and stereocilia of vertebrates, espins are potent actin-bundling proteins that are not inhibited by Ca2+. In cells, espins efficiently elongate parallel actin bundles and, thereby, help determine the steady-state length of microvilli and stereocilia. Espins bind actin monomer via their Wiskott-Aldrich Syndrome protein homology 2 (WH2) domain in vitro and in vivo andcan assemble actin bundles in cells. Certain espin isoforms can also bind phosphatidylinositol 4,5-bisphosphate, profilins or SH3 proteins. These biological activities distinguish espins from other actin-bundling proteins and may make them especially well-suited to sensory cells.