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Cover  This month's cover is an epifluorescence micrograph of a HeLa cell transiently transfected with GFP-bovine myosin X (green) and stained for actin filaments with rhodamine-phalloidin (red). Both endogenous and exogenous myosin X exhibit a striking localization to the tips of filopodia and retraction fiber-like structures (Bert et al. [2002]. J. Cell Sci. 113:3429-3451; Berg et al. [2002]. Nature Cell Biol. 4:246-250). Like myosin VII, the myosin X tail contains a MyTH4 domain and a FERM domain, though it is unique in containing three pleckstrin homology domains. Myosin X is widely expressed in vertebrate cells and tissues, although it is present at low levels. The motor domain is required for localization of GFP-myosin X to filopodial tips, and overexpression of full-length myosin X leads to increases in filopodial number and filopodial length. Intriguingly, myosin X can undergo two forms of movement in the filopodia. Puncta of GFP-myosin X can move forward (toward the tip) at a rate of approximately 100 nm/s. Rearward movements occur at rate of approximately 15 nm/s, which is very similar to retrograde flow rates. The PH domains of myosin X may play an important role in phagocytosis, as wortmannin treatment inhibits recruitment of myosin X to the phagocytic cup, and overexpression of the myosin X tail inhibits IgG-mediated phagocytosis (Cox et al. [2002], Nature Cell Biol. 4:469-477). Omar A. Quintero and Richard E. Cheney