The role of myosin in the structure and function of brush borders isolated from intestinal and colonic epithelial cells will be investigated. In the brush border cytoskeleton, myosin is associated with two structural domains: one comprising the terminal web where it crosslinks the microvillus core bundles of actin filaments, and the other a contractile ring of actin filaments that surrounds the terminal web. Two subsets of myosin are differentially extractable from the brush border: one that is involved in terminal web contraction and one that is not. The aim of this research is to determine the molecular basis for the two subsets. The possiblity that more than one isozyme of myosin is expressed in the brush border, and the relationship between myosin isozymes and the subsets of myosin will be investigated. The localization of each of the subsets of myosin with respect to the two major structural domains of the terminal web will also be determined. Because the circumferential ring is organized long before the interroolet region during embryogenesis, the findings on myosin isozyme expression and subset localization will be related to the normal sequence of intestinal development. Finally, the stable structural association of one myosin subset indicates the likelihood that it interacts with more than actin in the cytoskeleton. Proteins that bind myosin in the brush border will be identified and localized. The results of this research may indicate that myosin plays more than one role in brush border function and that a specific myosin performs a specific function within a single cytoskeletal system. This adds new significance to the general observation that cytoskeletal proteins are frequently encoded by multigene families.
