ESOTAXIS: IDENTIFYING THE FACTORS THAT INFLUENCE NANOTOPOGRAPHIC GUIDANCE OF THE DYNAMICS AND ORGANIZATION OF THE ACTIN CYTOSKELETON AND OTHER MOLECULES INVOLVED IN DIRECTED CELL MIGRATION

Abstract

Directed migration is a crucial capability of cells in developmental and immunological processes. Defects in cell migration can lead to negative health outcomes. Cell motion depends on the organization and dynamics of internal components, especially the actin cytoskeleton, and the extracellular environment. Microscale and nanoscale topographical cues, with at least one dimension that is much smaller than most cells, can bias cell motion over long distances, due to the guidance of the organization and dynamics of the cytoskeleton and other molecules and assemblies within the cell. In this work, I describe a technique to reproduce patterned nanotopographic substrates for use in the study of esotaxis, the guided organization and dynamics of the actin cytoskeleton and other cellular components in response to nanotopographic cues. The guidance of actin drives directed cell motion along a pattern with dimensions much smaller than the cell. The dimensions of the nanotopography determine the extent to which cellular components are guided. Differences in the physical properties of the plasma membrane and the actin cytoskeleton among cell lines will influence the extent of guidance by nanotopography. Asymmetric patterns can accentuate the distinctions in esotactic responses among cell lines and drive contact guidance in different directions. The cytoskeletal response to nanotopography is a local phenomenon. A cell in contact with multiple nanotopographic cues simultaneously will show distinct organization of actin in the different regions of the cell. The importance of local actin dynamics requires an analysis method, optical flow, that can identify and track the distinct cytoskeletal motions in different parts of the cell. The formation of adhesions attached to the extracellular matrix is a characteristic of the migratory behavior of many types of cells and these adhesions are credited with allowing the cell to sense and interact with the underlying substrate. Actin can sense nanotopographic cues without the widespread availability of adhesive ligands. Although adhesion to the substrate strongly increases the extent of cell spreading and migration on nanoridges, epithelial cells can align with and migrate along nanotopography even with a dearth of adhesive cues. Therefore, actin is a supreme sensor of nanotopography that can drive directed cell migration.