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FO CUS ON CYTOSKELETAL DYNAMICS
THE CO-WORKERS OF ACTIN FILAMENTS: FROM CELL STRUCTURES TO SIGNALS
Cline Revenu, Rafika Athman, Sylvie Robine and Daniel Louvard
Cells have various surface architectures, which allow them to carry out different specialized functions. Actin microfilaments that are associated with the plasma membrane are important for generating these cell-surface specializations, and also provide the driving force for remodelling cell morphology and triggering new cell behaviour when the environment is modified. This phenomenon is achieved through a tight coupling between cell structure and signal transduction, a process that is modulated by the regulation of actin-binding proteins.
PHAGOCYTOSIS
An actin-dependent process by which cells engulf external particulate material by extension and fusion of pseudopods.
MICROVILLI
Small, finger-like projections (12 m long and 100 nm wide) that occur on the exposed surfaces of epithelial cells to maximize the surface area.
STEREOCILIA
Tapered, finger-like projections from hair cells of the inner ear that respond to mechanical displacement with alterations in membrane potential, and thereby mediate sensory transduction.
The integrity of the actin cytoskeleton is essential for cells to form and maintain their shape and structure. The remodelling of the cytoskeleton in dynamic cellular processes produces changes in cell shape and motility in response to external stimuli, and is therefore involved in signal transduction. These features of the actin cytoskeleton are regulated by a cohort of actin-binding proteins (ABPs), which were initially considered to be structural components that organize a stable actin cytoskeleton, but are now known to be regulators of cellular dynamics and key components of signalling processes.
Our increasing understanding of actin dynamics has revealed the biological complexity of cell behaviour and prompted us to investigate cell functions in a whole tissue or organ. For instance, actin dynamics are required for the absorptive function of the intestinal epithelium, for mechanosensing in the inner ear, for orientated nerve and capillary growth, and during defence processes that involve PHAGOCYTOSIS,migration and the
activation of immunologically competent cells. The actin cytoskeleton is also essential for cell-motility events that are required for normal organogenesis and that occur in pathophysiological processes such as wound repair or tumour-cell migration (metastasis).
In this review, we tackle the issue of the complexity of the actin cytoskeleton in plasma-membrane specializations, as well as actin...