Microtubules and Microfilaments: The Cell Cytoskeleton

Abstract

The cytoskeleton, the structural framework of the cell, was thought, about twenty years ago, to be represented by a few fibrillar proteins, the best known being those of muscle and keratinised cells (cf. De Robertis et al., 1960). New techniques — mainly electron microscopy, gel electrophoresis and immunohistochemistry — have demonstrated that most cells have an extensive number of fibrils in their cytoplasm, and many new cytoskeletal proteins are discovered each year. Structural proteins of the nucleus will not be considered here: our purpose is to give a summary of the main skeletal elements of the cytoplasm, as found in most cells. We will consider first those fibrillar structures which are found in nearly all Eukaryotic cells: microtubules, intermediary microfibrils, and contractile proteins of the actin type. A short list of other skeletal proteins will be given next, although the pace of recent discoveries — as evidenced for instance by the Second International Congress on Cell Biology held in September 1980 — is an indication of the growing complexities of the subject.