[Functional significances of the cytoskeleton]

Functional significances of the cytoskeleton and the plasmalemmal undercoat are discussed with special reference to their ultrastructural aspects. The cytoskeleton is mainly composed of three distinctive cytoplasmic fibrous structures, namely, microtubules, actin filaments and intermediate filaments. Closely associated with such fibrous structures are a variety of proteins, which have been shown not only to control the formation or breakdown of the fibrous structures but also to involve the construction of a higher order of fibrous architectures such as bundles and networks. Thus, these cytoskeletal fibrous components may form the respective systems, though such systems often interact with each other for the cytoplasmic integrity. The fundamental function of the cytoskeleton is to provide structural frameworks for the cytoplasm. Through such frameworks the cytoskeleton is involved in various cellular organizations and activities such as cell shape, distribution of cell organelles, cell motility, membrane phenomena, and metabolism. Much interest has also been drawn to the interaction between the plasmalemma and the cytoskeleton. Part of such interaction can be assigned to the plasmalemmal undercoat, though it indeed constitutes a part of the cytoskeleton. The significance of the plasmalemmal undercoat may be to primarily provide structural supports for the plasmalemma, playing various roles in cell physiology.