Cell locomotion types

Cells make use of many different types of membranes. All cells have a cytoplasmic membrane, or plasma membrane, that functions (in part) to separate the cytoplasm from the surroundings. In the early days of biochemistry, the plasma membrane was not accorded many functions other than this one of partition. We now know that the plasma membrane is also responsible for (1) the exclusion of certain toxic ions and molecules from the cell, (2) the accumulation of cell nutrients, and (3) energy transduction. It functions in (4) cell locomotion, (5) reproduction, (6) signal transduction processes, and (7) interactions with molecules or other cells in the vicinity. 

Microtubules are universally present in eukaryotes from protozoa to the cells of higher animals and plants (Porter, 1966 Hardham and Gunning, 1978 Lloyd, 1987), but they are absent in mammalian erythrocytes and in prokaryotes. Microtubules participate in a number of cellular functions including the maintenance of cell shape and polarity, mitosis, cytokinesis, the positioning of organelles, intracellular transport to specific domains, axoplasmic transport, and cell locomotion. The diversity of microtubule fimctions suggests that not all microtubules are identical and that different classes of microtubules are present in different cell types or are localized in distinct domains in the same cell type (Ginzburg et al., 1989). 

Tubulins arose very early during the course of evolution of unicellular eukaryotes and provide the machinery for the equipartitioning of chromosomes in mitosis, cell locomotion, and the maintenance of cell shape. The primordial genes that coded for tubulins likely were few in number. As metazoan evolution progressed, natural selection processes conserved multiple and mutant tubulin genes in response to the requirements for differentiated cell types (Sullivan, 1988). 

The Locomotion of Amoeba The Locomotion of Fibroblastic Cell Types The Locomotion of Leukocytes The Behavior of Locomoting Cells The Role of the Cytoskeleton in Cell Locomotion The Microtubule-Based Cytoskeleton The Intermediate Filament-Based Cytoskeleton The Microfilament-Based Cytoskeleton The Organization of Microfilaments in Cells Microfilament Dynamics and Cell Locomotion Sites of Lamellar Protrusion May Be Determined by the Nucleation of Actin Polymerization... 

Protein Cell Type/Organism Expression Level Effect on Cell Locomotion Reference... 

The uPA receptor also appears to play a role in cell locomotion and chemo-taxis, at least for human monocytes in vitro (G8). Using these cells, chemotaxis was inhibited by pretreatment with both anti-uPA receptor antibodies and anti-sense uPA receptor oligonucleotides. Expression of uPA catalytic activity was not required for chemotaxis with this cell type (G8). 

Although cells sometimes are spherical, they more commonly have more elaborate shapes due to their internal skeletons and external attachments. Three types of protein filaments, organized into networks and bundles, form the cytoskeleton within animal cells (Figure 1-15). The cytoskeleton prevents the plasma membrane of animal cells from relaxing into a sphere (Chapter 5) it also functions in cell locomotion and the intracellular transport of vesicles, chromosomes, and macromolecules (Chapters 19 and 20). The cytoskeleton can be linked through the cell surface to the extracellular matrix or to the cytoskeleton of other cells, thus helping to form tissues (Chapter 6). 

The cytochalasins are a group of metabolites produced by certain fungi (e.g., Helminthosporium dermatoideum) that inhibit actin-dependent types of cell movement such as leukocyte locomotion, phagocytosis, cytokinesis, the retraction of... 

A factor known as scatter factor has been characterized which causes the break up and stimulates motility of epithelial cell clumps (Stoker et al., 1987). This factor is identical to hepatocyte growth factor and increases the rate of locomotion of several other cell types. Motility factors elaborated from tumor cells are considered to play an important role in metastasis (see later). Guidance of cells by the physical topography of the substratum is another factor that profoundly affects the behavior of cells. 

In the cells of this tissue, which are known as fibres, the two major proteins, actin and myosin, are orgaiused to form myofibrils. These are structural rods that can contract (Figure 1.11). This enables muscle cells to shorten, which provides for movement and locomotion (Figure 1.12). There are three types ... 

All eucaryotic cells contain various proteins in their cytoplasm that interact to form mechanically stabilizing structures. The amounts of these proteins differ with cell type, and the structural elements - collectively referred to as the cytoskeleton -can be very labile. Labile transformations of cytoskeletal networks are involved in such essential biological phenomena as chromosome movement and cell division, intracellular material transport, shape changes relating to tissue development, and amoeboid-like locomotion (1-3). A great deal of work in recent years has led to the biochemical characterization of numerous cytoskeletal proteins(A) and the elucidation of their spatial localization within a cell(2). However, few quantifiable models yet exist that are appropriate for incorporating that information into notions of shape transformation and cell movement(5-8). 

Extracellular matrices (ECM) are the primary structural materials found in connective tissue in vertebrates that serve to maintain tissue shape (skin), aid in locomotion (bone), transmit and absorb mechanical loads (tendon and ligament), prevent premature mechanical failure (tendon, ligament, skin, and blood vessel wall), partition cells and tissues into functional units (fascia), act as scaffolds that define tissue and organ architecture (organ parenchyma), act as storage devices for elastic energy (tendon and blood vessel wall), and as the substrate for cell adhesion, growth, and differentiation of a variety of cell types. 

Bone is a vital, dynamic connective tissue which has evolved to reflect a balance between its two major functions, provision of mechanical integrity for locomotion and protection and involvement in the metabolic pathways associated with mineral homeostatis. In addition, bone is the primary site of hemopoiesis and recent findings support its important role as a component of the immune system [1]. Bones continuously mend and rebuild themselves by opposing actions of two types of cells, the osteoblasts that form bone and the osteoclasts that resorb (destroy) bone. When the activity of the bone destroying osteoclast cell outpaces that of bone forming osteoblasts, the bottom line is bone loss and the result is osteoporosis. 

Microfilaments, which are small (5-7 nm in diameter) fibers composed of the protein actin, perform their functions by interacting with certain cross-linking proteins. Important roles of microfilaments include involvement in cytoplasmic streaming (a process that is most easily observed in plant cells in which cytoplasmic currents rapidly displace organelles such as chloroplasts) and ameboid movement (a type of locomotion created by the formation of temporary cytoplasmic protrusions). 

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