Microtubules cytoplasmic

Gonc y We know of a requirement for astral microtubules, cytoplasmic dynein, the dynactin components p50and pi 50, as well as a protein called LET-99 (Hyman White 1987, Gonczy et al 1999b, Rose Kemphues 1998). 

PPP2R2A Ba PR55a, B55a Cytoskeleton (vimentin, microtubules), cytoplasm, nucleus, plasma membrane, Golgi, ER Widespread (testis) [23-27]... 

The influences of herbicides on cell division fall into two classes, ie, dismption of the mitotic sequence and inhibition of mitotic entry from interphase (G, S, G2). If ceU-cycle analyses indicate increases in abnormal mitotic figures, combined with decreases in one or more of the normal mitotic stages, the effect is upon mitosis. Mitotic effects usually involve the microtubules of the spindle apparatus in the form of spindle depolymerization, blocked tubulin synthesis, or inhibited microtubule polymerization (163). Alkaloids such as colchicine [64-86-8J,viahla.stiae [865-21-4] and vincristine [57-22-7] dismpt microtubule function (164). Colchicine prevents microtubule formation and promotes disassembly of those already present. Vinblastine and vincristine also bind to free tubulin molecules, precipitating crystalline tubulin in the cytoplasm. The capacities of these dmgs to interfere with mitotic spindles, blocking cell division, makes them useful in cancer treatment. 

Microfilaments and Microtubules. There are two important classes of fibers found in the cytoplasm of many plant and animal ceUs that are characterized by nematic-like organization. These are the microfilaments and microtubules which play a central role in the determination of ceU shape, either as the dynamic element in the contractile mechanism or as the basic cytoskeleton. Microfilaments are proteinaceous bundles having diameters of 6—10 nm that are chemically similar to actin and myosin muscle ceUs. Microtubules also are formed from globular elements, but consist of hoUow tubes that are about 30 nm in diameter, uniform, and highly rigid. Both of these assemblages are found beneath the ceU membrane in a linear organization that is similar to the nematic Hquid crystal stmcture. 

In this chapter we describe the distribution, assembly, and interaction of microfilaments and microtubules and their functional roles in cell movement and in the maintenance of the spatial organization of the cytoplasm. Also, the relative roles... 

Even though dynein, kinesin, and myosin serve similar ATPase-dependent chemomechanical functions and have structural similarities, they do not appear to be related to each other in molecular terms. Their similarity lies in the overall shape of the molecule, which is composed of a pair of globular heads that bind microtubules and a fan-shaped tail piece (not present in myosin) that is suspected to carry the attachment site for membranous vesicles and other cytoplasmic components transported by MT. The cytoplasmic and axonemal dyneins are similar in structure (Hirokawa et al., 1989 Holzbaur and Vallee, 1994). Current studies on mutant phenotypes are likely to lead to a better understanding of the cellular roles of molecular motor proteins and their mechanisms of action (Endow and Titus, 1992). 

Thus far, microtubules and actin filaments and their associated proteins have been discussed to advantage as independent cytoskeletal components. In actual fact, all of the components of the cytoskeleton (including intermediate filaments) are precisely integrated with one another (Langford, 1995), as well as with various cytoplasmic organelles, the nuclear membrane, the plasma membrane, and the extracellular matrix. In its totality the cytoskeleton subserves many coordinated and regulated functions in the cell ... 

Cell migration and cytoplasmic movement involve predominantly actin filaments in the locomotion of neutrophilic granulocytes, both actin filaments and microtubules in the elongation of neuronal growth cones and migration of neurites, and both actin and myosin in cytokinesis and the contraction of skeletal and cardiac muscle. 

Porter, K.R. (1966). Cytoplasmic microtubules and their functions. In Principles of Biomolecular Organization Ciba Foundation Symposia (Wolstenholme, G.E.W., O Connor, M., eds.), pp. 308-345. Little, Brown, Boston. 

Muscle biopsy with full histochemical and ultrastructural investigation is necessary for the confirmation of a diagnosis of IBM. The inclusions which are the hallmark of this disorder are to be found in three locations (a) basophilic granular inclusions are found at the periphery of vacuoles within the cytoplasm of muscle fibers (b) eosinophilic hyaline inclusions are also found in the cytoplasm but are not associated with vacuoles and (c) intranuclear inclusions consisting of aggregates of filamentous microtubules are found in a variable percentage of muscle nuclei. Inclusions of the first two types are visible at light microscope level, whereas the third type is detectable at the electron microscope level only. Ultrastructural... 

Nonmuscle cells perform mechanical work, including self-propulsion, morphogenesis, cleavage, endocytosis, exocytosis, intracellular transport, and changing cell shape. These cellular functions are carried out by an extensive intracellular network of filamentous structures constimting the cytoskeleton. The cell cytoplasm is not a sac of fluid, as once thought. Essentially all eukaryotic cells contain three types of filamentous struc-mres actin filaments (7-9.5 nm in diameter also known as microfilaments), microtubules (25 nm), and intermediate filaments (10-12 nm). Each type of filament can be distinguished biochemically and by the electron microscope. 

Microtubules, an integral component of the cellular cy-toskeleton, consist of cytoplasmic tubes 25 nm in diameter and often of extreme length. Microtubules are necessary for the formation and function of the mitotic spindle and thus are present in all eukaryotic cells. They are also involved in the intracellular movement of endocytic and exocytic vesicles and form the major structural components of cilia and flagella. Microtubules are a major component of axons and dendrites, in which they maintain structure and participate in the axoplasmic flow of material along these neuronal processes. 

Goncyy No. If this were the case, you would expect the side of the embryo to assume posterior character in the rare cases where sperm entry is lateral. Goldstein Hird (1996) showed this not to be the case. Instead, what they observed is that the male pronucleus and associated centrosomes move along the cell cortex towards the nearest pole, which then becomes the posterior of the embryo. This movement does not require cytoplasmic dynein function (P. Gonczy, unpublished observations) and may also be microtubule-independent. 

Gonczy After pronuclear migration and meeting of the pronuclei in the posterior half of the embryo, the pronuclei and associated centrosomes undergo a 90° rotation while going towards the centre of the embryo. This centration/ rotation process requires intact microtubules, as well as the function of cytoplasmic dynein and dynactin components (Hyman White 1987, Gonczy et al 1999a). 

Nurse With respect to the astral microtubules emanating towards the cortex, which are shorter in the gyg-8 mutant, are the pulling forces a consequence of the microtubules in wild-type being attached to the cortex, or are they due to attachment sites in the cytoplasm and associated motors, which means that if you extend longer into the cortex you would have a bigger pulling force than if you are shorter ... 

Belmont LD, Hyman AA, Sawin KE, Mitchison TJ (1990) Real-time visualization of cell cycle-dependent changes in microtubule dynamics in cytoplasmic extracts. Cell 62 579-589... 

FIGURE 4-7 A typical CNS myelinated fiber from the spinal cord of an adult dog. Contrast this figure with the PNS fiber in Figure 4-4. The course of the flattened oligodendrocytic process, beginning at the outer tongue (arrow), can be traced. Note that the fiber lacks investing cell cytoplasm and a basal lamina-as is the case in the PNS. The major dense line and the paler, double intraperiod line of the myelin sheath can be discerned. The axon contains microtubules and neurofilaments. 

---