Microtubular Organization in Elongating Myogenic Cells

Warren, Robert H.

doi:10.1083/jcb.63.2.550

Cited by 91 publications

(63 citation statements)

References 46 publications

(57 reference statements)

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“…Previous studies on the equilibrium nature of microtubule polymerization suggested a mechanism of condensation-polymerization characterized by distinct phases of nucleation and growth (17,22). Since purified tubulin subunits were capable of rapid addition onto preexisting microtubule fragments and because HMW-free tubulin did polymerize slowly, these results and the work of Kirschner et al (23) (26) and in developing myoblasts (5) indicate that these arrays consist primarily of short, overlapping tubule fragments. These studies suggest that the structural integrity of the overall microtubule array requires lateral interaction between paraxial tubules.…”

Section: Discussionsupporting

confidence: 68%

“…For some of these functions microtubule-associated elements such as crossbridges have been postulated (2,3), and structural components attached to microtubules have been observed in neurons (4), myoblasts (5), and the mitotic spindle (6,7). Although a microtubule sidearm which produces the force for axonemal motility has been isolated from cilia and flagella (8), in no case have the structural components observed on cytoplasmic microtubules been characterized biochemically or had their exact functions defined.…”

mentioning

confidence: 99%

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Association of high-molecular-weight proteins with microtubules and their role in microtubule assembly in vitro.

Murphy¹,

Borisy²

1975

Proc. Natl. Acad. Sci. U.S.A.

491

232

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High-molecular-weight components (HMW) specifically associated with microtubule protein purified from porcine brain tissue were separated from tubulin by DEAE-Sephadex ion exchange chromatography. Analysis by viscometry, sedimentation, and electron microscopy of the unfractionated microtubule protein, separated HMW and tubulin fractions, and reconstituted mixtures showed that HMW promoted formation of ring structures at 50 and tubule polymerization at 370. The HMW reassociated with tubulin and was identified in thin sections as 18.9 X 5.6 nm projections attached to the microtubules with a longitudinal periodicity of 32.5 nm. These studies: (1) indicate that the HMW fraction stimulates microtubule assembly by facilitating the formation of ring structures which are apparently intermediates in polymerization, and (2) demonstrate that the HMW associates with microtubules as a structural component projecting from the surface of the microtubule wall.Cytoplasmic microtubules play important roles in cell elongation and motile processes such as mitosis and intracellular transport (1). For some of these functions microtubule-associated elements such as crossbridges have been postulated (2, 3), and structural components attached to microtubules have been observed in neurons (4), myoblasts (5), and the mitotic spindle (6, 7). Although a microtubule sidearm which produces the force for axonemal motility has been isolated from cilia and flagella (8), in no case have the structural components observed on cytoplasmic microtubules been characterized biochemically or had their exact functions defined.Microtubule-associated proteins have been observed in preparations of purified microtubule protein obtained from brain tissue by an in vitro assembly procedure (9, 10). These components account for 15-20% of the total purified material and are typically resolved on 5% acrylamide gels as a pair of closely spaced bands (286,000 and 271,000 MW) together with a minor band of higher molecular weight (345,000 MW). We refer to these bands collectively as high-molecular-weight components (HMW). Bands of high molecular weight have also been observed by others using a similar assembly procedure (11-13), an assembly procedure using glycerol (14), and in purified tubule preparations stabilized in hexylene glycol (15). Previous results showed that the HMW components copurified in constant stoichiometry with tubulin through repeated cycles of assembly-disassembly (9,10,14). Agents that inhibited microtubule assembly also inhibited the sedimentation of the HMW under conditions that sedimented microtubules but not the unpolymerized material (10). Therefore, we concluded that these components were not contaminants but rather were specifically associated with microtubules. The HMW components were therefore further investigated to determine the nature of their association with microtubules and their effect on tubule assembly in vitro. MATERIALS AND METHODSPreparation of HMW and Tubulin Fractions. Purified microtubule protein was obtained from p...

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Section: Discussionsupporting

confidence: 68%

mentioning

confidence: 99%

Association of high-molecular-weight proteins with microtubules and their role in microtubule assembly in vitro.

Murphy¹,

Borisy²

1975

Proc. Natl. Acad. Sci. U.S.A.

491

232

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“…In general, fibroblasts in culture contain abundant microtubules that are rapidly destroyed by such drugs or mitotic inhibitors as colchicine, Colcemid, and the vinca alkaloids (25-27). In addition, the correlation between elongation of eukaryotic cells and alignment of longitudinally oriented microtubules has been observed in most of the cell systems studied (28)(29)(30). as we have shown in this study, parallel conditions that preserve extensive elongated microtubules in CHO cells (21-23) inhibit synchronous rhythmic contractions of myocytes in culture.…”

Section: Discussionmentioning

confidence: 63%

Relationship between dibutyryl cyclic AMP and microtubule organization in contracting heart muscle cells.

Nath¹,

Shay²,

Bollon³

1978

Proc. Natl. Acad. Sci. U.S.A.

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Rhythmic and synchronous contractions of interconnecting myocyte cultures prepared from fetal rat hearts are arrested upon the addition of 0.2-2.0 mM N6,02'-dibutyryladenosine 3':5'-cyclic monophosphate (Bt2cAMP). The contractions arrested by Bt2cAMP are restored either by diluting the Bt2cAMP from the media or by adding colchicine. While colchicine restores Bt2cAMP-arrested myocyte contractions at concentrations as low as 1.0 jIM, the inactive isomer lumicolchicine shows no effect. Morphologically, Bt2cAMP treatment of myocyte cultures results in the appearance of numerous elongated cellular processes not present in control cultures. Ultrastructural examination indicates that in Bt2cAMP-treated cells the intracellular distribution of microtubules is altered such that these organelles appear to accumulate in parallel arrays. In cells not treated with Bt2cAMP, the microtubules appear randomly oriented, while in cells treated with only colchicine, intact microtubules are not observed. The relationship between microtubules and heart cell contraction is discussed. When embryonic heart tissue is dissociated with proteolytic enzymes into single cells and then grown in primary culture, a substantial fraction of the cells display spontaneous and rhythmic contractions (1-4). The time required for the onset of autorhythmicity of primary heart cell cultures is related to the age of the embryo used as the source of the dissociated heart cells (1, 5). A second property of the cultured myocyte system is that the cells of auricular origin contract faster than ventricular cells (1, 6). Thus, the specificity of the compartments of whole heart also manifests itself through the individual cells. Other interesting properties of myocyte cultures are the ability of myocytes to grow independently of each other and beat at individual rates, or the formation of a synchronously beating network of interconnected heart cells achieved by cell contact and possibly multiplication (7,8).The primary myocyte culture has been used as a model for the automaticity and coordinated rhythmic contractile activity of the intact heart with respect to the action of various chronotropic agents such as drugs and hormones (4, 9, 10). In this report, we show that the rhythmic myocyte contraction in culture is reversibly inhibited by 0.2-2.0 mM N6,02'-dibutyryl cyclic AMP (Bt2 cAMP). Colchicine, an inhibitor of microtubule formation, restores the synchronous contraction of Bt2-cAMP-treated myocytes, although the inactive isomer lumicolchicine does not. In addition, this report presents ultrastructural observations indicating that in Bt2cAMP-treated myocyte cultures the intracellular distribution of microtubules is altered such that these organelles appear to accumulate in parallel arrays, while in control cultures the microtubules appear randomly oriented. MATERIALS AND METHODSPreparation of Myocyte Cultures. Minced ventricular muscles dissected from 19-day-old embryos of Sprague-Dawley rats were disaggregated by repeated incubation with 0.25% pancreat...

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“…10). Similar distribution patterns have been observed in skeletal muscle fibers (2,12,21,32,33) and in cardiac muscle cells (4,8,19,34). Goldstein and Entman (8) have also described MTscoiled in a helical fashion encircling myofibrils in cardiac muscle cells, but no such arrangement could be detected in our materials.…”

Section: Discussionmentioning

confidence: 47%

“…MTsare remarkably abundant in developing muscle cells (1,5,32,33). Thus much attention has been paid to the role of MTsin myogenesis.…”

mentioning

confidence: 99%

The Distribution and Arrangement of Microtubules in Mammalian Skeletal Muscle Fibers.

Kano

Fujimaki

Ishikawa

1991

Cell Struct. Funct.

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ABSTRACT. The distribution and arrangement of microtubules (MTs) in skeletal muscle fibers of the rat and mousediaphragm were examined by thin-section electron microscopy. In the central portion of muscle fibers, most MTsran longitudinally between myofibrils and beneath the sarcolemma, and some MTsran transversely predominantly at the level of the I band, especially of the A-I junction, thus forming a lattice-like arrangement. At the fiber periphery, MTswere aggregated in the perinuclear region, from which they radiated to take a longitudinal course beneath the sarcolemma and to run in a transverse direction at the I-band level. In the end portion of muscle fibers, MTswere abundant and ran longitudinally into sarcoplasmic processes. MTswere often found to be spatially associated with membranousorgandies. Quantitative analyses indicated that the longitudinally running MTswere remarkably more numerous in the peripheral zone of muscle fibers than in the deeper zones. The density of MTsin the central portion was almost the same in both red and white muscle fibers. The density was significantly higher at the fiber ends, though it varied considerably among different fibers. These results are discussed with special reference to the possible involvement of MTsin intracellular transport as well as structural support.Microtubules (MTs) are one of the major components of the cytoskeleton and are believed to primarily provide structural supports in various types of cells. Thus MTs are involved not only in the maintenance of cell shape but also in various cellular movements such as ciliary movement, cell division, and intracellular transport (for reviews see 3, 17, 18, 20).Skeletal muscle fibers are highly specialized cells.Most of the cytoplasm (sarcoplasm) is occupied by the contractile material called cross-striated myofibrils. Membranousorganelles such as the sarcoplasmic reticulum and T-system are also regularly arranged in register around and between the myofibrils. Skeletal muscle fibers contain numerous nuclei, which are usually located at the fiber periphery. It is interesting to ask how the structural integrity, contractile activity, and metabolism are maintained in such multinucleate, giant cells.Of particular interest is the process of intracellular transport, including the nucleus-sarcoplasm interaction, with special reference to the possible functions of MTs. MTsare remarkably abundant in developing muscle cells (1,5,32,33). Thus much attention has been paid to the role of MTsin myogenesis. In definitive myo-* To whomcorrespondance should be addressed. !) Present address:

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Microtubular Organization in Elongating Myogenic Cells

Cited by 91 publications

References 46 publications

Association of high-molecular-weight proteins with microtubules and their role in microtubule assembly in vitro.

Association of high-molecular-weight proteins with microtubules and their role in microtubule assembly in vitro.

Relationship between dibutyryl cyclic AMP and microtubule organization in contracting heart muscle cells.

The Distribution and Arrangement of Microtubules in Mammalian Skeletal Muscle Fibers.

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