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J B Tucker

Publications and source records attributed to J B Tucker.

At least 19 recordsLinked to original sources
PubMed1992

A cell surface-associated centrosomal layer of microtubule-organizing material in the inner pillar cell of the mouse cochlea.

This investigation provides evidence that pericentriolar material is divorced from the immediate vicinities of centrioles and becomes functionally associated with the plasmalemma during the differentiation of a mammalian cell type. Such events occur prior to the assembly of large transcellular microtubule bundles in columnar epithelial cells called inner pillar cells in the mouse organ of Corti. The microtubules do not radiate from a typical centrosome and its centrioles. They elongate from a microtubule-organizing centre (MTOC), which is deployed as a subapical cell surface-associated layer in each cell. Most of the dense material of this layer, and the tops of most of the microtubules, are initially concentrated around the sides of a cell about 1 microns below its apical surface. In addition, a pair of centrioles is located above the layer, which acts as if it is a pericellular concentration of the pericentriolar material of a modified centrosome. Although microtubule nucleation takes place in a centrosome-like region, 13 protofilament fidelity is not exercised. Most of the microtubules have 15 protofilaments. Microtubule assembly progresses in these cells after the organ of Corti has been isolated for in vitro culture. However, large numbers of microtubules elongate from pericentriolar material juxtaposed against the centrioles. Hence, there is some reversion by the centrosomes of cultured cells to the operational configuration regarded as typical for animal tissue cells in general.

Animals↗
PubMed1991

Boxing: the preparticipation evaluation.

Boxing is a controversial sport that has drawn public and physician criticism since its inception in 900 BC. The American Medical Association has recently taken a formal position to ban boxing because of the alleged dangers, including the possibility of the long-term effect of dementia pugilistica. Proponents of amateur boxing are working diligently to document this claim both as premature and false. They cite amateur boxing's purpose as one boxer's attempt to outpoint or outscore his opponent by utilization of superior strength and skill. Despite this medical and political controversy, thousands of primary care patients are boxing. This report offers the physician guidelines for the preparticipation evaluation. Specific disqualifying conditions are addressed.

Boxing↗
PubMed1990

Taxol influences control of protofilament number at microtubule-nucleating sites in Drosophila.

Control of protofilament number has been investigated using Drosophila wings at a stage when 15-protofilament microtubules assemble under normal conditions. Microtubule nucleation still progressed at the usual microtubule-nucleating sites in the presence of taxol. However, provided taxol was introduced before microtubule nucleation began, few microtubules with 15 protofilaments assembled. Most microtubules were composed of 12 protofilaments (a previously undetected value for Drosophila) or 13 protofilaments (which is the value for microtubules in most eukaryotic cells). Unexpectedly, a comparatively mild challenge to control of nucleation (in vitro wing culture) also promoted assembly of 13-protofilament microtubules. Hence, the microtubule-nucleating sites may possess a relatively labile control specifying 15 protofilaments superimposed upon that for maintaining 13-protofilament fidelity.

Alkaloids↗
PubMed1989

Microtubule polarities indicate that nucleation and capture of microtubules occurs at cell surfaces in Drosophila.

Hook decoration with pig brain tubulin was used to assess the polarity of microtubules which mainly have 15 protofilaments in the transcellular bundles of late pupal Drosophila wing epidermal cells. The microtubules make end-on contact with cell surfaces. Most microtubules in each bundle exhibited a uniform polarity. They were oriented with their minus ends associated with their hemidesmosomal anchorage points at the apical cuticle-secreting surfaces of the cells. Plus ends were directed towards, and were sometimes connected to, basal attachment desmosomes at the opposite ends of the cells. The orientation of microtubules at cell apices, with minus ends directed towards the cell surface, is opposite to the polarity anticipated for microtubules which have elongated centrifugally from centrosomes. It is consistent, however, with evidence that microtubule assembly is nucleated by plasma membrane-associated sites at the apical surfaces of the cells (Mogensen, M. M., and J. B. Tucker. 1987. J. Cell Sci. 88:95-107) after these cells have lost their centriole-containing, centrosomal, microtubule-organizing centers (Tucker, J. B., M. J. Milner, D. A. Currie, J. W. Muir, D. A. Forrest, and M.-J. Spencer. 1986. Eur. J. Cell Biol. 41:279-289). Our findings indicate that the plus ends of many of these apically nucleated microtubules are captured by the basal desmosomes. Hence, the situation may be analogous to the polar-nucleation/chromosomal-capture scheme for kinetochore microtubule assembly in mitotic and meiotic spindles. The cell surface-associated nucleation-elongation-capture mechanism proposed here may also apply during assembly of transcellular microtubule arrays in certain other animal tissue cell types.

Animals↗
PubMed1988

Intermicrotubular actin filaments in the transalar cytoskeletal arrays of Drosophila.

Rabbit muscle myosin subfragment S1 decorates 6 nm diameter filaments in Drosophila wing epidermal cells in the arrowhead fashion characteristic of the binding of subfragment S1 to actin filaments. The filaments in question are concentrated between microtubules that are mostly composed of 15 protofilaments and form cell surface-associated transcellular bundles. There are indications that the majority of the actin filaments have the same polarity and that, like the microtubules, they may elongate from sites at the apical surfaces of the cells. The bundles of F actin and microtubules occur in dorsal and ventral epidermal cell layers of a wing blade. They are joined in dorso-ventral pairs by attachment desmosomes. These transalar cytoskeletal arrays may provide an example of a situation where actin filaments operate as stiffeners rather than active generators of force in conjunction with myosin. The arrays probably function as noncontractile pillars to maintain basal cell extensions and keep haemocoelic spaces open in the highly folded and expanding wing blades of late pupae.

Actins↗
PubMed1987

Evidence for microtubule nucleation at plasma membrane-associated sites in Drosophila.

This report is concerned with the nucleation and organization of microtubule bundles that assemble after 'conventional' centrosomal microtubule-organizing centres have been lost. The microtubule bundles in question span the lengths of wing epidermal cells. Bundles extend between hemidesmosomes at the apical cuticle-secreting surfaces of cells and basal attachment desmosomes that unite the dorsal and ventral epidermal layers of developing wing blades. Furthermore, each bundle includes up to 1500 microtubules and most of the microtubules are composed of 15 protofilaments. Individual cells were serially cross-sectioned at an early stage of bundle assembly. The number of microtubule profiles/cell cross-section decreased progressively by up to 59% of the most apical values in section sequences cut from fairly apical to more basal levels in the cells. The apical ends of microtubules were associated with numerous small dense plaque-like sites (diameter 0.1-0.2 micron), which were specialized regions of plasma membranes at the apical surfaces of cells. Many of the microtubules near apical plaques were not well aligned with each other; they 'radiated away' from cell apices. This was in contrast to the situation at more basal levels where most microtubules were oriented parallel to the longitudinal axes of cells. These findings indicate that the relatively dispersed arrays of apical plasma membrane-associated plaques act as microtubule-nucleating sites to initiate basally directed elongation of bundle microtubules. Apical cell surfaces and their plaques seem to operate as microtubule-nucleating and -organizing regions that functionally replace the centrosomal microtubule-organizing centres lost earlier in cell differentiation.

Animals↗
PubMed1986

Supracellular microtubule alignments in cell layers associated with the secretion of certain fish scales.

Intercellularly aligned microtubule arrays are present in cell layers associated with the growth and secretion of scales in the zebra fish Brachydanio rerio and the neon tetra fish Hyphessobrycon innesi. The layers in question are: the osteoblast layer that covers the ossified outer surface of a scale, and the layer of fibroblasts that is situated immediately underneath the inner collagenous surface of a scale's fibrillary plate. In certain osteoblasts, the proximal portions of microtubules (with respect to centrosomes) run closely alongside the anterior margin of each cell where it flanks one of a scale's ridge-shaped circuli. These osteoblasts and microtubule portions are arranged in aligned rows that are parallel to circuli. However, the distal portions of the microtubules curve into an orientation that is approximately at right angles to circuli and they are aligned with each other and similar microtubule portions in adjacent osteoblasts. Such microtubule alignments only occur in osteoblasts that are associated with circuli. In Hyphessobrycon osteoblasts situated elsewhere on a scale's surface, microtubules radiate from cell centres but their distal portions curve into alignment with each other and are oriented alongside cell margins. The proximal portions of fibroblast microtubules radiate from centrally positioned centrosomes but the distal portions curve into alignment with each other and distal microtubule portions in neighbouring fibroblasts. The overall pattern of microtubule alignment is similar to that of collagen fibres, which these fibroblasts are secreting onto the fibrillary plate. The immunofluorescence protocol that was used to demonstrate the microtubule alignments described above did not reveal such alignments in the osteoblast and fibroblast layers associated with scales of the brown trout Salmo trutta fario. These findings are assessed in terms of intra-and inter-cellular control of microtubule alignment, and decentralized reorientation of microtubules at distances of several micrometres from centrosomal microtubule-organizing centres. The functional significance of the relationships between microtubule alignment and supracellular patterns of alignment that take place as collagen deposition and ossification proceed during scale formation is also considered.

Animals↗
PubMed1986

Fieldside management of athletic injuries.

A physician trained in the management of sports-related injuries should be in attendance at athletic events with a potential for significant injury. These are usually contact sports, particularly football. While many of the expected injuries are orthopedic in nature, the risk of serious injury to the larynx, abdomen, eyes and teeth also exists.

Abdominal Injuries↗
PubMed1985

Spindle microtubule differentiation and deployment during micronuclear mitosis in Paramecium.

Spindles underwent a 12-fold elongation before anaphase B was completed during the closed mitoses of micronuclei in Paramecium tetraurelia. Two main classes of spindle microtubules have been identified. A peripheral sheath of microtubules with diameters of 27-32 nm was found to be associated with the nuclear envelope and confined to the midportion of each spindle. Most of the other microtubules had diameters of approximately 24 nm and were present along the entire lengths of spindles. Nearly all of the 24-nm microtubules were eliminated from spindle midportions (largely because of microtubule disassembly) at a relatively early stage of spindle elongation. Disassembly of some of these microtubules also occurred at the ends of spindles. About 60% of the total microtubule content of spindles was lost at this stage. Most, perhaps all, peripheral sheath microtubules remained intact. Many of them detached from the nuclear envelope and regrouped to form a compact microtubule bundle in the spindle midportion. There was little, if any, further polymerization of 24-nm microtubules after the disassembly phase. Polymerization of microtubules with diameters of 27-32 nm continued as spindle elongation progressed. Most microtubules in the midportions of well-elongated spindles were constructed from 14-16 protofilaments. A few 24-nm microtubules with 13 protofilaments were also present. The implications of these findings for spatial control of microtubule assembly, disassembly, positioning, and membrane association, that apparently discriminate between microtubules with different protofilament numbers have been explored. The possibility that microtubule sliding occurs during spindle elongation has also been considered.

Animals↗
PubMed1985

Modulation of epidermal cell shaping and extracellular matrix during caudal fin morphogenesis in the zebra fish Brachydanio rerio.

Distinct changes in epidermal cell shaping largely define the overall pattern of growth and form during generation of the ectodermal ridge and early stages of fin fold morphogenesis. The epidermal portion of the ridge and early fin fold are formed from a strip of epidermal cells that is only six to nine cells wide. There is apparently no increase in the number of these cells during initial formation of the ridge and its subsequent conversion into a fin fold which contains extracellular matrix fibres. Epidermal cells adopt a wedge-shaped morphology during ridge production. Distinct changes in the shaping and contact relationships between basal portions of these cells generate intercellular spaces at several discrete loci within the ridge. These spaces become continuous with each other to form a subepidermal space. Hence, the subepidermal space is not produced by straight-forward folding of an epidermal sheet. Cells flanking the sides of the ridge start to flatten as it is converted into a fin fold. A continuous row of distinctive cells is positioned along the apex of the developing fold. The term 'cleft cells' is suggested for these apical cells. Each cleft cell retains a wedge-shaped form during fold formation and develops a basal cleft-shaped invagination. Invaginations are aligned in neighbouring cleft cells so that these cells cap the distal boundary of the subepidermal space where collagenous extracellular fibres called actinotrichia run anteroposteriorly along the length of the fin fold. This orientation is in direct contrast to the proximodistal orientation of actinotrichia within the remainder of the subepidermal space. During early stages of fold production a temporary set of previously unreported extracellular cross fibres spans the subepidermal space at right angles to actinotrichia. These configurations of extracellular fibres could be advantageous for maintaining the structural integrity of the early fin fold.

Animals↗
PubMed1979

Changes in microtubule packing during the stretching of an extensible microtubule bundle in the ciliate Nassula.

The cytopharyngeal sheath in the ciliate Nassula is a long hollow tube-shaped microtubule bundle that forms part of a large feeding organelle called the cytopharyngeal basket. During the initial stages of ingestion of algal filaments by Nassula the sheath is stretched, becomes approximately elliptical in cross-section, and its external cross-sectional perimeter increased by a factor of about two. The mean circumferential centre-to-centre spacing of radially oriented rows of sheath tubules increases from 57 to 137 nm during stretching but sheath thickness and the radial spacing of sheath tubules do not change appreciably. It is suggested that extensible circumferentially oriented intertubule links and relatively inextensible radial links may define the anisometric mechanical properties of this particular microtubule bundle which are related to its cytoskeletal role. The possibility that extensible links resist stretching elastically and provide the restoring forces for return of the sheath to its former shape and dimensions after stretching is considered.

Animals↗
PubMed1977

Control of shape and pattern during the assembly of a large microtubule bundle. Evidence for a microtubule-nucleating-template.

Microtubules are packed and linked together in a well defined hexagonal arrangement in the cytopharyngeal microtubule bundles of the ciliate Nassula. Early stages in the morphogenesis of these bundles have been examined. Elements which nucleate assembly of bundle microtubules are apparently closely associated before tubule assembly commences. These nucleating elements seem to be bound together in highly ordered arrays to form microtubule-nucleating-templetes. Each array of elements is attached to the proximal end of a basal body and appears to establish the pattern of tubule packing and cross-sectional shape of a tubule bundle. A self-assembly procedure which accounts for the anisometric growth and shaping of a template and its microtubule bundle is proposed.

Animals↗
PubMed1976

Microtubules and control of insect egg shape.

This study evidence for tension transmission by microtubules and desmosomes in the follicular epithelium during anisometric growth of certain insect eggs. Most insect oocytes, and the follicles which surround them, grow anisometrically as they assume shapes which approximate to those of long prolate spheroids. Surface growth is most rapid in directions which parallel the polar axis of an oocyte and slowest in circumferential directions at right angles to this axis. The longitudinal axes of microtubule bundles in follicle cells of the gall midge Heteropeza and the cockroach Periplaneta are oriented circumferentially with respect to the surfaces of developing eggs and at right angles to the polar axes of eggs. At cell boundaries, the tubules appear to be attached to spot desmosomes. It is suggested that microtubules and desmosomes form a mechanical continuum throughout a follicular epithelium which transmits tensile forces around the circumference of a growing egg. Follicular resistance to circumferential expansion may be largely responsible for defining the elongate form of insect eggs.

Animals↗