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Biomedical subjects

D Bray

Publications and source records attributed to D Bray.

At least 91 records · Page 5Linked to original sources
PubMed1975

The actin content of fibroblasts.

Cultures of chick skin fibroblasts were dissolved in solutions of sodium dodecyl sulphate, and their entire protein content was examined by gel electrophoresis. The most abundant species migrated in the same position as muscle actin. It gave a similar pattern of iodinated peptides after reaction with radioactive sodium iodide and digestion with proteinases, and contained comparable amounts of Nt-methylhistidine. Its amount was estimated by quantitative densitometry of stained gels with bovine serum albumin as an internal standard, and by radioactive assay of cultures that had been grown in the presence of [35S]methionine. The values obtained ranged from 7 to 14% of the total cellular protein, with an average of 8.5%. A protein band in the position of muscle myosin was also present and accounted for about 2.5% of the total protein. Both this and the actin band increased in relative amount with the age of the cultures.

Actins↗
PubMed1973

Branching patterns of individual sympathetic neurons in culture.

The growth of single sympathetic neurons in tissue culture was examined with particular regard to the way in which the patterns of axonal or dendritic processes (here called nerve fibers), were formed. The tips of the fibers were seen to advance in straight lines and to grow at rates that did not vary appreciably with time, with their position in the cell outgrowth, or with the fiber diameter. Most of the branch points were formed by the bifurcation of a fiber tip (growth cone), apparently at random, and thereafter remained at about the same distance from the cell body. It seemed that the final shape of a neuron was the result of the reiterated and largely autonomous activities of the growth cones. The other parts of the cell played a supportive role but, apart from this, had no obvious influence on the final pattern of branches formed.

Animals↗
PubMed1970

Surface movements during the growth of single explanted neurons.

The processes of isolated rat sympathetic neurons growing in culture were marked with glass or carmine particles and observed with timelapse microphotography. Particles on the processes moved with the cell in relation to the dish and underwent continual small jerky movements. They did not, however, show any over-all distal motion and for long periods, during which the growth cone progressed more than 100 mu, the particles remained at about the same distance from the cell body. The most obvious explanation for this result is that new fiber surface, and perhaps the plasma membrane, is deposited in the region of the growing tip.

Animals↗
PubMed1967

Direction of chain growth in polysaccharide synthesis.

The biosynthesis of a bacterial polysaccharide-the surface O-antigen of Salmonella newington-differs in several respects from the more classical example of glycogen synthesis. Sugars are not transferred directly to the antigen from sugar nucleotide precursors but are transferred first into lipid-linked oligosaccharides. Growth of the polysaccharide chain then occurs by assembly of these lipid-linked precursors at the reducing end of the polymer rather than at its nonreducing end as in glycogen. This method of assembly, in which nascent chains are transferred to the next subunit, is analogous to the growth of proteins or fatty acids. It seems possible that these differences reflect the more complex requirements of a surface polysaccharide synthesized by membrane-bound enzymes. If this is the case, then several other polysaccharide systems may be synthesized by comparable mechanisms.

Antigens↗
PubMedDate not supplied

Rapid transport of foreign particles microinjected into crab axons.

The rapid transport of optically detectable organelles in axons has been well documented, although its molecular mechanism remains unknown. Here we report that synthetic particles microinjected into the giant axons of the shore crab, Carcinus maenas, are also transported, moving as though they were endogenous organelles. Polystyrene beads, polyacrolein beads, paraffin droplets and glass fragments, of sizes up to 0.5 micron in diameter, have been tested. Many of these foreign particles move rapidly and for long distances along the axon in the anterograde direction, travelling in a saltatory fashion, within a well defined velocity range. In many respects the movements are indistinguishable from those of anterogradely moving endogenous organelles seen by phase-contrast in these axons. Our results indicate that there is a transport system in axons capable of carrying almost any particle of suitable physical properties in an anterograde direction.

Acrolein↗
PubMedDate not supplied

Particle transport.

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Animals↗
PubMedDate not supplied

Assembly of microtubules at the tip of growing axons.

The growth of axons in the developing nervous system depends on the elongation of the microtubules that form their principal longitudinal structural element. It is not known whether individual microtubules in the axon elongate at their proximal ends, close to the cell body, and then move forward into the lengthening axon, or whether tubulin subunits are transported to the tip of the axon and assembled there onto the free ends of microtubules. The former possibility is supported by studies of slow axonal transport in mature nerves from which it has been deduced that microtubule assembly occurs principally at the neuronal cell body. By contrast, the polarity of microtubules in axons, which have their 'plus' or 'fast-growing' ends distal to the cell body, suggests that assembly occurs at the growing tip, or growth cone, of the axon. We have addressed this question by topically applying Colcemid (N-desacetyl-N-methylcolchicine), and other drugs which alter microtubule stability, to different regions of isolated nerve cells growing in tissue culture. We find that the sensitivity to these drugs is greatest at the growth cone by at least two orders of magnitude, suggesting that this is a major site of microtubule assembly during axonal growth.

Alkaloids↗