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Biomedical subjects

W D Cohen

Publications and source records attributed to W D Cohen.

At least 37 records · Page 2Linked to original sources
PubMed1982

The cytoskeletal system of nucleated erythrocytes. II. presence of a high molecular weight calmodulin-binding protein.

Calmodulin was detected in dogfish erythrocyte lysates by means of phosphodiesterase activation. Anucleate dogfish erythrocyte cytoskeletons bound calmodulin. Binding of calmodulin was calcium-dependent, concentration-dependent, and saturable. Cytoskeletons consisted of a marginal band of microtubules containing primarily tubulin, and trans-marginal band material containing actin and spectrinlike proteins. Dogfish erythrocyte ghosts and cytoskeletons were found to contain a calcium-dependent calmodulin-binding protein, CBP, by two independent techniques: (a) 125I-calmodulin binding to cytoskeletal proteins separated by SDS PAGE, and (b) in situ azidocalmodulin binding in whole anucleate ghosts and cytoskeletons. CBP, with an apparent molecular weight of 245,000, co-migrated with the upper band of human and dogfish erythrocyte spectrin. CBP was present in anucleate ghosts devoid of marginal bands and absent from isolated marginal bands. CBP therefore appears to be localized in the trans-marginal band material and not in the marginal band. Similarities between CBP and high molecular weight calmodulin-binding proteins from mammalian species are discussed.

Animals↗
PubMed1980

Association of centrioles with the marginal band of a molluscan erythrocyte.

Continuous circumferential bundles of microtubules, or marginal bands (MBs), are best known as a prominent structural feature of all nonmammalian vertebrate erythrocytes and mammalian blood platelets. Since their discovery in the late 19th century, MBs have been thought to play a cellular morphogenetic role, but no cytological clues to the mechanism of MB biogenesis have been reported. In previous work we have established the presence of MBs in serveral invertebrate blood cell types, including amebocytes and coelomocytes of certain Arthropod species and erythrocytes of a Sipunculan. We report here the occurrence of MBs in erythrocytes of the ark Anadara transversa (Mollusca) and four closely related species. The MBs of these arks have a striking structural feature; each is physically associated with a pair of centrioles. The centrioles are identified as such on the basis of morphological criteria: size, cylindrical shape, right-angle orientation, pairing, and 9-triplet ultrastructure. This intimate association between centrioles and MBs suggests that centrioles may be MB-organizing centers and invites comparative investigation of their possible role in vertebrate erythrocyte and platelet morphogenesis.

Animals↗
PubMed1979

Marginal bands in camel erythrocytes.

The elliptical, anucleate erythrocytes of camels have been examined for the presence of marginal bands and their constituent microtubules. Lysis of erythrocytes under microtubule-stabilizing conditions readily revealed marginal bands in at least 3 % of the cells, as observed by phase-contrast and darkfield light microscopy. Microtubules plus a marginal band-encompassing network of material are visible in lysed cell whole mounts with transmission electron microscopy. Marginal band microtubules are also evident in electron micrographs of thin-sectioned camel erythrocytes identifiable as reticuloyctes on the basis of submaximal electron density (reduced haemoglobin iron content) and presence of polysomes. The results suggest that marginal bands may be involved in morphogenesis of camel erythrocytes but are not required for maintenance of their ellipticity after cells are fully differentiated.

Animals↗
PubMed1978

Observations of the marginal band system of nucleated erythrocytes.

The marginal band (MB) of nucleated erythrocytes (thos of nonmammalian vertebrates) is a continuous peripheral bundle of microtubules normally obscured by hemoglobin. Treatment of these elliptical cells with modified microtubule polymerization media containing Triton X-100 yields a semilysed system in which MB, nucleus, and trans-MB material (TBM) are visible under phase contrast. The TBM apparently interconnects structural components, passing around opposite sides of the nucleus and suspending it in native position. In uranyl acetatestained whole whole mounts (goldfish) examined by transmission electron microscopy, the TBM appears as a network. MBs of semilysed cells are relatively planar initially, but twist subsequently into a range of "figure-8" shapes with one of the two possible mirror-image configurations predominant. Nuclei and MBs can be released using proteolytic enzymes, to which the TBM seems most rapidly vulnerable. MBs thus freed are birefringent, generally untwisted, and much more circular than they are in situ. As a working hypothesis, it is prosposed that the flattened, elliptical shape of nucleated erythrocytes is a result of TBM tension applied asymmetrically across an otherwise more circular MB, and that the firure-8 configuration occurs when there is extreme TBM shrinkage or contraction.

Animals↗
PubMed1978

On erythrocyte morphology.

The significance of the distinctive morphological difference between mammalian and non-mammalian vertebrate erythrocytes (disc versus ellipse) is discussed in the light of mammalian erythrocyte rheology.

Animals↗
PubMed1977

Mitotic spindles of Drosophila melanogaster: a phase-contrast and scanning electron-microscope study.

Mitotic spindles have been isolated from the blastema stage of Drosophila melanogaster embryos using modified tubulin-polymerizing medium. 'Clean' spindles, relatively free of contaminating cytoplasmic material, are obtained. Under phase contrast, mitotic stages appear remarkably similar to those seen in situ, as reported in early literature. This preservation of morphological integrity, coupled with relative structural simplicity due to low chromosome number (2n = 8), makes these spindles ideal subjects for study. Use of the scanning electron microscope provides excellent visulization of their general structural organization, changes in whole spindle structure during the course of mitosis, and higher resolution viewing of surface detail than is permitted with light microscopy.

Drosophila melanogaster↗