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  • 1
    Electronic Resource
    Electronic Resource
    Micromanipulation studies of the asyrnmetric positioning of the maturation spindle in Chaetopterus sp. Oocytes: I. Anchorage of the spindle to the cortex and migration of a displaced spindle (1988)
    New York, NY : Wiley-Blackwell
    Cell Motility and the Cytoskeleton 11 (1988), S. 83-96 
    Details
    ISSN: 0886-1544
    Keywords: unequal cell division ; spindle positioning ; spindle anchorage ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: We investigated the nature of the asymmetric positioning and attachment of Chaetopterus oocyte meiotic spindles to the animal pole cortex by micromanipulation. The manipulated spindle's behavior was analyzed in clarified oocyte fragments using video-enhanced polarized light microscopy. As the spindle was drawn towards the cell interior with a microneedle, the cell surface dimpled inwards adjacent to the outer spindle pole. As the spindle was pulled further inwards, the dimple suddenly receded indicating a rupture of a mechanical link between the cell cortex and outer spindle pole. The spindle paused briefly when released from the microneedle; then it spontaneously migrated back to the original attachment site and reassociated with the cell cortex. Positive birefringent astral fibers were seen running between the outer spindle pole and the cortex during the migration. The velocity of the spindle during its migration tended to increase as it came closer to the cortex. Velocities as high as 1.25 μm/sec. were measured. If removed too far from the attachment site cortex ( 〉 35 μm), the spindle remained stationary until pushed closer to the original attachment site. Spindles, inverted by micromanipulation, migrated and reattached to the cortical site by their former inner pole; thus either spindle pole can seek out and migrate to the original attachment site. However, spindle poles pushed against other cortical regions did not attach demonstrating that there is only one unique, localized attachment site for spindle attachment.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cm.970110202
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  • 2
    Electronic Resource
    Electronic Resource
    Reactivation of isolated mitotic apparatus: Metaphase versus anaphase spindles (1991)
    New York, NY : Wiley-Blackwell
    Cell Motility and the Cytoskeleton 18 (1991), S. 304-318 
    Details
    ISSN: 0886-1544
    Keywords: mitosis ; spindle ; chromosome ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Mitotic spindles isolated from sea urchin eggs can be reactivated to undergo mitotic processes in vitro. Spindles incubated in reactivation media containing sea urchin tubulin and nucleotides undergo pole-pole elongation similar to that observed in living cells during anaphase-B. The in vitro behavior of spindles isolated during metaphase and anaphase are compared. Both metaphase and anaphase spindles undergo pole-pole elongation with similar rates, but only in the presence of added tubulin. In contrast, metaphase but not anaphase spindles increase chromosome-pole distance in the presence of exogenous tubulin, suggesting that in vitro, tubulin can be incorporated at the kinetochores of metaphase but not anaphase chromosomes. The rate of spindle elongation, ultimate length achieved, and the increase in chromosome-pole distance for isolated metaphase spindles is related to the concentration of available tubulin. Pole-pole elongation and chromosome-pole elongation does not require added adenosine triphosphate (ATP). Guanosine triphosphate (GTP) will support all activities observed. Thus, the force generation mechanism for anaphase-B in isolated sea urchin spindles is independent of added ATP, but dependent on the availability of tubulin. These results support the hypothesis that the mechanism of force generation for anaphase-B is linked to the incorporation of tubulin into the mitotic apparatus. (If, in addition, a microtubule-dependent motor-protein(s) is acting to generate force, it does not appear to be dependant on ATP as the exclusive energy source).
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cm.970180407
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