Cameron Lisa

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Cameron
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Lisa
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  • Article
    Bipolarization and poleward flux correlate during xenopus extract spindle assembly
    (American Society for Cell Biology, 2004-09-22) Mitchison, Timothy J. ; Maddox, P. ; Groen, Aaron C. ; Cameron, Lisa ; Perlman, Z. ; Ohi, Ryoma ; Desai, Ankur R. ; Salmon, Edward D. ; Kapoor, Tarun M.
    We investigated the mechanism by which meiotic spindles become bipolar and the correlation between bipolarity and poleward flux, using Xenopus egg extracts. By speckle microscopy and computational alignment, we find that monopolar sperm asters do not show evidence for flux, partially contradicting previous work. We account for the discrepancy by describing spontaneous bipolarization of sperm asters that was missed previously. During spontaneous bipolarization, onset of flux correlated with onset of bipolarity, implying that antiparallel microtubule organization may be required for flux. Using a probe for TPX2 in addition to tubulin, we describe two pathways that lead to spontaneous bipolarization, new pole assembly near chromatin, and pole splitting. By inhibiting the Ran pathway with excess importin-alpha, we establish a role for chromatin-derived, antiparallel overlap bundles in generating the sliding force for flux, and we examine these bundles by electron microscopy. Our results highlight the importance of two processes, chromatin-initiated microtubule nucleation, and sliding forces generated between antiparallel microtubules, in self-organization of spindle bipolarity and poleward flux.
  • Preprint
    Chromosomes can congress to the metaphase plate before biorientation
    ( 2005-12-09) Kapoor, Tarun M. ; Lampson, Michael A. ; Hergert, Polla ; Cameron, Lisa ; Cimini, Daniela ; Salmon, Edward D. ; McEwen, Bruce F. ; Khodjakov, Alexey
    The stable propagation of genetic material during cell division depends on the congression of chromosomes to the spindle equator before the cell initiates anaphase. It is generally assumed that congression requires that chromosomes are connected to the opposite poles of the bipolar spindle (i.e., “bi-oriented”). We found that chromosomes can congress before becoming bioriented. By combining the use of reversible chemical inhibitors, live-cell light microscopy and correlative electron microscopy, we found that mono-oriented chromosomes could glide towards the spindle equator alongside kinetochore fibers attached to other already bi-oriented chromosomes. This congression mechanism depended on the kinetochore-associated plus enddirected microtubule motor CENP-E (kinesin-7).