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© The Rockefeller University Press, 0021-9525/2001//397 $5.00
The Journal of Cell Biology, Volume 153, Number 2, , 2001 397-412

A Mechanism for Nuclear Positioning in Fission Yeast Based on Microtubule Pushing

^a Department of Microbiology, Columbia University, New York, New York 10032
^b Long Island University, Department of Biology, Brooklyn, New York 11201
^c Institut Curie, Paris, Cedex 75005, France
^d Marine Biological Laboratory, Woods Hole, Massachusetts 02543
Columbia University, 701 W. 168th St., Rm. 1404, New York, NY 10032.(212) 305-1468(212) 305-3930

pt143{at}columbia.edu

The correct positioning of the nucleus is often important in defining the spatial organization of the cell, for example, in determining the cell division plane. In interphase Schizosaccharomyces pombe cells, the nucleus is positioned in the middle of the cylindrical cell in an active microtubule (MT)-dependent process. Here, we used green fluorescent protein markers to examine the dynamics of MTs, spindle pole body, and the nuclear envelope in living cells. We find that interphase MTs are organized in three to four antiparallel MT bundles arranged along the long axis of the cell, with MT plus ends facing both the cell tips and minus ends near the middle of the cell. The MT bundles are organized from medial MT-organizing centers that may function as nuclear attachment sites. When MTs grow to the cell tips, they exert transient forces produced by plus end MT polymerization that push the nucleus. After an average of 1.5 min of growth at the cell tip, MT plus ends exhibit catastrophe and shrink back to the nuclear region before growing back to the cell tip. Computer modeling suggests that a balance of these pushing MT forces can provide a mechanism to position the nucleus at the middle of the cell.

Key Words: nuclear positioning • microtubule dynamics • microtubule-organizing center • green fluorescent protein • Schizosaccharomyces pombe

© 2001 The Rockefeller University Press

Abbreviations used in this paper: GFP, green fluorescent protein; iMTOC, interphase MTOC; MBL, methyl-2-benzimidazole-carbamate; MT, microtubule; MTOC, MT-organizing center; SPB, spindle pole body; TBZ, thiabendazole.

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