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Constant overlap: Scientists identify molecular machinery that maintains important feature of cell's spindle

Date:
August 12, 2010
Source:
European Molecular Biology Laboratory (EMBL)
Summary:
Scientists in Germany have uncovered the molecular mechanism that determines the size of anti-parallel microtubule overlaps in a cell's spindle. In a new study, they were able to reconstruct such overlaps in vitro, and identify two proteins which are sufficient to control the formation and size of this important spindle feature.

If both PRC1 and kinesin-4 are present (top image from video), microtubules (blue) grow only until their overlap (red/yellow) reaches a certain size, which then remains constant. But if only PRC1 is present, microtubule growth is not inhibited in the overlap region, which becomes bigger and bigger (second image from video).
Credit: EMBL/P. Bieling

During cell division, microtubules emanating from each of the spindle poles meet and overlap in the spindle's mid zone. Scientists at the European Molecular Biology Laboratory (EMBL) in Heidelberg, Germany, have uncovered the molecular mechanism that determines the extent of this overlap.

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In a study published in Cell, they were able to reconstruct such anti-parallel microtubule overlaps in vitro, and identify two proteins which are sufficient to control the formation and size of this important spindle feature.

Thomas Surrey and his group at EMBL found that one protein, PRC1, bundles together microtubules coming from opposite ends of the cell, attaching them to each other. It then recruits a second protein, a molecular motor from the kinesin-4 subfamily, increasing its concentration in the spindle mid zone. This motor walks along the overlapping microtubules like an officer on patrol, until it reaches one of the ends. When enough kinesin-4 molecules reach the end of the overlap, they inhibit the growth of microtubules there, thus keeping the overlap size constant without affecting microtubules elsewhere in the cell.

The spindle mid zone plays an important role not only in helping to align the chromosomes in metaphase, but also in the final stages of cell division, when it drives the physical separation of the two daughter-cells. But between these two stages, the two ends of the spindle must move away from each other, to drag half the genetic material to each side of the dividing cell. At this point, if PRC1 and kinesin-4 had stopped microtubule growth permanently in the central part of the spindle, the overlap would become smaller and smaller, until eventually the spindle itself would collapse, jeopardising cell division.

But Surrey and colleagues found that PRC1 and kinesin-4 control the overlap size in an adaptive manner. As the spindle stretches and the overlap between microtubules becomes smaller, the scientists posit, the inhibitory effect of kinesin-4 diminishes, allowing the microtubule ends to grow.

"Our findings show how molecules millionths of millimetres small can control the size of a structure about a thousand times larger than themselves," Surrey concludes: "they help us to understand the fundamentals of cell division."


Story Source:

The above story is based on materials provided by European Molecular Biology Laboratory (EMBL). Note: Materials may be edited for content and length.


Journal Reference:

  1. Bieling, P., Telley, I.A. & Surrey, T. A Minimal Midzone Protein Module Controls Formation and Length of Antiparallel Microtubule Overlaps. Cell, 2010; 142 (3): 420 DOI: 10.1016/j.cell.2010.06.033

Cite This Page:

European Molecular Biology Laboratory (EMBL). "Constant overlap: Scientists identify molecular machinery that maintains important feature of cell's spindle." ScienceDaily. ScienceDaily, 12 August 2010. <www.sciencedaily.com/releases/2010/08/100806080215.htm>.
European Molecular Biology Laboratory (EMBL). (2010, August 12). Constant overlap: Scientists identify molecular machinery that maintains important feature of cell's spindle. ScienceDaily. Retrieved November 28, 2014 from www.sciencedaily.com/releases/2010/08/100806080215.htm
European Molecular Biology Laboratory (EMBL). "Constant overlap: Scientists identify molecular machinery that maintains important feature of cell's spindle." ScienceDaily. www.sciencedaily.com/releases/2010/08/100806080215.htm (accessed November 28, 2014).

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