Cell Biology

Moving Toward Asymmetry

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Science  02 Jan 2009:
Vol. 323, Issue 5910, pp. 16
DOI: 10.1126/science.323.5910.16a

Asymmetric division intrudes at various stages of development in order to generate daughter cells with distinctly different fates. An extreme instance occurs during oocyte maturation when the oocyte expels half of its chromosomal capital by packaging them into a small polar body, leaving behind the vastly larger haploid egg. To pull off this feat the oocyte needs to move its centrally located mitotic spindle to the cell periphery, in a process that relies on the actin cytoskeleton.

Schuh and Ellenberg describe the role played by actin by watching spindle relocation in real time in live mouse oocytes. The actin cytoskeleton undergoes constant remodeling that relies on the activity of an actin-nucleating protein, formin-2. In particular, actin (shown at right, green) in the vicinity of the spindle (red) showed net flux toward the spindle poles, whereas actin elsewhere in the cell did not perform concerted directional movements. This poleward flux became especially apparent as the spindle approached the cell cortex. Along with this recruitment of actin, the activated form of the actin motor myosin-2 was also observed to accumulate near the spindle pole-associated actin filaments. Inhibition of myosin-2 motor activity interfered with the movement of actin toward the spindle poles and with spindle movement toward the periphery. Thus, spindle relocation depends on the interaction between the mitotic spindle poles and the actin cytoskeleton, which promotes the relocation of the spindle to the cell periphery and allows for the asymmetric division that produces egg and polar body. — SMH

Curr. Biol. 18, 10.1016/j.cub.2008.11.022 (2008).

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