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Asymmetric Cell Division

It is normally vitally important that cell division (cytokinesis) results in the division of the mother cell to produce two identical daughter cells with the same number of organelles such as mitochondria and in fact there are sophisticated mechanisms to ensure their equal division.  However, especially during development rapid changes to tissues result from unequal cell divisions, and from cell divisions where the plane of cell division is altered, both are forms of asymmetric cell division. The latter is considered first as it seems to be slightly less complex?

 

Figure 1.  One kind of asymmetry can results from rotation of the spindle pole so that the resulting cleavage furrow cuts across the cells in  different plane.  a. The mother cell rounds up. b. the nucleus divides in the normal fashion, redistributing the cytoplasmic contents equally c. On the subsequent division d, the spindle pole of one cell (the right cell) rotates e. so that after cell division, the right hand daughters are now stacked one on top of the other instead of side-by-side f. As the cells adopt their interface shapes once again, the difference in cell orientation is more clear g

The astral microtubules are thought to be pivotal (literally!) in the process whereby the spindle rotates, it is supposed that they interact with the cortical actin cytoskeleton under the plasma-membrane to move.  The details are sketchy at this stage however.

References:-

Alder, P. N. & Taylor, J. (2001) Asymmetric cell division: Plane but not simple. Curr. Biol. 11, R233-R236.

Badoual, M., Jülicher, F. & Prost, J. (2002) Bidirectional cooperative motion of molecular motors. PNAS. 99, 6696-6701.

Cleary, A. L. (2001) Plasma membrane-cell wall connections: roles in mitosis and cytokinesis revealed by plasmolysis of Tradescantia virginiana leaf epidermal cells. Protoplasma. 21, 21-34.

Gallagher, K. & Smith, L. G. (2000) Roles for polarity and nuclear determinants in specifying daughter cell fates after an asymmetric cell division in the maize leaf. Curr.Biol. 10, 1229-1232.

Le Borgne, R., Bellaiche, Y. & Schweisguth, F. (2002) Drosophila E-cadherin regulates the orientation of asymmetric cell division in the sensory organ lineage. Curr. Biol. 12, 95-104.

Kaltschmidt, J. A. & Brand, A. H. (2002) Asymmetric cell division:microtubule dynamics and spindle asymmetry. J.Cell Sci. 115, 2257-2264.

Knoblich, J. A. (2001) Asymmetric cell division during animal development. Nature Reviews Moleculer Cell Biology. 2, 11-20.

Waddle, J. A., Cooper, J. A. & Waterston, R. H. (1994) Transient localized accumulation of actin in Caenorhabditis elegans blastomeres with oriented asymmetric divisions. Development. 120, 2317-2328.

 
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