Polarized Myosin Produces Unequal-Size Daughters During Asymmetric Cell Division

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Science  29 Oct 2010:
Vol. 330, Issue 6004, pp. 677-680
DOI: 10.1126/science.1196112

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Daughter Diversity

Asymmetric cell division generates cell diversity and maintains tissue homeostasis. In early Caenorhabditis elegans embryos, the mitotic spindle is pulled toward one side of the cell by the molecular motor, dynein, and the cell divides into two unequally sized daughters. However, other types of asymmetric cell divisions (for example, in Drosophila neuroblasts) start with a centrally localized spindle. In this latter case, the mechanism by which two differently sized daughters are created is not understood. Ou et al. (p. 677, published online 30 September; see the Perspective by Grill) studied asymmetric cell divisions in the Q neuroblast lineage during C. elegans development and found that when the spindle was centred, myosin II accumulated at higher levels on the side of what will become the smaller daughter cell, giving rise to asymmetric myosin-based contractile forces acting on the membrane.


Asymmetric positioning of the mitotic spindle before cytokinesis can produce different-sized daughter cells that have distinct fates. Here, we found an asymmetric division in the Caenorhabditis elegans Q neuroblast lineage that began with a centered spindle but generated different-sized daughters, the smaller (anterior) of which underwent apoptosis. During this division, more myosin II accumulated anteriorly, suggesting that asymmetric contractile forces might produce different-sized daughters. Indeed, partial inactivation of anterior myosin by chromophore-assisted laser inactivation created a more symmetric division and allowed the survival and differentiation of the anterior daughter. Thus, the balance of myosin activity on the two sides of a dividing cell can govern the size and fate of the daughters.

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