Cell Biology

One for You, Two for Me

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Science  17 Apr 2009:
Vol. 324, Issue 5925, pp. 315
DOI: 10.1126/science.324.5925.315b

Asymmetric cell division, wherein the daughter cell receives an unequal set of contents from the dividing mother cell, drives the formation of the many and diverse cell lineages that populate multicellular organisms. The single-celled yeast Saccharomyces cerevisiae also undergoes asymmetric cell divisions to produce so-called mother and daughter cells, but as this occurs at every cell division, there are no obviously distinct cell lineages formed, as is true for many unicellular organisms. However, a closer look at the way yeast proteins are segregated during meiosis reveals a rather different outcome.

Thorpe et al. have fluorescently tagged a number of proteins from the kinetochore (the molecular machine that links the chromosomes to the spindle in dividing cells and thus ensures their proper segregation) and find that they segregate asymmetrically at the first meiotic division, forming the haploid spore, and also in subsequent divisions, so that they are preferentially retained in the mother cell lineage derived from the spore. These same proteins are symmetrically distributed between other dividing “cell types,” and other proteins that are not part of the kinetochore do not show a similar asymmetry. The unequal segregation of the kinetochores may allow for the non-random segregation of sister chromatids, which would thereby maintain an “immortal” DNA strand, or of the centromeric DNA to which the kinetochores bind, which could drive the evolution of the centromeres. — GR

Proc. Natl. Acad. Sci. U.S.A. 106, 10.1073/pnas.0811248106 (2009).

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