Development

Counting Counts

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Science  22 Feb 2002:
Vol. 295, Issue 5559, pp. 1427
DOI: 10.1126/science.295.5559.1427a

The size and number of cells forming an individual organ or organism are tightly regulated. Tang et al. examined the formation of discrete-sized aggregates of the slime mold Dictyostelium discoideum under starvation conditions. In times of plenty, Dictyostelium cells live as single amoeboid cells in solution; however, starvation causes cells to club together into streams before forming fruiting bodies. When streaming, the cells secrete a complex of polypeptides known as counting factor (CF). High levels of CF indicate high cell densities and signal the cellular aggregation stream to break up into clumps of cells. By modeling cellular behavior in response to CF levels, the authors predicted that CF could either decrease cell-cell adhesion or increase cell motility. Direct analysis of cellular behavior confirmed that CF indeed affects both cellular characteristics. In particular, CF increases cell motility via effects on actin polymerization and myosin distribution. — SMH

Proc. Natl. Acad. Sci. U.S.A.99, 1371 (2002).

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