PerspectiveDevelopmental Biology

Cilia Discern Left from Right

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Science  12 Oct 2012:
Vol. 338, Issue 6104, pp. 206-207
DOI: 10.1126/science.1230401

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Although the human body shows left-right (L-R) mirror symmetry when viewed externally, the placement and patterning of the internal organs and associated vasculature are strikingly asymmetrical. In the mammalian early embryo, L-R symmetry is broken by the action of rotating cilia—small hair-like protrusions on the surface of cells—in a pit-like structure called the node (see the figure).These cilia generate a unidirectional flow of fluid across the node from right to left (1). This nodal flow breaks L-R symmetry by driving asymmetries in gene expression and Ca2+ signaling in cells at the periphery of the node. On page 226 of this issue, Yoshiba et al. (2) reveal a mechanism by which the mouse embryo senses nodal flow.