La Jolla, Calif.- Humans and other animals may appear to be symmetrical on the outside, but symmetry is only skin deep. Many body organs, such as the stomach, the heart and the liver, are tipped to the right or left side. So how does the developing embryo distinguish left from right? Salk scientists have now discovered that the foundations for the basic left-right body plan are laid by a microscopic 'pump' on the outer surface of the embryo's underside that wafts chemical messengers over to the left side of the body. This sets up a chemical concentration gradient that tells stem cells how and where to develop. The remarkable findings, including movie footage of the 'pump,' are published in the May 20th edition of the journal Cell.

Juan Carlos Izpisa Belmonte and his colleagues studied the ventral node, a small patch of specialized cells on the outer surface of the underside ('ventral' side) of early embryos in many animals. Each cell in the ventral node has a single, rapidly rotating thread (cilium) projecting from the cell surface. Belmonte and colleagues at the University of Tokyo in Japan had previously demonstrated that the ventral node and its rotating cilia influence the left-right body plan, but until now no-one knew the mechanisms involved.

In the current study, Belmonte's team compared the ventral node in embryos of mice, rabbits and fish, and discovered the same mechanism in all these animals: the rapid, clockwise rotation of the whip-like cilia was actively moving fluid from the right side to the left side of the developing embryo.

The Salk scientists were intrigued by the finding because the forest of rotating cilia were more likely to create a whirlpool than a river. "The unidirectional flow produced by the rotation-like movement of the cilia required a specific mechanism because a simple circling movement would have, logically, just produced a vortex," said Belmonte.

Over the next three years, using a combination of
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Contact: Cathy Yarbrough
yarbrough@salk.edu
858-453-4100 x1290
Salk Institute
19-May-2005

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