Early in the life of every vertebrate embryo, be it human or hamster, there is a moment when the heart comes together -- literally. Scientists at the University of California, San Francisco have discovered a molecule that directs the two halves of the primordial heart to join as one.
Under the molecule's influence, separate tubes of the would-be heart -- primordial heart buds, essentially -- migrate toward each other from opposite sides of the embryo, the researchers found. As the two halves join, the rudimentary heart begins to beat.
The discovery is based on studies of zebrafish, tiny creatures which are utterly transparent as embryos. Many pivotal early changes that take place in the human embryo can be witnessed in zebrafish as if they were unfolding in a test tube. The fish is also fairly easy to study genetically.
The research, published in the July 13 issue of the journal Nature, shows that the normal union of the two heart tubes in the zebrafish embryo requires the presence of S1P, a molecule already known to be involved with cell proliferation and survival. S1P, an abbreviation for sphingosine 1-phosphate, is also active during wound healing, and the researchers suspect that its capacity to draw cells together is crucial there as well.
The heart buds join to form the zebrafish heart 22 hours into the embryo's life, and the heart begins beating soon thereafter. In the mouse embryo, the crucial union that will produce the heart occurs on the eighth day of development, and in human embryos, the heart forms and begins beating at three weeks, says Didier Stainier, PhD, UCSF associate professor of biochemistry and biophysics and senior author of the Nature study.
"S1P is a very old molecule," Stainier says. "It is present in organisms as distant as yeast and humans, and it appears to have been used over and over again throughout evolution for different roles: for cell proliferation, for wound healing, and now as we ha
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Contact: Wallace Ravven
wravven@pubaff.ucsf.edu
415-476-2557
University of California - San Francisco
11-Jul-2000