The three proteins identified in the team's report are among at least five that block other signals to allow the back, or dorsal, structures to form. Thirteen years ago, Richard Harland, professor and chair of the Department of Molecular and Cell Biology at UC Berkeley, showed that injecting one of these factors, noggin, into the belly of an embryo caused surrounding tissues to develop into structures normally found on the back. Despite repeated attempts, however, no one could show that blocking signals like noggin did the opposite. In fact, blocking noggin and the other known factors seemed to have relatively little effect on the embryo, raising doubts about the natural role of these proteins in early development.
Now, using very young embryos of the laboratory frog Xenopus tropicalis, Khokha, Harland and their UC Berkeley colleagues were able to block three of the five factors at once, and this time found dramatic changes in the embryo.
"When we removed these signals, all the tissues that form on the back of the embryo - brain, spinal cord and muscles - were lost," Khokha said. "Not only were back tissues lost, but belly tissues were greatly expanded - the whole embryo became repatterned, so it's more belly-like than it is back-like. So, these signals are necessary for the pattern to occur properly."
"We first found these signals in 1992, and since then, we've figured out how they work. But because there are so many of them, it's been difficult to really nail down that they are essential," Harland said. "We've had to knock down three of them to prove that they're essential."
In the 1920s, working at the University of Freiburg in Germany, Spemann and his student Mangold found that a
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Contact: Robert Sanders
rsanders@berkeley.edu
510-643-6998
University of California - Berkeley
9-Mar-2005