A major step in the development of the vertebrate embryo - the establishment of a back that morphs into a brain, spinal cord and muscles - turns out to be so important that the body uses at least three signals to make sure it happens properly. The discovery, reported this month in the journal Developmental Cell by researchers at the University of California, Berkeley, finally explains an 80-year-old observation that revolutionized the way biologists think about embryonic and fetal development and set the stage for the stem cell debate. That 1924 observation in newts by Hans Spemann and Hilde Mangold earned Spemann the Nobel Prize in 1935 and generated the notion that embryonic cells don’t know what they’ll become until they get the proper signal. This concept is at the root of today’s excitement over embryonic stem cells, which are basically naïve cells that, theoretically, can be stimulated to become any tissue of the body. In fact, the proteins normally used by the embryo have recently been put to use in embryonic stem cell work. Noggin, one of the proteins isolated by the UC Berkeley research group, has been used in cultures to maintain the growth of neural stem cells. The new UC Berkeley experiments, on frogs, show that some steps in early embryonic development are so critical that many overlapping signals are needed to ensure that cells go down the right path. The formation of the back and belly is a milestone for frogs as well as for humans and other vertebrates, occurring as it does at the beginning of the process of gastrulation, which sees front and back, head and tail, left and right established and the first appearance of a recognizable body plan. If this step fails, the embryo eventually dies.
