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The Backbone of Proper Development

Friday March 18, 2005

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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 occurs properly. 

New experiments on Xenopus tropicalis frogs finally explain an 80-year old observation that revolutionized the field of embryonic and fetal development.  Until now, scientists were not sure which of the signals expressed in development were responsible for ensuring 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.  It occurs at the beginning of the process of gastrulation, during which the front and back, head and tail, left and right are established, creating the first appearance of a recognizable body plan. If this step fails, the embryo will eventually die.

"Gastrulation and the process of defining your back-belly axis is such an important step that you actually have multiple proteins being expressed there, just in case one of them fails, the others can compensate," said lead author and UC Berkeley post-doctoral fellow Mustafa Khokha.  "Redundancy is designed to make the embryo robust, so as to avoid birth defects."

Khokha and his colleagues at UC Berkeley 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 re-patterned, so it's more belly-like than it is back-like. So, these signals are necessary for the pattern to occur properly."

The discovery was reported this month in the journal Developmental Cell.

                                                                                    -- Bjorn Carey

Credit: Harland lab/UC Berkeley

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