Sea squirts, fish, and mammals don't look much alike, but glimpse at their embryos and you probably couldn't tell them apart. Among other similarities, all sport a tubelike structure stretching from head to tail—the notochord—that serves as a backbone, before being replaced by the spine. In the center of the notochord there are unusual cells filled with huge bubblelike structures called vacuoles that have puzzled scientists for decades. By making movies of living zebrafish embryos, researchers are now able to show how these notochord vacuoles start off as small bubbles, then fuse together and finally inflate until they fill up the cell (as seen above). Getting rid of the vacuoles using genetic tricks produced dwarf embryos that grew up to develop kinked spines, which would be the equivalent to human scoliosis. Scoliosis is a spine deformity of unknown cause that affects 2% of the adult population. In the new study, published today in The Journal of Cell Biology, the team suggests that the notochord vacuoles act as an inflatable scaffold to build a straight spine and that zebrafish could be a good model system to study human scoliosis.
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