Animals as varied as grasshoppers and mice build their bodies by assembling repetitive pieces during embryonic development. A new study reveals that this process may have evolved long ago, as it shows that embryos from an ancient spider develop just like those of vertebrate animals.
Segmentation is widespread among vertebrates and other organisms. A few species, however, fruit flies in particular, don't seem to rely on it for early development. That's prompted researchers to speculate that sometime in the distant past, arthropods (a group that includes spiders, beetles, and flies) and vertebrates evolved separate ways to build their bodies. In recent years, scientists have found that in vertebrates, including mammals, the earliest stages of segmentation are governed by a key set of genes, headed up by the so-called Notch gene.
Michael Schoppmeier of the University of Cologne in Köln, Germany, and his colleagues were interested to see how Notch works in Cupiennius salei, a Central American hunting spider that dates back roughly 500 million years. They turned to RNA interference (RNAi), a technique that uses short stretches of RNA molecules to turn off certain genes. Using RNAi, the group switched off Notch in the spider embryos. They found that the Notch-deficient embryos were disorganized and malformed. Furthermore, eliminating a number of the genes known to work in the same gene pathway as Notch created similar chaotic patterns in the embryos, they report in the 18 June issue of Nature.
"This is an exciting finding, because it indicates that the molecular mechanisms underlying the segmentation clock are really quite ancient," says David Turner, a neurobiologist at the University of Michigan, Ann Arbor, who studies Notch in vertebrates. Schoppmeier and his colleagues are now trying to determine whether Notch and related genes turn on and off in the same fashion in early spider embryos as they do in vertebrates.