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NEWS OF THE WEEK EVOLUTION 1612 18 DECEMBER 2009 VOL 326 SCIENCE Published by AAAS www.sciencemag.org CREDIT: MARK REBEIZ ET AL., SCIENCE Almost 3 years ago, biologists got University of Wisconsin, Madiinto a tussle over what drives morson, and their colleagues followed phological evolution: changes in up on work into why the normally the protein-coding portions of yellow abdomens of fruit flies genes or changes in the DNA (Drosophila melanogaster) have regions that regulate gene activity. become dark in some African At the time, some researchers felt populations living at high elevathere was little hard evidence to tions. Earlier work done by collabsupport the idea that regulatory orators John Pool of the Univerchanges were indeed important sity of California, Berkeley, and (Science, 8 August 2008, p. 760). Charles Aquadro of Cornell UniNow, on page 1663 and in last versity suggested that this color week’s Science Express (www. change was due to a change in the sciencemag.org/cgi/content/ activity of a gene called ebony. abstract/science.1182213), two The new work narrows down teams not only independently the cause to an enhancer upstream report that changes in regulatory Color coordinated. In Africa, lowland fruit flies are light-colored, whereas those of the gene. By dissecting the DNA were responsible for an adap- at high altitudes are dark, all because of a change in gene regulation. function of this region in different tation in natural populations of fish Drosophila populations, ones and insects, but each group has also pieced in both fish types. But it’s active in the pelvic with either dark or light abdomens, the together details of the underlying genetic alter- region of the saltwater animals and not in the researchers identified five mutations that ations in those animals. “They provide beauti- freshwater ones, Kingsley’s team found. Yet reduced ebony expression to varying degrees. ful and convincing examples of how [certain] the gene’s coding region is virtually unchanged Three of those mutations are present in regulatory elements can be lost or modified to between fresh- and saltwater fish, suggesting Drosophila with light abdomens, but the reduce [gene] expression, ultimately causing regulatory DNA is the difference. dark flies from high altitudes also have two morphological change,” says Hopi Hoekstra, The new work confirms that suspicion. newer mutations. These two have the biggest an evolutionary biologist at Harvard University When Kingsley, his graduate student Yingguang effects on squelching ebony expression, but and one of the chief skeptics. Frank Chan, now at the Max Planck Institute all five mutations combine to create the full In one case, the same piece of regulatory for Evolutionary Biology in Plön, Germany, color change. DNA was lost in different freshwater fish and their colleagues studied fish with and The work “leads to two very important populations, each time causing the loss of without a pelvis, they determined that DNA conclusions about classic evolutionary pelvic spines. In the other case, the darkening upstream of Pitx1 was responsible for genetic questions,” says William Cresko, an of a fruit fly took place through an accumula- silencing the gene. They broke that DNA evolutionary biologist at the University of tion of small mutations in regulatory DNA. into fragments and determined exactly Oregon, Eugene. One is that a “big” evoluTaken together with other discoveries of non- which piece, an enhancer called Pel, turned tionary step—a color change—actually can coding regions involved in evolution, “there Pitx1 on in the pelvis. When the researchers come about because of several little steps: is broad support now” that changes in regula- compared the sequence of Pel in saltwater multiple mutations in the enhancer. Secondly, tory DNA can generate morphological varia- sticklebacks and freshwater ones from nine it shows that adaptive mutations sometimes tion, says Günter Wagner, an evolutionary different lakes, they found the latter popula- exist unnoticed in a population. developmental biologist at Yale University. tions each had various amounts of missing Others are also in hot pursuit of evolutionThe fish study took place at Stanford Uni- DNA bases in the enhancer region, includ- ary changes based on regulatory elements. versity, where David Kingsley has spent the ing an apparently key 488-base region that is Wittkopp is homing in on mutations in a regpast decade tracking down the genetic basis for absent in most of the lake fish. ulatory region that change body color why three-spined sticklebacks (Gasterosteus “The fact that multiple alleles, with unique between two closely related species of fruit aculeatus) that live in salt water have spines mutations, were observed is surprising and flies (Science, 23 October, p. 540). And jutting from their belly whereas some of their emphasizes the tinkering nature of the evo- Hoekstra’s group has a regulatory region in its freshwater counterparts do not. In salt water, lutionary process,” says Patricia Wittkopp, an sights that seems to underlie mouse color the pelvic spines help make the stickleback evolutionary biologist at the University of changes (Science, 28 August, p. 1095). But difficult for a predator to swallow, but the pro- Michigan, Ann Arbor. developing a broad understanding of the relatuberances become a hindrance in fresh water To conf irm Pel’s importance, the re- tive roles of shifts in gene regulation versus as they could serve as handholds onto which searchers added a saltwater stickleback’s ver- changes in the proteins encoded by genes dragonflies and other carnivorous insects grab. sion of the enhancer and Pitx1 to the fertilized “will require many more case studies from In 2004, Kingsley and his colleagues eggs of freshwater sticklebacks that don’t nor- across a wide array of taxa,” cautions Cresko. tracked the disappearance of the pelvis in mul- mally sport pelvic spines. The resulting trans- Given how much work the two new studies tiple populations of freshwater sticklebacks genic freshwater fry developed the structures. took, he adds, it may require a “quantum primarily to a gene called Pitx1. The gene is For the insect study, evolutionary biolo- leap” in technology for that to be possible. expressed during development in many places gists Sean Carroll and Mark Rebeiz of the –ELIZABETH PENNISI Downloaded from www.sciencemag.org on January 10, 2010 Spineless Fish and Dark Flies Prove Gene Regulation Crucial