Science 27 October 2006:
Vol. 314. no. 5799, pp. 578 - 579
DOI: 10.1126/science.314.5799.578
Four years in the making, the 236-million-base genome of the European honey bee, Apis mellifera, proved tough to decipher. But the hard work paid off this week as 170 researchers rolled out their analysis of this fifth insect sequenced to date. "To have [this] genome laid out in some detail is a real step forward for our understanding of this part of the animal kingdom," says Francis Collins, director of the National Human Genome Research Institute in Bethesda, Maryland, which funded the sequencing work.
The honey bee genome, described in the 26 October issue of Nature, has inspired dozens of recent papers in several journals, including three this week in Science. The 10,157 genes identified so far contain clues about the social behavior, physiology, and evolution of the honey bee, as well as insights into other insects and even vertebrates. The sequence also promises to illuminate the genetic and neural basis of animal social behavior. "It's the understanding of behavior that's going to be the big payoff [of the honey bee genome]," predicts George Weinstock, the geneticist at Baylor College of Medicine in Houston, Texas, who led the sequencing effort.
Bee hives are organized around an egglaying queen tended by workers who, during their lifetime, make the transition from hive-bound duties, such as nursing larvae, to more far-ranging jobs such as foraging for food or defending the nest. With just a million neurons, the bee brain is relatively simple, yet these insects are sophisticated--for example, they use highly choreographed "dances" to communicate the location of nectar-laden flowers.
With the aid of the genome data, Gene Robinson, a neurobiologist at the University of Illinois, Urbana-Champaign (UIUC), has begun to tease apart the genetic and environmental components of the bee social structure and its related behaviors (Science, 10 October 2003, p. 296). Now, working with Charles Whitfield, a geneticist also at UIUC, Robinson has used microarrays to determine which of 5500 genes are active in young bees and which are affected by age-related changes in juvenile hormone, a key mediator of behavioral maturation. Those results appeared online 26 October in the Proceedings of the National Academy of Sciences (PNAS).
Two other studies, one reported in the same PNAS issue and another in Science, begin to address what turns the bee's behavioral genes on and off. On page 647, Robinson's UIUC colleague Saurabh Sinha has picked out some of the regulatory regions that control some 3219 genes in the bee's brain, including ones important for the development of foraging behavior. And on page 645, Ying Wang in Robinson's lab and their colleagues report that unlike other insects studied, the honey bee has a vertebrate-like set of enzymes needed to methylate genes, implying that methylation may be important in silencing genes in bees as well as in vertebrates, including humans. "For people interested in human behavior, their interest [in the honey bee] has just gotten supercharged," says Collins.
Meanwhile, evolutionary biologists are keen to compare the honey bee genome to those of the six-legged lab rat of the insect world--the fruit fly--the mosquito, and the silkworm. "We are poised to sketch out the beginnings of genomic evolution in the insects, a not-trivial slice of the diversity of life," says Brian Farrell, a Harvard entomologist at the Museum of Comparative Zoology in Cambridge, Massachusetts. Moreover, a new bee fossil found in 100-million-year-old amber, reported on page 614, should clarify how honey bees evolved from predatory wasps and became key pollinators. The fossil, and the pollen captured with it, are "enabling us to place a time frame on this genomic evolution," Farrell adds.
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Compared to the fruit fly and the mosquito, the honey bee has evolved at a glacial pace, Weinstock and colleagues report in the 26 October Nature paper. But compared to those two insects, certain gene families essential to the bee's social lifestyle have expanded in size. In the November issue of Genome Research, Hugh Robertson and Kevin Wanner of UIUC report about 165 odorant-receptor genes in the honey bee genome, more than double what Drosophila and Anopheles have. This expansion makes sense, says Robertson, given the bee's need to recognize kin and find suitable flowers. Honey bees also have multiple versions of a pigmentation gene, called yellow protein, that have been co-opted to make royal jelly, a nutrient-rich secretion that causes larvae to develop into queens, Ryszard Maleszka of Australian National University in Canberra and his group report in the same issue of Genome Research.
In a few respects, the honey bee shares more similarities with humans than with the other insects whose genomes have been sequenced. It retains some 700 genes found in other organisms, such as nematodes, yeast, or mammals, that the fruit fly and mosquito have lost. Those genes are presumably ancient, found in the common ancestor of all the creatures and then lost in a few lines. Take some of the genes that drive the biological clock behind circadian rhythms. The honey bee has several clock genes that closely resemble mammalian clock genes yet are missing in fruit flies, says Guy Bloch of The Hebrew University of Jerusalem, Israel. At the same time, the honey bee lacks two of the fruit fly's clock genes, says Bloch. Drosophila apparently grew to depend on one subset of an ancient cluster of clock genes, whereas bees and mammals depend on another.
Dozens of other findings have come out of this first round of exploration into the honey bee genome, says Weinstock. Still, he's most excited about the long-term effect of this massive endeavor. "It's very gratifying to see the biology coming alive right away. [but] it's more than just teasing the biology out," Weinstock says. "It's getting the whole community up to speed in genomics."