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International Team Sequences Genomes of Two Ant Species

By Andrea Anderson

NEW YORK (GenomeWeb News) – In a paper appearing online today in Science, a collaborative research group involving investigators from the US and China report that they have sequenced the genomes of two ant species: Harpegnathos saltator, known as Jerdon's jumping ant, and the Florida carpenter ant, Camponotus floridanus.

By comparing genome and transcriptome patterns within and between the ant species, the team obtained clues about the genetic and epigenetic processes underlying diverse physical and behavioral features in the ants. And, they say, the findings may pave the way for future studies on everything from brain function and behavior to aging.

"Ant species have very diverse society organizations, and through sequencing-based research and analysis at DNA, RNA and epigenetic levels, we will have better understanding on the genetic basis of social behaviors and aging process," co-corresponding author Danny Reinberg, a biochemistry researcher at New York University, said in a statement.

Ant behavior and appearance can vary depending on their species and their place within ant social groups. For instance, the researchers noted, carpenter ants have strictly delineated social structure in which shorter-lived worker ants are further specialized into major or minor worker castes based on environmental cues.

These carpenter ant colonies typically die when longer-lived, reproductive queen ants die, they explained. Jumping ants, on the other hand, seem to have more primitive social structures. In this species, one or more worker ants can replace queens that die or are removed from the colony.

"[The two species] are very different," co-lead author Roberto Bonasio, a post-doctoral researcher in Reinberg's NYU lab, told GenomeWeb Daily News, explaining that while both species have societies and queens, they seem to be at opposite ends of the ant spectrum in terms of how these societies are organized.

Because ants from various castes within each species share the same genome but have distinct appearances, reproductive potential, and roles in the colony, he and his co-workers explained, comparing these castes to one another provides a window into the epigenetic processes that govern features such as behavior, brain, function, and aging — insights they say could ultimately provide clues about human biology, as well.

"Since every ant in the colony starts with the same genetic information, the different neuronal connections that specify the behavior appropriate for each social rank must be controlled by epigenetic mechanisms," Reinberg said in a statement.

For the current study, collaborators at the Beijing Genomic Institute-Shenzhen used the Illumina Genome Analyzer to sequence the 238 million base carpenter ant genome and the 297 million base pair jumping ant genome to about 100 times coverage each. The sequences generated cover an estimated 90 percent of each genome. The researchers also used RNA sequencing to assess expression patterns within and between the two species.

Their analyses turned up an estimated 17,064 genes in the carpenter ant genome and about 18,564 genes in the jumping ant genome. Most of these predicted genes were shared between both genomes, the team reported, while roughly 20 percent showed up in just one of the species.

When they compared the genomes with those of other organisms, they found that roughly two-thirds of ant genes are conserved within insects, while a third are shared with vertebrates, including humans.

Among the genes found in ant genomes alone, researchers found an over-representation of genes thought to be involved in processes such as smell, chemical sensing, and detoxification.

They also saw expansions involving genes from a histone methyltransferase gene family known as SMYD. These methyltransferases may contribute to epigenetic processes, Bonasio noted, and seem to have been duplicated in other insect species as well. In addition, the team's results suggest specific SMYD histone methyltransferases are differentially expressed based on ant caste in the jumping ant species.

The jumping ant workers that go on to adopt the functional role of queens also had higher expression of genes coding for the telomerase enzyme, which helps maintain telomere length and may contribute to lifespan, and sirtuin deacetylases, a group of enzymes implicated in age-related processes, were more highly expressed — perhaps reflecting queens' longevity.

"Some of the famous pathways that have been studied now for years that are linked to longevity and aging in humans — they seem to be at work in the ants," Bonasio said. "I think time will tell if these pathways are functioning in the same way in ants as they are in humans."

Other genes, including some miRNA genes and genes involved in brain and chemical communication-related processes seem to undergo caste-specific expression as well, the researchers noted.

When they compared methylation patterns in the two species, meanwhile, the team found that the relatively primitive jumping ants had lower methylation levels than the more complex carpenter ants, fueling speculation that such methylation discrepancies might explain some of the behavioral and social differences between the species.

"Maybe there is less DNA methylation in the primitive species because it's more flexible," Bonasio said. Still, he emphasized, more research is needed to determine whether that is the case.

Members of the team are currently doing follow-up research to address these and other questions. For instance, Bonasio noted, researchers are profiling methylation and histone modification patterns across the ant genomes in order to learn more epigenetic patterns and their regulation in these insects.

"I think, really, the discoveries will come once we are able to integrate different layers of information," Bonasio said.

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