Carpenter ants

In nature, carpenter ants in the same colony vary dramatically in size even though they are genetically very similar or identical to each other. Canadian researchers found that they could directly manipulate the ants' size by turning up or down a particular growth gene. (Mélanie Couture and Dominic Ouellette/McGill University)

Genetically identical carpenter ants can be raised to be dwarfs or giants by tuning up or down a single gene that controls their growth – a discovery that seems to reveal how nurture and nature interact to control variable traits like height, weight and intelligence and cancer susceptibility.

By tuning up or down the gene called Egfr – which is found in a huge range of organisms, including humans – scientists at McGill University in Montreal found they could double or halve the size of the ants. The study was carried out on ants that were either genetically identical or as genetically similar as human siblings.

"The effect was quite dramatic," said Ehab Abouheif, a McGill University biology professor who co-authored the paper published today in Nature Communications. He co-led the research with McGill University pharmacology professor Moshe Szyf.

The researchers turned the genes up or down using drugs that affected the methylation of DNA – chemical markings that are known to increase or decrease gene activity or expression. 

"Methylation coats genes a whole bunch or a little less," said Abouheif. "That acts like a dial."

The turning up or down of genes this way is called epigenetics.

Methylation is known to be affected by environmental factors such as stress.

Previous research had shown that DNA methylation could turn on or off certain traits in animals such as mice and insects. Abouheif and his colleagues wanted to know how it would affect traits like size that naturally have a huge range of variation.

Traditionally, he said, scientists had thought such traits were controlled by the interaction of large number of genes.

Single gene has huge influence

But the results of the new study suggest that in fact, they're controlled by the environment's effect on a single gene that may influence other genes.

Abouheif said he was surprised a single gene could explain so much. "That's the really amazing thing."

In nature, carpenter ants in the same colony vary dramatically in size even though they are genetically very similar or identical to each other. Ants of different sizes do different jobs within their colony.

Abouheif and his team examined the ants' DNA and found their sizes were closely related to the amount of methylation on the Egfr gene.

"What was important about that gene is… when we saw a 10 per cent change in size, we saw a 10 per cent change in DNA methylation of that particular gene. When we saw a 20 per cent change in size, we saw a 20 per cent change in methylation as well," said Sebastian Alvarado, co-lead author of the paper, in a video posted on YouTube explaining the research he did as a grad student at McGill. The other co-lead author of the paper was Rajendhran Rajakumar.

The researchers decided to try manipulate the methylation of the ants' DNA while they were young and growing by treating them with certain drugs.

"We diluted it and we sort of poured it on them," said Abouheif, who said it was then absorbed through their skin.

Some ants were treated with the drug 5-AZA-dCytidine, which turned methylation down. That increased growth. Others were treated with S-adenosyl methionine, also known as folate (and is found naturally in food that humans eat), which turned methylation up. That decreased growth.

Cancer link

Abouheif said a similar mechanism may turn up or down the same gene in other organisms such as humans.

"It's associated with a crapload of cancers," he added.

Cancers can arise when something in regulation of growth goes wrong, and an environmental mechanisms to control growth is sought for its potential to prevent things from going wrong.

"The potential there is enormous," said Abouheif.

Similarly, being able to control growth this way might be handy in agriculture, he added.

But he noted that the work is still in its very early stages.

He said his team is now trying to pin down exactly what environmental influence changes the methylation of the growth gene in ants. Based on previous studies, they suspect it is the amount of food the ants are given.

The researchers are also trying to figure out what other genes are affected by drugs that turn up or down methylation.