Evans and colleagues from Canada, Argentina, and the United States report evidence that the huge genome of the red vizcacha rat Tympanoctomys barrerae – the largest of all mammals – expanded due to the accumulation of repetitive DNA

Evans and colleagues from Canada, Argentina, and the U.S. report evidence that the huge genome of the red vizcacha rat – the largest of all mammals – expanded due to the accumulation of repetitive DNA. Understanding that process may lead to greater understanding of the evolution of the human genome
Photo Credit: Andrea Tarquino

How study of a rare rat genome may relate to humans

The study involves an obscure little rodent living in the deserts of Argentina.

Though obscure, the rat is unique in the world. It seems to be the only mammal that has undergone a huge genome expansion resulting in a larger genome than humans, much, much larger in fact.

Ben Evans (PhD) is the lead author of a study of the red vizcacha rat. He is a professor in the biology department at McMaster University in Hamilton Ontario

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Ben Evans (PhD) Biology professor, McMaster University.
Ben Evans (PhD) Biology professor, McMaster University. © supplied

Professor Evans says this rather ordinary looking rodent has a genome about 2.6 times that of humans. It is the largest mammalian genome known. The genome represents the complete set of DNA.

The study of this rather unique animal is a collaborative international effort involving researchers from Canada, the U.S., and Argentina.

It was published in the journal  Genome Biology and Evolution under the title “ Evolution of the largest Mammalian Genome” (open access HERE)

What is also interesting Evans says, is that a close relative to the red vizcacha rat, the mountain vizcacha rat, has a genome about half the size of its cousin.

The harsh environment of the vizcacha rat in Argentina’s desert badlands
The harsh environment of the vizcacha rat in Argentina’s desert badlands © Ben Evans

What he and colleagues are studying is how and why this relatively rapid increase in the genome occurred, and in such a short time span in evolutionary terms.

 Setting a trap at the entrance to a rat hole
Setting a trap at the entrance to a rat hole © Ben Evans

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Samples of the animal’s DNA will be taken for analysis to better understand the evolution of its genome which may have information relative to human genome development
Samples of the animal’s DNA will be taken for analysis to better understand the evolution of its genome which may have information relative to human genome development © B Evans

It may have some role in the animal’s tolerance for an extremely salty diet, one which it’s cousin, the mountain vizcacha, cannot tolerate.

Plant of the genus Atriplex which is very saline. There are even salt grains on the leaves, giving them a whitish hue. The red vizcacha rat specializes on this species. It is not yet sure what role the rat’s genome may or may not play in the rat’s ability to live on the high saline diet.
Plant of the genus Atriplex which is very saline. There are even salt grains on the leaves, giving them a whitish hue. The red vizcacha rat specializes on this species. It is not yet sure what role the rat’s genome may or may not play in the rat’s ability to live on the high saline diet. © B Evans

It has relevance to humans as he says at least 20 per cent of the human genome is redundant. He notes that the mechanism for expansion of repetitive DNA in the vizcacha is the same as in humans and contributes to the extra DNA.

Researchers in the Argentine desert: L-R: Ricardo Ojeda, Ben Evans, Agustina Ojeda, Nate Upham, Ben Furman.
Researchers in the Argentine desert: L-R: Ricardo Ojeda, Ben Evans, Agustina Ojeda, Nate Upham, Ben Furman. © suppllied

He says this may play a role in disease through the interruption of gene function.

He adds that they have a great deal more to learn as their study progresses.

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Posted in Animals, Health, International, Science and Technology

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