Evolution in reverse?

[darkangel199]

Geneticists are becoming so proficient that they can not only show evolution in action – they can show it in reverse. The experimental success could suggest a new approach for gene therapy, the researchers say, though any applications are a long way off.

 

Many of the genes in humans and animals are descendants of ancient genes that have duplicated, mutated and changed their function. Petr Tvrdik and Mario Capecchi, at the University of Utah in Salt Lake City, US, have now managed to demonstrate this by recreating an ancient gene from two of its modern descendants.

 

Half a billion years ago, our ancestor’s genome quadrupled. With four copies of each gene suddenly competing for existence, genes had to find a function or be purged from the genome. The quadrupling meant that 13 Hox genes, which control the development of body shape, became 52. The ones that did not mutate to do something useful were eventually lost, so today mammals have 39 Hox genes.

 

Tvrdik and Capecchi focused on two Hox genes, originally identical duplicates, that have evolved to perform different functions – a process of division of labour called subfunctionalisation. Hoxa1 controls brain stem development in the early embryo, and Hoxb1, working a bit later in development, directs nerve growth in an area of the brain that controls facial expression.

 

The two genes make the same protein, but in different places in the brain, and at different times. In other words, it is the regulatory sequence that differs, not the protein-coding sequence.

Dice and splice

 

To reconstruct the original Hox1 gene from which the two evolved, Tvrdik and Capecchi attached part of Hoxb1 – the regulatory sequence, which turns the gene on later in development – to the Hoxa1 gene. That way, one gene was able to do the job of two. Mice with the new Hox1 gene, but bred to lack their Hoxa1 and Hoxb1 genes, developed normally.

 

“We constructed a gene that is fairly similar to the ancestral Hox1 gene present in the vertebrate lineage half a billion years ago, before it became duplicated,” says Tvrdik.

 

The gene was inserted into a mouse embryonic stem cell, and then implanted into mouse surrogate mothers to produce mice which carry the new gene in their genome. The modified mice breed normally, and produce offspring with the new Hox1 gene.

More hurdles

 

“This is very elegant paper that reports what is effectively reverse evolution – reversal of the subfunctionalisation process that can occur following a gene duplication event,” says David Miller, a geneticist at James Cook University, Townsville, Australia.

 

The work suggests that duplicate genes have evolved to remain more similar than thought, which has implications for gene therapy if a broken gene could be replaced by another, Tvrdik says.

 

“Recruiting a gene to another function may prove to be more accessible, in specific instances,” he adds. But Tvrdik emphasises that there are many hurdles to overcome before this could happen – not least that it is not legal to alter human embryos, as the researchers did with mice in this study.

 

Journal reference: Developmental Cell (DOI: 10.1016/j.devcel.2006.06.016)

 

newscientist.com

[the tree]

Geneticists are becoming so proficient that they can not only show evolution in action – they can show it in reverse.

Sorry but what the hell? Evolution is change is evolution is change. Change going in the other direction is still change in the magnitute and is still evolution.

[Dr. Dalek]

Originally Posted by darkangel199

Geneticists are becoming so proficient that they can not only show evolution in action – they can show it in reverse

Sorry but what the hell? Evolution is change is evolution is change. Change going in the other direction is still change in the magnitude and is still evolution.

I agree the terminology is off a bit. Evolution is not one direction line and does not move in reverse or forward.

 

Though this is interesting. I've always wondered how one might study ancient genetics.

[darkangel199]

i posted the site, but i see it didnt come up. i know nothing about biology i just thought it was interesting to post. Perhaps i should have said Devolution? is that even a real word?

[Edtharan]

i posted the site, but i see it didnt come up. i know nothing about biology i just thought it was interesting to post. Perhaps i should have said Devolution? is that even a real word?

No devolution is not a word (this has been covered in another thread so I am not going to restart it here).

 

The best term for this would be "Genetic Engineering". They have genetically engineerd a gene sequance that is the same as an aincent gene. There has been no evolution, just Genetic Engineering (the closest you could come is "dramatic neutral mutation").

[Skye]

Sorry but what the hell? Evolution is change is evolution is change. Change going in the other direction is still change in the magnitute and is still evolution.

Well ok, evolution is obviously more than simply linear change, i.e. descent with modification. It's also lines splitting and changing independently each generation. If you reverse that process the lines merge, indicating (or assuming, depending the methodology) a common ancestor.

[lucaspa]

i posted the site, but i see it didnt come up. i know nothing about biology i just thought it was interesting to post. Perhaps i should have said Devolution? is that even a real word?

 

No. And the common usage wouldn't appy here anyway.

 

What the authors are doing is retracing evolution on a molecular level. NOT doing evolution in reverse.

 

The research is showing how things got to be the way there are today by means of evolution.

 

In this case, there was gene duplication -- a well-known phenomenon where the mistake in copying DNA results in 2 copies of the same gene. Now, while the original copy continues to do the job, the second copy can change without any penalty to the animal. After all, the original job is still covered.

 

In gene duplications known to date, the changes came in the coding region -- the areas that tell what the amino acid sequence of the protein is. The different types of collagen arose this way.

 

However, in this case the amino acid sequence of the protein for Hox1 is the same. What changed was the regulatory sequence. Remember, proteins are not turned on all the time in all cells. The regulatory sequence tells when to turn on the gene and have it make the protein. It is part of the gene but the DNA sequence that is the regulatory sequence lies in front of the sequence for the protein.

 

Here the regulatory sequence changed so that Hox1 is expressed at different times in different cells. Same protein doing 2 different things in the development of the central nervous system depending on which cells make it and when in development they make it. By making Hox1 later in development, it allows the new trait of facial expression.