Coral reveals ancient origins of human genes

Nature Magazine ^ | 16 December 2003 | CARINA DENNIS

[PatrickHenry]

A study of coral suggests that ancient members of the animal kingdom slithered through the Precambrian mud with a hefty cache of genes in common with humans.

Surprisingly, many of these genes are not shared with creatures such as flies and worms, even though these animals evolved millions of years after coral. This calls into question some studies that use these model organisms to unravel the evolution of the human genome.

The investigation, published in this week's Current Biology¹, looked at some 1,300 gene sequences expressed in the coral Acropora millepora, and found that about 500 sequences had matches in gene databases. These sequences, called expressed sequence tags, represent either single genes, different pieces of the same gene, or expressed portions of DNA that do not contribute to a coding gene.

Of these, 90% were present in humans, and about 10% were found in humans but not in the fruitfly Drosophila melanogaster or the nematode worm Caenorhabditis elegans. This finding suggests that many genes thought to be vertebrate-specific may in fact have much older origins, and have been lost during the evolution of the fly and worm.

"The assumption was that coral would lack many of the genes found in higher animals," says Robert Saint of the Australian National University in Canberra, one of the study's authors. Instead, they were surprised to find genes similar to those that contribute to the specialized tissues of vertebrate nervous systems, even though coral has only a simple nerve net.

"There are important basic scientific questions that we need to ask using the coral system that should tell us about the evolution of developmental mechanisms in the animal kingdom," says David Miller, a molecular biologist at James Cook University in Townsville, Australia, and co-author of the study.

The idea that genes previously regarded as 'vertebrate innovations' may have evolved before vertebrates did isn't new. Alejandro Sánchez Alvarado, a developmental biologist at the University of Utah, previously found genes in the flatworm Schmidtea mediterranea that were thought to have evolved in vertebrates².

But the idea that some animals may discard genes as they become more sophisticated is still controversial. "We won't really know until we have more worm and insect genomes to compare," says developmental biologist Eric Davidson of the California Institute of Technology in Pasadena.

The finding means that although fly and worm models are useful for studying gene function in development and cellular processes, they may be of limited value in studies of the evolution of human genes. "We need to look at many other animal genomes that haven't undergone the same degree of gene loss to understand the evolution and function of human genes, and how they generate complexity," says Sánchez Alvarado.

[PatrickHenry]

The footnotes are found at the end of the original article. Underlining is not found in the original article (it's the work of your humble poster).

Why post this article? It's presumably evidence of genes skipping over intermediate species. Very curious stuff.

[PatrickHenry]

PING. [This ping list is for the evolution side of evolution threads, and sometimes for other science topics. FReepmail me to be added or dropped.]

[samtheman]

Flies and worms and other bugs do share a lot of genes involving the basic biochemistry of life. It's just that some of the morphology stuff got "dropped".

[RadioAstronomer]

Thanks for the ping. :-) Interesting.

[Right Wing Professor]

Why post this article? It's presumably evidence of genes skipping over intermediate species. Very curious stuff

No, it isn't evidence of that. Drosophila and Caenorhabditis are not our ancestors, and they're not intermediate species, they're way off on other branches of our family tree, branches that are likely at least 600 my long.

The common ancestor of corals and humans had the gene. That creature would also have been an ancestor of nematodes and arthropods. The gene was lost early in the lineage of nematodes and of arthropods, but retained in the primitive chordates. It's not the first example of this.

[Ff--150]

My great-great-great-great-great-great--etc.-etc. grampaw--Mr. Coral. No wonder I'm so abrasive???

[thinktwice]

"The world is so full of a number of things,
I'm sure we should all be as happy as kings."

Happy Thoughts by Robert Louis Stevenson

[Doctor Stochastic]

You could have entitled an article about coral Reefer Madness.

[PatrickHenry]

The gene was lost early in the lineage of nematodes and of arthropods, but retained in the primitive chordates. It's not the first example of this.

Oh. I was worried for a minute there that I might not be related to pond scum. It's comforting to know that my pedigree is intact.

[Papabear47]

Question.If a particular attribute begins to develop such as feathers on early reptiles does the gene responsible for the previous skin mutate or is it replaced by the new gene.

[John H K]

I dimly remember from a class in Oceanography that Tunicates were right on the human ancestral line - have they been sequenced? Should be closer than coral.

[RadioAstronomer]

If a particular attribute begins to develop such as feathers on early reptiles does the gene responsible for the previous skin mutate or is it replaced by the new gene

I have pinged a few folk who could better answer your question. I will still do a bit of research on the answer though. :-)

[LiteKeeper]

YEC SKEPTICAL INTREP

[RussianConservative]

Not intermediate if segment into basic family groups: vertabrets, invertabrets and crustation/exoskeletal creature.

[RussianConservative]

Put me on?

[4CJ]

My great-great-great-great-great-great--etc.-etc. grampaw--Mr. Coral. No wonder I'm so abrasive???

Nah, you're not abrasive. A little opinionated maybe. And maybe a little hard-headed. Well, maybe more than a little. Come to think of it, a whole lot more than a little.

And definately opinionated, I mean, every conversation we have, you have your opinion and never - never - deviate from it. So I'd have to say your're extremely opinionated and hard-headed. And definitely abrasive to boot.

;o)

[PatrickHenry]

Done.

[pabianice]

Bush did it.

[Gorjus]

does the gene responsible for the previous skin mutate or is it replaced by the new gene.

Short answer: Yes. Longer answer: It depends.

Wild Analogy: The gene sequence is like a computer code (okay, so that part is not so wild) but it's designed to run on a limited system. If you want to add a feature, you either need to modify an existing feature or delete it because there's only so much room for code. And so both of your options apply, sometimes both together. As time goes on, like computers, some better models are developed that can run larger and more complex codes. (And some creatures, like coral, don't make many modifications to their code, so they have unused bits hanging around that other creatures have had to replace or modify.)

Final observation: The way in which genes work is a lot more complex than the simple Mendeleev model. (Warning, anlogy switch coming) I think we're going to find that much of what we think of as genes are more analogous to letters than distinct blueprints for physical characteristics. As a whole, the letters form words and sentences, but the specific letters are be used in lots of places. Just because we find one word using that letter doesn't mean we understand the scope of uses for that letter.

[Alamo-Girl]

Thanks for the ping!