DNA from invertebrates raises questions about existing models of evolution
Karina Denis, Nature (translation: Dikla Oren)
Research in corals suggests that ancient members of the animal kingdom slipped through the mud in the Precambrian era regarding a cache of shared genes with humans.
Surprisingly, we do not share many of these genes with creatures such as flies and worms, even though they evolved millions of years after corals, and this calls into question the validity of many studies that use these organisms as a model in studies to decipher the evolution of the human genome.
This study, published in this week's issue of Current Biology, examined about 1,300 gene sequences, which are expressed in the coral Acropora millepora (Acropora millepora), and found that about 500 sequences matched a database of genes. These sequences, called expressed sequence labels, represent individual genes, different parts of the same gene or expressed parts of the DNA, which do not contribute to the coding of a gene.
Of these, 90% were found in humans and about 10% were found in humans but not in the fruit fly Drosophila melanogaster or the nematode worm Cahenorhabditis elegans. The findings suggest that genes, which until now were thought to be unique to invertebrates, may have much earlier origins and were lost during the evolution of flies and worms.
"The assumption was that corals would lack the genes found in more advanced animals," says Robert Saint of the Australian National University in Canberra, one of the authors of the paper. Instead, they were surprised to find genes similar to those that contribute to the specialized tissues of vertebrate nervous systems, even though corals have a simple neural network.
"There are important scientific questions that we need to ask with the help of the coral system, which will 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 paper.
The idea that genes that until now were considered "innovations of vertebrates" might have evolved before the vertebrates themselves is not new. Alejandro Sánchez Alvarado, a developmental biologist at the University of Utah, had already found genes in the flatworm Shmidtea mediterrenea that were thought to be genes that evolved in vertebrates.
The idea that some animals may shed their genes as they develop, however, 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 Cal Institute of Technology in Pasadena.
The significance of the findings is that although the fly and worm models are effective for investigating gene functions in development and cellular processes, their value for research on the evolution of human genes may be limited. "We have to look at the genomes of many other animals, which have not undergone a process of gene loss at this level, to understand the evolution and roles of human genes, and how they create complexity," says Sánchez Alvarado.
