Some genes 'foreign' in origin and not from our ancestors

http://www.eurekalert.org/pub_releases/2015-03/bc-sg031015.php

Public Release: 12-Mar-2015
BioMed Central

Many animals, including humans, acquired essential 'foreign' genes from microorganisms co-habiting their environment in ancient times, according to research published in the open access journal Genome Biology. The study challenges conventional views that animal evolution relies solely on genes passed down through ancestral lines, suggesting that, at least in some lineages, the process is still ongoing.

The transfer of genes between organisms living in the same environment is known as horizontal gene transfer (HGT). It is well known in single-celled organisms and thought to be an important process that explains how quickly bacteria evolve, for example, resistance to antibiotics.

HGT is thought to play an important role in the evolution of some animals, including nematode worms which have acquired genes from microorganisms and plants, and some beetles that gained bacterial genes to produce enzymes for digesting coffee berries. However, the idea that HGT occurs in more complex animals, such as humans, rather than them solely gaining genes directly from ancestors, has been widely debated and contested.

Lead author Alastair Crisp from the University of Cambridge, UK, said: "This is the first study to show how widely horizontal gene transfer (HGT) occurs in animals, including humans, giving rise to tens or hundreds of active 'foreign' genes. Surprisingly, far from being a rare occurrence, it appears that HGT has contributed to the evolution of many, perhaps all, animals and that the process is ongoing, meaning that we may need to re-evaluate how we think about evolution."

•••••

The team were able to identify the likely class of organisms the transferred genes came from. Bacteria and protists, another class of microorganisms, were the most common donors in all species studied. They also identified HGT from viruses, which was responsible for up to 50 more foreign genes in primates.

Some genes were identified as having originated from fungi. This explains why some previous studies, which only focused on bacteria as the source of HGT, originally rejected the idea that these genes were 'foreign' in origin.

The majority of HGT in primates was found to be ancient, occurring sometime between the common ancestor of Chordata and the common ancestor of the primates.

The authors say that their analysis probably underestimates the true extent of HGT in animals and that direct HGT between complex multicellular organisms is also plausible, and already known in some host-parasite relationships.

•••••