Like other organisms, the genomes of birds are riddled with DNA sequences from retroviruses. A study mBio this week examined the genomes of three species of birds for these proviruses and followed the expression of genes during development. What role these viral proteins might play in bird biology is not yet known, but in chickens, a surprising 20% of proviruses are translated during embryo development.
All genomes are cobbled together works-in-progress. Scientists have long known that the human genome, for example, is not all human: like most every other genome studied to date, a good chunk of the DNA we call “human” is actually made up of proviruses, sequences that retroviruses have deposited there to take advantage of the cell’s ability to copy DNA and translate that DNA into working proteins. These proviruses can either be inherited in the DNA we get from our parents (they’re called “endogenous retroviruses”), or they can be picked up during our lifetime (called “exogenous retroviruses”).
Bird genomes, too, contain proviruses, but the number and character of these viral sequences have not been studied in detail. The authors of the paper in mBio examined the genomes of the chicken, turkey, and zebra finch to learn more about the evolution of the viruses and of the birds themselves.
Stepher Goff of Columbia University edited the study for mBio. He says the numbers of proviruses the researchers found in bird genomes might surprise some people: the zebrafinch genome contained the most proviruses (1221), while the chicken (492) and turkey (150) carried fewer. “These are large numbers,” says Goff, “but they’re in accord with what we’ve seen in mammals.”
Click on the "Source" link above to read more on mBio's blog, mBiosphere.