Study finds that toothed whales have been lacking important antiviral genes for several million years -- a surprising discovery, since all 56 other sequenced mammals in the study possess these genes to fight off viruses like HIV, measles and flu
The basic role of Mx genes is to make proteins that fight viral infections such as HIV, measles and flu.
'We compared the whole-genome sequence of four toothed whales, a baleen whale and dozens of related mammals like cows and humans,' said Gill Bejerano, Ph.D., associate professor of developmental biology. 'When we looked carefully at the genome sequences, it was very clear that the Mx genes are completely messed up only in the toothed whales.'
The investigators were particularly intrigued by the genomic difference observed between the toothed and baleen whales, because they share a common ancestor. Instead of teeth, baleen whales have baleen plates, which they use to filter food from water.
Lost millions of years ago
'The simplest, most likely scenario is that the common ancestor of the toothed whales lost both Mx genes shortly after the baleens and toothed whales split about 33-37 million years ago,' Bejerano said. 'It's tempting to think that this common ancestor was subjected to a very nasty virus that was exploiting the Mx1 and Mx2 genes. Their option was to lose both genes or die. We can't know for sure, but it's a tempting hypothesis based on how some viruses seem to exploit Mx genes today.'
'It's likely that the toothed whales' immune system is very different from ours,' Bejerano said. 'I think this will open up very exciting research avenues, either to better protect the compromised whales, or to study their different viral defenses, and someday add them to our own arsenal. We're putting the genomic discovery out there, and we hope immunologists will follow up on it.