Sequencing of the bovine genome provides new information about mammalian evolution as well as cattle-specific biology and points the way to research that could result in more sustainable food production in a world challenged by global population growth, said a consortium of researchers led by the Baylor College of Medicine Human Genome Sequencing Center in two reports that appear today in the journal Science.
"The future challenge will be to explore the bovine genome sequence in greater depth to fully understand the genetic basis of the evolutionary success of ruminants as this will provide opportunities to address some of the crucial issues of the present time – efficient and sustainable food production for a rapidly increasing human population," said Dr. Richard Gibbs, director of the BCM Human Genome Sequencing Center and principal investigator on the project.
The cattle sequence took six years to complete, annotate and analyse and has involved over 300 scientists from 25 countries. The Bovine (Cow) Genome Sequencing Project sequenced the genome of a female Hereford cow.
"The mammals we have looked at previously have been laboratory animals and humans," said Dr. Kim C. Worley, associate professor in the sequencing centre and a corresponding author. "This is the first mammalian livestock animal we have studied."
The authors concluded that the bovine genome, consisting of at least 22,000 genes, is more similar to that of humans than that of mice or rats. They note that most cattle chromosomes correspond to part or all of human chromosomes, although the DNA is rearranged in some areas.
"During evolution, domesticated cattle and other ruminants diverged from a common ancestor that gave rise to humans about 95 million years ago, yet cattle and humans still share a high degree of conservation in the organization of their chromosome architectures, far more so than humans and mice do," said Dr. Harris Lewin, one of the lead analysts from the University of Illinois at Urbana-Champaign. "We were surprised to find that, like humans, duplicated segments appear to have played a major role in the rearrangements of chromosomes in the cattle lineage."
Some of these rearrangements appear important to cattle biology because they affect genes involved in immunity, lactation, metabolism and digestion. These changes could help explain the amazing ability of cattle to convert low-quality forage efficiently into energy-dense meat and milk, a fact that benefits humans.
One particular genetic rearrangement involves the histatherin gene in mammary tissue, which undergoes special regulation during lactation to produce a novel protein in milk that has anti-microbial activity. Other gene changes aid in the transfer of immunoglobulin G to milk and the subsequent transference of innate immunity to suckling calves from their dams.
The researchers said, "Observation suggests that species-specific changes in genome organisation and gene regulation may help tailor the functional components of milk to the specific needs of new-born mammals. They also add to the mounting evidence that milk contains 'innate immune' proteins that may be important for gut protection and gut development in the suckling young as well as the health of the mammary gland."
"More generally, it appears that the cow has significant rearrangements in many of its immune genes and enhanced innate immune defense capacity. This may be in response to increased risk of opportunistic infections at mucosal surfaces caused by the large number of microorganisms carried in the rumen (the largest of the four compartments that make up the bovine stomach)," said Dr. Ross Tellam of the Commonwealth Scientific and Industrial Research Organization of Australia.
Baylor College of Medicine
