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April 23, 2009
UC DAVIS-LED RESEARCH CONSORTIUM EXPLORES MILK GENOME
In tandem with the publication of the entire cattle genome, a
consortium of researchers led by scientists at the University of
California, Davis, are unveiling the first comprehensive overview of
the portion of the genome, or entire collection of genes, responsible
for milk and milk production in cattle and six other species of
Findings from the study by the Bovine Lactation Genome Consortium
paint a vivid picture of the molecular evolution of milk and
lactation, and will be published in the April 24 issue of the online
journal Genome Biology.
The paper appears as a companion piece to the landmark sequencing of
the entire cattle genome, which will be published in two reports in
the April 24 issue of the journal Science. That announcement marks
the climax of a six-year effort to complete, analyze and interpret
the cattle genome. The massive project was carried out by a
collaborative of more than 300 scientists from 25 countries,
including the UC Davis researchers. It was coordinated by the Baylor
College of Medicine Human Genome Sequencing Center.
Data produced by the overall genome sequencing will enable
researchers to identify genetic variations in cattle that are
important not only for milk production and milk composition but also
for reproduction, feed efficiency, meat quality and disease
resistance. It will have direct application in helping to guide the
selection of high-performing individuals in cattle breeding programs.
"The sequencing of the cattle genome represents a breakthrough for
the study of milk and lactation," said Danielle Lemay, the lead
author on the milk genome study and a bioinformatician and nutrition
scientist in UC Davis' Department of Food Science and Technology.
"When paired with existing data, the bovine genome sequence is
something of a modern Rosetta stone, making it possible to identify
and interpret the significance of genes related to milk and
lactation," she said.
Researchers note that the genome sequence and the identification of
sequence variation will improve the accuracy and efficiency of
genetic selection in cattle by allowing the evaluation of an animal's
whole genome. The genome sequence also opens the door to the
identification and description of all cattle genes and to the
understanding of their function in relation to production traits.
This information will be valuable in improving the sustainability of
the dairy and beef cattle breeding systems.
The milk genome
The milk-genome researchers focused on cattle genes involved with
milk and the lactation process because of the unique role that milk
plays in the lives of cattle, humans and all other mammals.
"Milk uniquely informs us about nutrition because it is the only food
that has evolved specifically to nourish mammals," said UC Davis
professor and food scientist Bruce German.
"Because milk is produced for offspring at great physiological
expense to the mother, we can theorize that there are few superfluous
components in milk," he said. "Generation after generation, those
animals that are able to produce more nourishing milk perpetuate
their genes through the survival and reproductive success of their
In the companion paper on the milk genome, the researchers identified
197 milk-protein genes and more than 6,000 milk-production genes
within the overall cattle genome. They dramatically narrowed the
search for genes that affect milk traits by overlaying this data on
existing information regarding 238 DNA segments that are known to be
associated with particular traits.
"Overall, the findings of our study support the hypothesis that the
biological roots of milk production in mammals are quite ancient and
that the evolution of milk has been constrained in order to maximize
the survival of both mother and offspring," said Juan Medrano, a
professor of animal genetics in UC Davis' Department of Animal
In the study, the researchers examined the genomes of cattle, humans,
dogs, mice and rats -- all mammals that carry their young for long
periods in the mother's body, where they are nourished by a placenta.
This genome comparison also included the opossum, as representative
of marsupials, which carry their young in a pouch after birth, and
the platypus, which is one of only two species of mammals that lay
eggs rather than giving birth to live young.
By comparing the genes of these seven species of mammals, they
discovered that, compared to other cattle genes, the individual milk
and milk-production genes are:
* more likely to be found in all mammals, despite the wide
diversity of lactation strategies;
* more likely to be duplicated in placental and marsupial species;
* less likely to have changed as news species evolved; and
* evolving more slowly in cattle than in other species.
The researchers also found that the milk proteins that remained the
same across species were those proteins related to secreting milk in
mammals. Conversely, those milk proteins that had diverged the most
from species to species were those associated with the nutritional
and immunological components of milk.
This suggests that the immunological component of milk is tailored to
the particular needs of each species and highlights the need for
future nutrition research to examine how foods might be tailored to
meet individual immunological needs, the researchers noted.
The research consortium and funding
The Bovine Lactation Genome Consortium is a team of 19 scientists
with specialties spanning molecular biology, immunology, food
science, evolutionary biology, bioinformatics, statistics, mammary
biology, animal genetics and bovine biology. The team was born out of
the International Milk Genomics Consortium, which was initiated in
2004 by UC Davis scientists and housed at the California Dairy
Research Foundation to study the biological processes underlying
mammalian milk genomics. More information about the consortium and
its members is available at: <http://lactoknow.ucdavis.edu/>.
Funding for researchers participating in the bovine lactation genome
study was provided by the International Milk Genomics Consortium, the
National Institute of Environmental Health Sciences, the U.S.
Department of Agriculture Agricultural Research Service, New
Zealand's Foundation for Research Science and Technology, the
California Dairy Research Foundation, the National Human Genome
Research Institute, Genome Canada and Genome BC, the Swiss National
Science Foundation, Australia's Cooperative Research Centre for
Innovative Dairy Products, and the Gardiner Foundation.