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Researchers produce most detailed map of cattle genome

Jim Barlow, Life Sciences Editor
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CHAMPAIGN, Ill. -- The most detailed map ever produced of cattle genes and the first comparison map of cattle and human genomes show that many genes, and even whole chromosomes, are configured in the same way in the two species, scientists report.

"The comparative map has enormous predictive power," said lead researcher Harris Lewin, director of the W.M. Keck Center for Comparative and Functional Genomics at the University of Illinois.

"For the first time, we can move from a point on the human genome to the equivalent point on the cattle genome. That will allow us to use the map of one species to identify genes controlling important traits in the other, such as those influencing lactation, reproduction and resistance to infectious diseases."

The maps appear in the September issue of the journal Genome Research by scientists at two universities after a three-year collaboration led by Lewin, a professor of animal sciences, holder of the Gutgsell Endowed Chair and director of the UI Biotechnology Center.

Among the major contributors to the research were co-authors Mark R. Band, a postdoctoral research associate; Joshua H. Larson, a graduate student in the UI department of animal sciences; and James E. Womack, the W.P. Luse Endowed Professor at Texas A&M University.

A pullout poster of the comparative map is included in the journal, courtesy of AniGenics Inc., an animal genomics company, and Research Genetics, a major supplier of tools and reagents for genome research and subsidiary of Invitrogen Corp.

The research -- funded by the USDA National Research Initiative --combined the sequencing of small segments of genes, known as expressed sequence tags, and sophisticated bioinformatics tools developed at the UI with a radiation hybrid cell panel, a unique resource for gene mapping developed by Womack's laboratory.

A total of 1,087 genetic markers were placed on the radiation hybrid map, which includes 768 known genes. About 92 percent of all cattle chromosomal DNA is included on the map. This represents a four-fold increase in the total number of all cattle genes mapped previously, Lewin said.

Among the known genes, 638 (83 percent) could be identified as identical to human genes that also have positional information on human chromosomes, the researchers reported. Knowing the order of the same genes on the chromosomes of humans and cattle permitted the construction of the first "whole-genome comparative map" and revealed large regions of conservation of gene order in the two genomes.

An examination of the comparative map revealed up to 149 conserved chromosome segments in humans and cattle, including four whole chromosomes that appear to have the same genes in both species, despite the two species being separated by more than 60 million years of evolution.

Among other firsts in the report were the identification of up to 48 novel genes, predicted mapping of 48 unmapped human genes on the basis of the cattle-map position, and the number of chromosome rearrangements during evolution resulting in the present organization of the cattle and human genomes.

Eventually, Lewin said, the cattle genome will be completely sequenced, ultimately leading to a more detailed picture of the evolutionary events that distinguish the different mammals.

"In the end" he said, "we will understand the molecular genetic basis for the major phenotypic differences among the mammals. This will have enormous scientific and practical significance, particularly in the area of food safety, animal health, and the competitiveness of our domestic beef and dairy industries."