Marsupials diverged from a common ancestor with placental mammals, a group including humans, approximately 180 million years ago. Marsupials and placental mammals are more closely related to one another than to any other vertebrate model species, such as birds, amphibians or fish, yet marsupials are also genetically distinct from all current mammalian biomedical research models. This makes the marsupial an integral part of evolutionary and biomedical studies.
Kangaroos of Australia and the North American opossum, which is abundant in Louisiana, typically come to mind when one thinks of marsupials. However, Monodelphis domestica, a South American opossum, was chosen for genome sequencing because it is the predominant laboratory-bred research marsupial in the world and therefore represents an important model organism for comparative genomics. Studies in this species will help to identify genome features common to all mammals and will also help to pinpoint specific differences between placental and non-placental mammals.
"Mapping the opossum genome is a significant achievement for many reasons," said Mark Batzer, Andrew C. Pereboom Alumni Departmental Professor of Biological Sciences at LSU, and one of the project investigators. "It provides unprecedented insight into connections between humans and other species and will help elucidate the underlying genetic mechanisms that are common in mammals versus the evolution of distinctly human differences in gene regulation, expression and function."
The evolution of mobile elements, or "jumping genes," in mammalian genomes is a primary focus of Batzer's research at LSU. Mobile elements were generally thought to have no function, yet these elements have been shown to cause diseases in humans and also be involved in the creation of new gene families. As a consequence, understanding the impact of mobile elements on genome structure is paramount to understanding the function of the gene.
Batzer and his colleagues, Andrew Gentles, a researcher at Stanford University, David Pollock of the University of Colorado Health Sciences Center and Jerzy Jurka from the Genetic Information Research Institute, investigated the overall mobile element composition and evolution of mobile elements within the opossum genome in the main Nature paper and report additional detailed findings in a companion paper to be published in Genome Research, also on May 10. They found that mobile elements make up about 52 percent of the opossum genome, compared to only about 50 percent in primate genomes, and have distinct compositional differences as well.
In addition, they report that transposable elements appear to have been involved in a specific biological function, perhaps regulating gene expression. Thus, the mobile elements that are typically thought of as "junk DNA" have played a creative role in genome evolution – spreading key genetic innovations involved in the control of gene expression across the genome.
Mobile elements are also commonly utilized for studies of population and species-specific genetic diversity. The genetic diversity and ancestral population structure of recently active mobile elements in diverse opossum populations is the topic of a second companion paper to be published shortly in the journal Gene. These detailed analyses were performed in collaboration with Pollock, Gentles, Jurka and David Ray of West Virginia University.
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For more information on the sequence and analysis of the opossum genome or mobile elements, please contact Mark Batzer at 225-578-7102 or mbatzer@lsu.edu.
*Media Note: Batzer will be out of town until Friday, May 11. He asks that media interested in speaking with him send an e-mail and he will contact them immediately.
More news and information can be found on LSU's home page at www.lsu.edu
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