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Marsupial genome reveals insights into mammalian evolution
January 31, 2006The genetic code of marsupials has now been documented for the first time. An international team led by Kathy Belov from the University of Sydney's Faculty of Veterinary Science published an analysis of the marsupial genome in the open access journal PLoS Biology. The paper details the evolution of an important cluster of immune genes known as the MHC using available genome sequences of the gray, short-tailed opossum (Monodelphis domestica), a marsupial found in South America.
"Mapping the opossum MHC has allowed us to deduce what the MHC of ancestral mammals looked like," says Belov. "We think it contained several different types of immune genes in a single complex. These genes are no longer found in a single complex in any living animal but are scattered over various chromosomes. We have named this complex 'The Immune Supercomplex.'"
Belov et al. found that while the size and complexity of the opossum MHC is closer to eutherian (placental) mammals, its organization is closer to fish and birds. "The clues we unearthed by looking at different genomes are also helping us to understand how our own intricate immune system evolved from the relatively simple immune system seen in lower vertebrates such as birds and fish," says Belov.
"Interest in marsupial and monotreme genomes comes from their important positions in vertebrate evolution," says Belov. (Monotremes are egg-laying mammals, represented today by only the platypus and echidna.) "Comparing genes of placental mammals, such as the human and the mouse, is not very efficient because their genes can be so similar it is hard to pinpoint regions that remain unchanged because they serve a particular purpose. In contrast, comparison of distantly related genes, such as the chicken and human, can be difficult, because the sequences are so different."
"Marsupial and monotreme genomes fill this gap. They are easily aligned with placental mammal genomes, yet are different enough to pinpoint regions that have important functions and therefore have been conserved for long periods of time. The monotremes split off from other mammals 210 million years ago. The remaining marsupials split from the main (placental) group about 180 years ago."
Significantly, the authors also found data supporting the idea that there was an ancient relationship between the MHC and another critical component of the immune system, the natural killer complex (NKC), which contains natural killer (NK) cell receptor loci. This "immune supercomplex," which no longer exists in modern genomes, performed the MHC functions in ancestral mammals. "Understanding the immune system of marsupials and monotremes will help us to conserve our native species," Belov says.
Public Library of Science
"Interest in marsupial and monotreme genomes comes from their important positions in vertebrate evolution," says Belov. (Monotremes are egg-laying mammals, represented today by only the platypus and echidna.) "Comparing genes of placental mammals, such as the human and the mouse, is not very efficient because their genes can be so similar it is hard to pinpoint regions that remain unchanged because they serve a particular purpose. In contrast, comparison of distantly related genes, such as the chicken and human, can be difficult, because the sequences are so different."
"Marsupial and monotreme genomes fill this gap. They are easily aligned with placental mammal genomes, yet are different enough to pinpoint regions that have important functions and therefore have been conserved for long periods of time. The monotremes split off from other mammals 210 million years ago. The remaining marsupials split from the main (placental) group about 180 years ago."
Significantly, the authors also found data supporting the idea that there was an ancient relationship between the MHC and another critical component of the immune system, the natural killer complex (NKC), which contains natural killer (NK) cell receptor loci. This "immune supercomplex," which no longer exists in modern genomes, performed the MHC functions in ancestral mammals. "Understanding the immune system of marsupials and monotremes will help us to conserve our native species," Belov says.
Public Library of Science
Marsupial Current Events and Marsupial News RSSWildlife faces cancer threat
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Wildlife Conservation Society supports world's first study of egg-laying mammal
A Wildlife Conservation Society research intern working in the wilds of Papua New Guinea has successfully completed what many other field biologists considered "mission impossible"-the first study of a rare egg-laying mammal called the long-beaked echidna.
New evidence implicates humans in prehistoric animal extinctions
Research led by UK and Australian scientists sheds new light on the role that our ancestors played in the extinction of Australia's prehistoric animals. The study, published this week in the journal Proceedings of the National Academy of Sciences of the USA, provides the first evidence that Tasmania's giant kangaroos and marsupial 'rhinos' and 'leopards' were still roaming the island when humans first arrived.
Living fossil still calls Australia home
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Marsupial lion tops African lion in fight to death
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Parasites might spur evolution of strange amphibian breeding habits
Parasites can decimate amphibian populations, but one University of Georgia researcher believes they might also play a role in spurring the evolution of new and sometimes bizarre breeding strategies.
Burrowing mammals dig for a living, but how do they do that?
Next time you see a mole digging in tree-root-filled soil in search of supper, take a moment to ponder the mammal's humerus bones.
Evolution of genomic imprinting
How we come to express the genes of one parent over the other is now better understood through studying the platypus and marsupial wallaby - and it doesn't seem to have originated in association with sex chromosomes.
LSU professor involved in genome sequencing of the first marsupial
Since the launch of the Human Genome Project, which released a first draft of the entire sequence of human DNA in 2001, many researchers have dedicated themselves to creating a library of comprehensive, species-specific genetic sequence "maps" available for study.
Researchers publish first marsupial genome sequence
An international team, led by researchers at the Broad Institute of MIT and Harvard, and supported by the National Institutes of Health (NIH), today announced the publication of the first genome of a marsupial, belonging to a South American species of opossum.
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