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An international team of scientists, including UConn genomicist Rachel O'Neill, sequenced the first complete genome of the koala, reported today in Nature Genetics . The koala genes have already revealed some of the secrets of the furbearing tree, the way it digests toxic eucalyptus leaves and why it is sensitive to chlamydia.
Koalas are marsupials, kangaroos, Tasmanian devils and opossums. Marsupials give birth when their young are still very small and underdeveloped, and then raise babies in a pocket for several more months. They diverged from other mammals a very long time ago, and scientists have suspected that the marsupial genome could answer many questions about mammalian evolution.
"Koalas are an iconic marsupial mammal," says O'Neill. "Everyone knows what a koala looks like, making it a great species to use as an educational tool.But they are in danger because of population collisions in the distant past and an infectious virus emerging."
Understanding their genome – spelling out all the genes and what chromosome, or DNA molecule, each gene is – gives biologists the opportunity it identifies genes related to the koala's response to viruses and identifies the boundaries of population diversity that can guide conservation efforts. O'Neill, director of the UConn Systems Genomics Institute, specializes in marsupials and was involved in the first ever sequenced marsupial genome – the tammar wallaby
The Koala Genome published today is the most complete marsupial genome ever sequenced. the same with the human genome. The consortium of scientists – 54 researchers from 29 different institutions in seven countries – sequenced more than 26,000 genes in the koala genome, making it slightly larger than the human gene. And in a way, says O'Neill, the genome of the koala is actually better than that of humans: the genome of the koala has been defined by its centromeres. Think of the centromere as the place where the two halves of each chromosome are attached; if you imagine the "X" chromosome, the centromere is at the cross of the X. It's a special part of the genome that helps the DNA itself to copy itself.
"This is the first complete genome assembly in an animal containing centromers that have been functionally defined," says O. Neill. Compared to humans, centromere koalas are small, disordered and filled with "jumping genes", fragments of DNA that can move in the genome.
Several unusual models of the koala genome have already answered questions about the koala. For example, koalas live in eucalyptus forests in Australia and subsist almost entirely on eucalyptus leaves, which contain toxic compounds that make other mammals sick when they are eaten in large quantities. Researchers at the Earlham Institute in the UK have noted that the koala genome has a greater number and diversity of genes known to encode metabolic enzymes in the liver that help break down toxins such as those found in eucalyptus leaves
. composition of koala milk. Because koala babies (called joeys) are born at an early stage of development – only 5 weeks of gestation, compared to 9 weeks for dogs or 40 weeks for humans – they need very different types and amounts of milk "Thanks to the high-quality genome, the team was able to analyze and discover koala-specific milk proteins that are essential for the different stages of development," says Katherine Belov of the University of Sydney, the University of Sydney. one of the authors on the study. It also appears that these proteins may have an antimicrobial role, showing activity against a range of bacterial and fungal species, including Chlamydia pecorum strain known to cause blindness and infertility among koalas.
Chlamydia severely reduced koala populations in New South Wales and Queensland. The researchers hope to develop a vaccine using information from the koala genome.
"The genome provides a holistic and scientifically based approach to koala conservation," says Rebecca Johnson, director of the Australian Museum Research Institute and other lead author. 19659003] Wild koalas are currently found in the forest and eucalyptus forests across eastern Australia (Victoria, New South Wales and Queensland), and have been relocated to other sites , like southeastern South Australia. and a very specific diet of eucalyptus leaves has made that koalas are particularly vulnerable to habitat loss due to the clearing of native vegetation for agriculture and urban development. The Australian Federal Government regards Queensland, New South Wales and Australian Capital Territory koala populations as "vulnerable" under national environmental legislation. The research team hopes that koala genome discoveries will help the conservation and protection efforts of the species.
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