First marsupial genome published

Researchers based at the Broad Institute of MIT (Massachusetts Institute of Technology) and Harvard have read the entire genetic code of the South American opossum, Monodelphis domestica. The study, published in the journal Nature, details the first marsupial genome to be sequenced. It reveals that most of the key genetic changes in the evolution of human have taken place in 'control' regions of DNA, rather than genes. The findings will help track the causes of human diseases, say the team - particularly those involved in skin cancer and high cholesterol, both of which can also affect opossum.

The opossum genome is helping to shed light on human evolution, by highlighting key genetic differences between placental mammals, such as humans, mice and dogs; and marsupial mammals like opossums, koalas and kangaroos. The two types of animals last shared a common ancestor around 180 million years ago. 'The opossum genome occupies a unique position on the tree of life', said Francis Collins, director of the National Human Genome Research Institute, adding that the new study 'fills a crucial gap in our understanding of how mammalian genomes, including our own, have evolved over millions of years'.

Interestingly, the scientists found that most recent evolutionary change has occurred in regulatory sections of DNA that fine-tune the activity of nearby genes - rather than mutations that change the actual proteins produced by genes. They also discovered that although the opossum's genetic information is bundled into just nine pairs of chromosome, compared to the 23 pairs of human chromosomes, the total length of its DNA is longer - 3.4 billion base-pairs (DNA 'letters') rather than 3 billion. The team found that the fastest evolving opossum genes were those involved in immunity to diseases, reproduction and adaptation to new diets. According to Leo Goodstadt, of the University of Oxford, 'observing how genes in other species have successfully dealt with parasites and bacteria could suggest new ways to approach development of therapies to battle human infections'.