POSSUM GENOME A BOOST FOR RESEARCH
The genetic code of a marsupial has been unravelled for the first time, providing important clues fro
human medicine and insights into the great evolutionary split between the two tow major branches of
the mammal family tree.
The completed genome of the grey short-tailed possum promises to help scientists develop ways of
treating paralysis by repairing spinal-cord injuries, as well as shedding light on conditions such as
heart disease and skin cancer.
The grey short-tailed possum, which has the Latin name, Monodelphis domestica, is native to South
America. It was chosen as the first marsupial to have its genome mapped because it is already a
valuable model for studying human disease. Possums have several unusual physiological
characteristics that make them useful in the laboratory. These will become much simpler to study with
knowledge of the genome, which was sequenced from a strain bred in captivity at the Southwestern
Foundation for Biomedical Research in San Antonio, Texas.
Baby possums suffering from a crushed spinal cord can regerate a cord until they are about one week
old, and scientists researching therapies for paralysis are investigating which genes allow this kind of
healing. The DNA sequence will assist the research.
The small marsupials are also the only mammals apart from human beings to develop malignant
melanoma, the most aggressive form of skin cancer, solely as a result of exposure to UV light. As
cancer is caused by damage to DNA, the genome will enhance the possum's usefulness as a
laboratory organism for developing new treatments.
Other areas of medicine that will benefit include cardio-vascular disease, in which possums are used
tho study the effects of high blood cholesterol, and foetal development. Grey short-tailed possums are
born at the equivalent stage of a six-week old human foetus, allowing researchers to study their
growth without invasive procedures.
John VandeBerg, chief scientific officer of the Southwestern Foundation, says: "Trying to find these
genes has been extremely difficult without having the sequence of the animal. But now that the
sequence is available, I expect it to eliminate as much as one to three years of preliminary work before
a researcher can zero in on a gene or set of genes that appears to play a role in a certain disease or
illness."
Details of the genome are published in the prominent scientific journal, Nature, and several papers
analysing it are published in another journal, Genome Research. these have revealed that the species
shares about 69% of its genes with humans. It is also a good species for genetic comparisons with
humans, as both have a similar number of genes - about 18,000 to 20,000 for possums, and about
20,000 to 25,000 for humans. The sequence is also important for evolutionary biology, giving a fresh
look at the divergence of marsupial mammals from the placental mammals about 180 million years
ago.
[Article written by Mark Henderson and published in the Christchurch Press, Discovery section, Friday
11 may 2007, reprinted from an original The Times article]