Review: Genome and Ingeneering
Tasmanian devils could be extinct in 20 years because of a highly contagious facial cancer called devil facial tumor disease (DFTD). In two papers, researchers have sequenced the genome of the cancer and mapped the chromosome and gene rearrangements, and this could give the animals hope at last. Tasmanian devils are world's largest carnivorous marsupial and are found in only in Tasmania, Australia, and are perhaps best known as a as Taz, the a Looney Tunescartoon character, but the cancer, which has developed from nerve cells, now affects 70% of the population and kills the animals within months, sometimes simply through starvation. In papers published in Cell and PLOS, researchers have sequenced the genome of the contagious cancer, which is passed on through bites.
By sequencing the tumours of different devils across Tasmania and comparing the 20,000 mutations , the paper in Cell found that the cells of all the cancers come from a single female Tasmanian devil known as the 'Immortal Devil', and that some cancers are more virulent than others. The paper in PLOS showed that thechromosomes in the cancer have been rearranged, and that the cancer has actuallyevolved very little since its discovery in 1996.
The spread of cancer between individuals is normally prevented by the immune system, which can normally detect foreign tissues as "non-self". The Tasmania devil cancer sequence includes mutations in a set of genes involved in immunity, which could explain how it outwits the immune system.
"The Tasmanian devil cancer is the only cancer that is threatening an entire species with extinction," says Dr Elizabeth Murchison, lead author of the Cell paper, from the Wellcome Trust Sanger Institute. "Sequencing the genome of this cancer has allowed us to catalogue the mutations that caused this cancer to arise and to persist in the Tasmanian devil population."
The next step is to map the genomes of thousands of devil tumours in order to understand the genetic diversity present in the cancer and to investigate the genetic interactions between the cancer and the Tasmanian devil population. Knowing more about the cancer could help work out how to prevent or treat the disease in Tasmanian devils, or could be useful in the unlikely event that such a cancer could arise in humans. The Tasmanian devil genome was first sequenced in June 2011.
The genetic changes occurring in endangered species might increase their extinction probabilities. Low population sizes leads to reduced genetic diversity and increased inbreeding. A low of genetic diversity means a reduced ability to adapt to environmental changes. Inbreeding is often associated to reduced reproduction and survival. Genetic factors might thus play an important role in species extinction -and therefore in their conservation.
Molecular genetic markers are often used to assess the genetic status of endangered species and populations. This information is then used to elaborate conservation plans designed to maximize genetic diversity and minimize inbreeding.