Friday, 13 April 2012

Devil Facial Tumour Disease Genome Mapping
Sophie Hudson

Devil facial tumour disease, or DFTD, is a form of cancer that is currently a huge threat to the wild Tasmanian devil population. It generally kills Tasmanian devils about three months after they contract it, and causes huge tumours on their mouth and throat. This can obstruct their breathing and render them unable to eat. DFTD is strange because, unlike most other forms of cancer, it is contagious. The devils bite each other on the face, their immune systems don’t pick up the pathogens, and the disease is spread. Mutations within the genome of the cancer cell have promoted its spread and it is a popular belief that low genetic diversity, due to population isolation, makes the cancer easier to pass on. Despite this there is no real certainty regarding why it isn’t picked up by the animal’s defensive immune system.
Murchison et al, 2012 1

DFTD is believed to have arisen in northeast Tasmania in 1996. The disease began within the cells of a single female devil, and has since evolved into a contagious clonal variation. The specific ways with which this clonal version mutated and works are not known.
There is a lot of research that is being conducted to try to put an end to DFTD. Studies conducted in February managed to map the genome of the cancer.  There are two forms of the disease; the form that causes facial tumours and a form that has been transferred into organs. The study compared these two forms, to each other and to a healthy devil, using the cell linings of an effected lung, a tumour, and the genome map of a devil without DFTD.

The comparison found that the genome of the tumour cells had 691 328 single base substitutions and the lung cells had 699 156. On top of this, the tumour cells had 37 240 insertion and deletion DNA mutations, and the lung cells had 307 631. It is clear that there are mutations that turn healthy genes into diseased ones. On top of this, the study suggested that there are mutations, or somatic variations, that have arisen since the cancer became aggressive and contagious.

To further investigate this theory, the genome of the first known Tasmanian devil to have had the cancer was mapped. It was found that there were changes in the base mutations between this genome and the originally mapped DFTD genomes. The parents of the devils that the diseased cells in the original test came from also had their genome mapped, and there was no difference in the genomes. This result shows that the two different types of cancer are from the same, original DFTD strain, which has since mutated into the two different strains.
This research is important for assuring the future of the devils. Understanding the progressions and the genetic changes of the genome will help in finding a cure and a solution to ridding Tasmania of the disease. Hopefully, the cancer that threatens the species with extinction will be wiped out.

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