Thursday, 17 May 2012

The Tasmanian Devil: Light shed on the epidemic contagious cancer.


In a study published early 2012, a group of scientists have successful sequenced the genome of the contagious cancer threating the future survival of the Tasmanian Devil. The current number of non-captive devils is unknown, in the mid-1990s numbers are estimated to be over 100,000 and by 2005 the numbers had dropped by 65% (5). Models suggest numbers lay at around the 40,000 mark (2).
The Tasmanian Devil is the largest carnivore marsupial and has been an endangered species since 2008. Since the first discovery of the contagious cancer known as devil facial tumour disease (DFTD)(1), scientists believed that the Tasmanian devil would have been extinct within 10 years with a 50% decrease in three years (5). DFTD was first noticed in 1996, on a female devil. Now fifteen years on, scientists have final shed information on how the cancer is spread and hypothesis for the future how to prevent these venerable species (1).
After sampling 69 different, non-captive Tasmanian devils tumours scientists have concluded that genetic differences have been discovered. This information has indicated that the tumours have diverged from the original strain over the 15 years the disease has spread throughout the population. This data has also been useful in creating a build up a profile of the cancer’s spread in the population. Another theory for the profile is that some cancer strains or sub-types are more infectious and aggressive than others. DFTD is so contagious that mating, touching of the tumour or biting will transmit this cancer.
The genome of cancers are characterised by  frequent single-base substitution mutations, translocations of segments, insertions and deletion of segments (3, 4).
Genome sequencing found between 15,000 and 17,000 single-base substitution mutations since the contagious tumour diverged from the original strain. The resent strains called 87T and 53T are largly different. 87T is located in southern Tasmania and has 13 chromosomes whereas 53T is located in northern populations with 32 chromosomes (3).

References
1.      Science Daily 2012, Preventing the Tasmanian Devil’s Downfall: Genome of Contagious Cancer Sheds Light On Disease Origin and Spread, viewed 10 March 2012, <http://www.sciencedaily.com/releases/2012/02/120216133442.htm
2.      Price, M 2010, For Conservationists, the (Tasmanian) Devil Is in the Details, viewed 11 March 2012, <http://news.sciencemag.org/sciencenow/2011/06/for-conservationists-the-tasmani.html
3.      Elizabeth P. Murchison, Ole B. Schulz-Trieglaff, Zemin Ning, Ludmil B. Alexandrov, Markus J. Bauer, Beiyuan Fu, Matthew Hims, Zhihao Ding, Sergii Ivakhno, Caitlin Stewart, Bee Ling Ng, Wendy Wong, Bronwen Aken, Simon White, Amber Alsop, Jennifer Becq, Graham R. Bignell, R. Keira Cheetham, William Cheng, Thomas R. Connor, Anthony J. Cox, Zhi-Ping Feng, Yong Gu, Russell J. Grocock, Simon R. Harris, Irina Khrebtukova, Zoya Kingsbury, Mark Kowarsky, Alexandre Kreiss, Shujun Luo, John Marshall, David J. McBride, Lisa Murray, Anne-Maree Pearse, Keiran Raine, Isabelle Rasolonjatovo, Richard Shaw, Philip Tedder, Carolyn Tregidgo, Albert J. Vilella, David C. Wedge, Gregory M. Woods, Niall Gormley, Sean Humphray, Gary Schroth, Geoffrey Smith, Kevin Hall, Stephen M.J. Searle, Nigel P. Carter, Anthony T. Papenfuss, P. Andrew Futreal, Peter J. Campbell, Fengtang Yang, David R. Bentley, Dirk J. Evers, Michael R. Stratton. 2012, Genome Sequencing and Analysis of the Tasmanian Devil and Its Transmissible Cancer. Cell 148, pp780-791 DOI: 10.1016/j.cell.2011.11.065
4.      Mardia, E.R. and Wilson, R.K. 2009, Cancer Genome Sequencing: A Review, Human Molecular Genetics, vol. 18, issue 2, pp163-168. DOI: 10.1093/hmg/ddp396
5.      IUCNRedlist 2012, The IUCN Red List of Threatened Species: Sarcophilus harrisii, viewed 14 March 2012, <http://www.iucnredlist.org/apps/redlist/details/40540/0

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