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International Team Characterizes Tasmanian Devil Facial Tumors

NEW YORK (GenomeWeb News) – The Tasmanian devil facial tumor disease may have originated from peripheral nervous system protecting cells called Schwann cells, according to a study appearing in the most recent issue of Science.

An Australian and American research team characterized the devil facial tumor disease, or DFTD, using microsatellite genotyping, mitochondrial sequencing, transcriptome sequencing, and microRNA analyses. Their findings suggest the transmissible cancer arose from a single cell line resembling Schwann cells. The researchers have already identified a genetic marker that they believe will be useful for earlier diagnosis of the disease — and say the current study may also aid in coming up with a vaccine or treatment for the disease.

"Our findings represent a big step forward in the race to save the devils from extinction," lead author Elizabeth Murchison, who did the research as a post-doctoral researcher in Gregory Hannon's lab at Cold Spring Harbor Laboratory and in the lab of Australian National University researcher Jennifer Graves, said in a statement.

DFTD, first detected in the mid-1990s, threatens to wipe out wild Tasmanian devil populations within the next 25 to 35 years. The disease is characterized by large tumors on the face and mouth that lead to starvation and can metastasize to other parts of the body. It spreads when an infected Tasmanian devil bites an uninfected animal.

The mysterious and devastating nature of the disease has researchers from several labs scrambling to understand the DFTD biology — and animals' susceptibility to it. For the current study, Murchison and her co-workers first genotyped 25 matched tumor-host samples and ten unaffected Tasmanian devil samples at 14 microsatellite loci.

Consistent with a previous finding suggesting the DFTD sprung from a lone clonal cell line, the researchers found that tumors had the same genotype from one Tasmanian devil to the next, independent of the host's age, sex, or location. This genotype did not match other host tissues or samples from uninfected animals.

When they sequenced 1,180 bases of mitochondrial locus control region sequence in 14 tumor-host pairs and nine unaffected animals, the team found that all of the samples belonged to the same locus control region haplotype, although some animals — including uninfected animals from western Tasmania — shared a SNP within this region.

Meanwhile, cloning and deep sequencing of 10 normal tissues and five tumor tissues turned up 114 Tasmanian devil miRNAs. Again, tumor samples resembled one another but had distinct profiles compared with the tissue-specific miRNA patterns detected in other tissues.

Among the miRNAs that were more highly expressed in DFTD were some previously shown to be up-regulated in other tumors. Known tumor suppressor miRNAs, on the other hand, were found at low levels in DFTD samples.

And the gene expression patterns offered clues about the possible origin of DFTD. The team did transcriptome sequencing of tumor samples and normal Tasmanian devil testis tissue, identifying 31 transcripts that are significantly enriched in tumors compared with testis tissue and 20 transcripts showing at least twice as much expression in tumor tissue.

Overall, the researchers found that gene expression in the tumors most closely resembled that found in Schwann cells. In particular, tumor tissue showed dramatic increases in the expression of MBP, a gene coding for myelin basic protein, as well as several other genes in the pathway producing the nerve insulating material myelin. Schwann cells produce the myelin found in the peripheral nervous system while oligodendrocytes make myelin in the central system.

Among the genes that are specifically expressed in the DFTD cells was PRX, a gene coding for the myelin maintenance protein periaxin. The team's subsequent experiments suggest PRX may serve as a useful genetic marker for distinguishing DFTD tumors from other types of tumors and for finding healthy Tasmanian devils for breeding programs aimed at saving the animals from extinction.

Those involved say additional research is also needed to understand just how the cancer originated.

"Now that we've taken a good look at the tumors' genetic profile, we can start hunting for genes and pathways involved in tumor formation," Hannon said in a statement.

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