The Origin of the Tasmanian Devil Clonally Transmissible Cancer

by Elena Shanti Franchina

 

The transmissible cancer known as devil facial tumor disease (DFTD) has endangered the devil population in Tasmania, causing its number to collapse since 1996, date when it was first observed in northeastern Tasmania.

An international team of scientists led by Elizabeth Murchison, an investigator at Cold Spring Harbor Laboratory (CSHL), have discovered that the deadly facial tumors decimating Australia’s Tasmanian devil (Sarcophilus harrisii) probably originated in Schwann cells, a type of tissue that insulates and protects nerve fibers. The discovery comes from the effort of the team to carry out a genetic analysis of tumor cells. Based on these data, scientists have identified a genetic marker to accurately diagnose the DFTD.

The DFTD is a unique type of cancer: it is derived from neuroectoderm and is composed of undifferentiated round to spindle-shaped cells with few defining ultrastructural features. The genotype of all DFTD-tumors is similar across all loci, regardless of location, sex or age of the devil. One of the features that make this tumor nothing like previously described devil cancers is the fact that cancer cells are transmitted horizontally from animal to animal through biting. Biting is a normal part of the devil’s behaviour, involved in simple play and reproduction, this is the reason why the disease is highly spread among the population. This mechanism resemble that involved in canine transmissible venereal tumor (CTVT) and a transmissible sarcoma affecting Syrian hamsters, still this type of cancer remain unique in some of its features.

The tumor affects the face and mouth primarily, and lead to death by starvation or due to metastasis to internal organ. So far, no diagnostic tests or vaccines are present for DFTD, and models predict the disappearance of the Tasmanian devils within 25-35 years, due to this disease. “Our discovery is a major step forward in the race to save the Tasmanian devil from extinction,” notes Dr. Murchison, who points out that this research has provided a method to distinguish the DFTD from other cancers that affect the marsupial, allowing easy identification and isolation of affected animals.

The analysis presented in this study, propose that DFTD likely originated in the Schwann cells of a single devil. Schwann cells are found in the peripheral nervous system and produce myelin and other proteins essential for the functions of nerve cells in the tissue.  25 tumors were sampled in the process and they were all found to be genetically identical. Using miRNA deep sequencing and transcriptomes, a match was found for Schwann cells, revealing high activity in many of the genes coding for myelin basic protein production. Moreover several marker were identified, that may enable a more accurate discrimination of DFTD from other types of cancer and may eventually help identify a genetic pathway that can be targeted to treat it.

The researches also compiled a catalog of genes that may influence the pathology and transmission of the tumor, and can help develop a DFTD preclinical test and vaccine. Also further compared analysis of the DFTD and the canine clonally transmissible cancer, could lead to deeper insights in their occurrence, evolution and biology, potentially helping saving the devil from extinction.

 

 

Journal Reference: Science, DOI: 10.1126/science.1180616.

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