Male Tasmanian Devil
A relatively rare form of transmissible cancer–known as Devil Facial Tumor Disease (DFTD)–has been decimating Tasmanian Devil (Sarcophilus harisii) populations in Northeast Tasmania over the past thirteen or more years. First identified in 1996, the cancer has become so pervasive that the animal–the world’s largest carnivorous marsupial–has now become one of the world’s most endangered species.
Recently, researchers have performed large scale genetic analysis of DFTD tumor cells and have discovered many clues to the cause and nature of the cancer. After sequencing tumor cell genes and analyzing small pieces of non-coding, genetic material known as microRNAs (miRNA), the team has determined that the cancer is a “single clonal cell line propagated as a tumor allograft” and is transmitted from devil to devil through biting. An “allograft” is a transplantation of cells (or tissue) from one (non-genetically identical) member of species to another. Devils are generally solitary hunter-scavengers but are known to occasionally associate in small groups.
The investigating team (Murchison et al) also show evidence that the disease is of Schwann cell origin (or a Schwann cell precursor). Schwann cells are progenitor cells that participate in neural repair and also control immune system responses to local nerve cell growth. Such cells are highly “plastic” (morphologically variable) and their role in immune responses “may be significant in the evolution of DFTD as a transmissible cancer.”
The most highly expressed gene in the analyzed tumor cells–called MBP–encodes basic myelin protein. Myelin is the lipo-protein membrane that sheaths and insulates nerve cells. Based upon this high rate of expression, the researchers concluded that DTFD is a tumor of the myelin sheath. Further evidence for an over-expression of another myelin protein (specific to Schwann cells) called periaxin (PRX) is quite strong, as all of the DFTD tumors tested positive for PRX, while none of the non-DFTD tumors (used as controls) did so, nor did tumor-free tissue.
Reporting in the January 1 2010 edition of Science (The Tasmanian Devil Transcription Reveals Schwann Cell Origins of a Clonally Transmissible Cancer), the authors suggest other Schwann cell genes (such as the NF1 gene ) as good candidates for future DFTD analysis. They also compare DFTD to a similar transmissible cancer found in dogs, known as canine clonally transmissible cancer (CCTC). They recommend future study of these and other transmissible animal cancers to determine their histogenesis (i.e., their formation from undifferentiated cells) and to shed greater light on their evolution and biological roles. Their genetic analysis provides a working “gene catalog” to aid this research.
Tasmanian Devils were eradicated from the Australian mainland, it is believed, nearly three thousand years ago. But they persisted in large numbers on the island of Tasmania. There, they were frequently hunted as they were seen as threats to livestock. However, this “protective” hunting practice ended in 1941 when they became an officially protected species.
photo credit: Wayne McLean on wikipedia.org
About Michael Ricciardi
If they are solitary animals, rather than transmission through biting, perhaps they may transmit through serial consumption of a common scavanged food, i.e. gnawing on the same dead animal, over time, and passing the infection through the gums.
Why not start a colony of healthy TDs on the Ozzy mainland ?
@Gerard: I just had the same thought. Large carnivorous marsupials (namely the Thylacine) persisted on Australia up to historic times, so it wouldn’t be like introducing an exotic species. Their niche would hopefully still be waiting for them (unless the dingos have filled it and outcompete them.) Maybe they could even help out with Australia’s persistent rabbit problem!
napamat:
I had a similar thought when I was writing the piece–that is, that the infection came via bacteria from all that carrion. But then, two thoughts followed: carrion attracts plenty of scavengers and the odds are, a good size piece of carrion will attract more than one devil, thus making it entirely plausible that two devils would get into a fight over same. Secondly, the researchers found no evidence of a bacterial source (though that doesn’t rule out a bacterium), in their sequencing and amplification of the cells; they were able to make perfect clones (bacteria-generated cancers would presumably leave genetic traces; tell-tale SNPs, etc.
Devils are known to be highly aggressive around their food and do bite at each others face. They do this in captivity too (unfortunately often spurred on by the people feeding them in order to put on a show).
People struggle to look after the remaining species we have left here on the mainland, I’d hate to think how tassie devils would fare in such an urban environment. They are already killed by the hundreds on roads in Tasmaina, and Tassie is very much “more wild” than most mainland parts. The ecological balance here is now so out of whack, just re-introducing devils would be nothing other than cruel for them.
They are doing the right thing by keeping them in Tassie and breeding them in captivity, disease free.