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 23 or more years. First identified in 1996, the spread of this cancer has gotten so pervasive that the animal–the world’s largest carnivorous marsupial–has now become one more 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 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 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. Howver, this “protective” hunting practice ended in 1941 when thy became an officially protected species.

Source - GO Media - Written by Michael Ricciardi - photo credit: Wayne McLean on wikipedia.org