Canine transmissible venereal tumour (CTVT) was once thought to be an abnormal cell type resulting from cellular mutation. However recent studies on the progress of the disease show that the tumour can evolve into a transmissible parasite. Dogs infected by CTVT follow the pattern of rapid and progressive growth in the initial stage and spontaneous regression of the tumour 3-9 months after infection. Hosts gain immunity for the tumour whereas uninfected dogs gain immunity by infusion of serum from recovered dogs. The tumour is particularly ‘virulent’ in dogs that are elderly, in poor condition or immunosuppressed. It is also histiocytic and transmitted among dog by licking, biting and sniffing affect area with similar condition observed in Tasmanian devil.
The study collected and compared tumour and blood samples from CTVT affected dogs in 5 continents. The DNA sequencing of the tumour confirms the hypothesis that the tumour is contagious as the tumours shows evidence of coming from the same neoplastic cell ancestor 200-2500 years ago in wolf or old Asian dog breeds, diverging into 2 subclades early on in evolution. The DNA sequencing shows that although the tumour is highly aneuploid, its genome is very stable once it had developed into a transmittable parasite with moderate diversity in microsatellite DNA sequences. However, its DNA is highly stable due to the presence of a high active level of telomerase that stabilizes the abnormal karyotype. It appears there is no mutation or recombination mechanism of DNA in the tumour cell and the DNA does not seem to be affected by Muller’s ratchet in the form of genome degradation.
Primary Source:
Murgia, C. Pritchard, J. K. & Su, Y. K. (2006). Clonal Origin and Evolution of a Transmissible Cancer. Cell, 126 477-487.
Secondary Sources:
Tasmaninan devil cancer: http://www.dpiw.tas.gov.au/inter.nsf/WebPages/LBUN-5QF86G?open
CTVT: http://en.wikipedia.org/wiki/Sticker's_sarcoma
Aneuploid: http://cancerweb.ncl.ac.uk/cgi-bin/omd?aneuploid
Telomerase: http://en.wikipedia.org/wiki/Telomerase
Lok Yiu Angela Ho (41793163)
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