MOLECULAR CHARACTERIZATION OF MD TUMORS WITH RESPECT TO CLONALITY, LOSS OF HETEROZYGOSITY, AND MDV INTEGRATION

Authors: Cheng, Hans; Hunt, Henry; DELANY, MARY - UNIV OF CALIF - DAVIS

Submitted to: Workshop on Molecular Pathogenesis of Marek's Disease and Avian Immunology
Publication Type: Abstract Only
Publication Acceptance Date: 8/5/2006
Publication Date: 8/5/2006
Citation: Cheng, H.H., Hunt, H.D., Delany, M.E. 2006. Molecular characterization of MD tumors with respect to clonality, loss of heterozygosity, and MDV integration [abstract]. 4th International Workshop on Molecular Pathogenesis of Marek's Disease Virus. p. 6.

Interpretive Summary:

Technical Abstract: With the generation of the chicken genome sequence and new techniques, it is more feasible to elucidate the molecular mechanisms for tumor formation and induction by MDV. In a preliminary study, we analyzed MD tumors using two techniques. T cell receptor (TCR) spectratyping monitors the clonality of tumors by analyzing TCR mRNA. Due to the recombination machinery of the lymphocytes, normal T cells will produce a spectrum of amplicons spaced 3 bp apart (one codon) while clonal samples will be enriched for one or a few products. Our results suggest that MD tumors within a bird are not necessarily clonal, which implies that tumor induction need not be a rare event. The second technique used was SNP typing to test for loss of heterozygosity (LOH), a chromosomal abnormality often found and indicative of certain tumors. In an initial genome-wide genotyping screen, chromosome 28 showed consistent LOH for all informative markers; chromosome Z also showed LOH although since we did not know the sex of the birds, the genotype could be explained if all were females (i.e., ZW with only one Z). In a second SNP screen that quantified allele-frequency by pyrosequencing of chromosome 28 SNPs, 27 of the 33 samples yielded LOH for at least 1 of the 5 informative SNPs. However, the patterns were complex and not all birds were judged to have lost the entire chromosome. In both screens, the same allele was lost for all tumors, which implies that a tumor suppressor gene may be involved. Designed matings are underway to yield MD tumors that will be examined by both TCR spectratyping and LOH on chromosomes 28 and Z. In addition, fluorescence in situ hybridization (FISH) will be employed to confirm LOH, as well as determine if and where the viral genome is integrated. When completed, these studies should provide a much better understanding of MDV pathogenesis and tumor formation as related to host genome alterations