Submitted to: Cytogenetics and Genome Research
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/21/2006
Publication Date: 7/31/2007
Citation: Cheng, H.H., Zhang, Y., Muir, W. 2007. Evidence for widespread epistatic interactions influencing Marek's disease virus viremia levels in chicken. Cytogenetics and Genome Research. 117:313-318. Interpretive Summary: Marek’s disease (MD) is an economically-important disease of chickens caused by a pathogenic virus known as the Marek’s disease virus (MDV). Currently, vaccines have controlled the problem but new emerging viral strains that vaccines cannot control are being encountered more frequently. With the advent of the chicken genome sequence and other modern genomic tools, the possibility exists to identify genes that confer resistance to MD. This information could be used in breeding programs to select for chickens with superior disease resistance. In this paper, we show that many more important regions containing disease resistance genes can be found if you incorporate 2-way epistatic interactions into the analyses. This result suggests that MD resistance is highly complex and involves interacting networks. This information greatly enhances our understanding of this MD resistance and has implications on other complex traits and the ability to improve animals through genetic markers.
Technical Abstract: Marek’s disease, a T cell lymphoma induced by the Marek’s disease virus (MDV), is the main chronic infectious disease concern threatening the poultry industry. Enhancing genetic resistance to MD in commercial poultry is an attractive method to augment MD vaccines, which is currently the control method of choice. In order to implement this control strategy through marker-assisted selection (MAS), it is necessary to identify quantitative trait loci (QTL) or genes that influence MD incidence. Previous studies have demonstrated that it is possible to identify QTL that confer MD resistance in both experimental and commercial chickens. With the advent of the chicken genome sequence and new genomic tools, the line 6 x 7 F2 experimental resource population was re-evaluated by screening 3072 single nucleotide polymorphism (SNP) on 80 selective progeny and testing for the presence of 2-way epistatic interactions. As a result of having 709 fully informative genetic markers, a large number of highly significant interactions that involved loci located through the majority of the genome were identified that account for Marek’s disease virus (MDV) viremia titers in infected birds. Even after five rounds of screening where the most significant locus was removed, many highly significant interactions remained. These results suggest that resistance to MD is highly complex and will require the incorporation of epistatic interaction analyses and functional genomic approaches to reveal the underlying genetic basis.