Submitted to: Avian Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/1/2005
Publication Date: 8/1/2005
Citation: Zhang, H.M., Bacon, L.D., Cheng, H.H., Hunt, H.D. 2005. Development and validation of a PCR-RFLP assay to evaluate TVB haplotypes coding receptors for subgroup B and subgroup E avian leukosis viruses in White Leghorns. Avian Pathology. 34(4):324-331. Interpretive Summary: Avian leukosis viruses (ALVs) are common and naturally occurring viruses that can induce cancer-like diseases and other production problems in chickens. Study of the genetic control of resistance to ALVs began in the 1940's. Since then, several serological tests were developed to directly identify genetic resistance to ALV. The most common test that is currently being used is a virus marker or antigen test, also known as the p27 test. Another test utilizing aggregation of red blood cells, known as R2 antibody test, detects endogenous ALV, an ALV that is genetically inherited by chickens. These serological tests, however, do not reveal exact genetic composition of individual chickens that determines if a chicken is resistant or susceptible to a specific subgroup of ALV. Using previously published chicken gene information, we have developed a DNA-based method that can be used to determine susceptibility or resistance of chickens to ALV. The method is capable of detecting six genetic compositions that control resistance to three subgroups (B, D, and E) of ALVs. This is the first molecular genetics tool that can simultaneously determine all six genetic compositions of susceptibility or resistance to these three subgroups of ALV. Furthermore, our experimental data showed that this molecular method is more accurate than the previously existing methods used to determine resistance and susceptibility to ALV. This new genetic method should be valuable to geneticists in academia and industry who are interested in developing chicken lines that are resistant to ALV.
Technical Abstract: The cellular receptor of subgroup B avian leukosis virus (ALVB) is encoded by a gene at the tumor virus B (TVB) locus. TVB alleles encode specific receptors permitting infection by exogenous ALVB or ALV subgroup D (ALVD) as well as endogenous ALV subgroup E (ALVE). Two single nucleotide polymorphisms (SNP) at the TVB locus have been reported distinguishing three TVB alleles (TVB*S1, TVB*S3 and TVB*R). We have developed a PCR-RFLP assay using the two SNPs to define different allelic haplotypes that constitute six possible TVB genotypes. Chickens from parents heterozygous for different TVB alleles were challenged with Rous sarcoma viruses of subgroup ALVB and ALVE to induce wing-web tumors. Tumor incidences were evaluated between chickens of the genotypes determined with this newly developed PCR-RFLP assay. Importantly, chickens typed with this assay as TVB*S3/*S3 were resistant to infection by subgroup ALVE, and those TVB*R/*R were resistant to both ALVE and ALVB. Furthermore, a vast majority of chickens with the susceptible TVB*S1/- genotypes developed a tumor. This PCR-RFLP assay enables a relatively rapid assessment of all six anticipated TVB genotypes in chickens produced by TVB* heterozygous matings and this noninfectious assay should be useful for selection and breeding of chickens with genetic resistance to infections by ALVB, ALVD and ALVE.