Single nucleotide polymorphism variants within tva and tvb receptor genes in Chinese chickens

Abstract

Avian leukosis is an immunosuppressive neoplastic disease caused by avian leukosis viruses (ALV), which causes tremendous economic losses in the worldwide poultry industry. The susceptibility or resistance of chicken cells to subgroup A ALV and subgroup B, D, and E ALV are determined by the receptor genes tumor virus locus A (tva) and tumor virus locus B (tvb), respectively. Four genetic resistant loci (tva(r1), tva(r2), tva(r3), and tva(r4)) in tva receptor gene and a genetic resistant locus tvb(r) in the tvb receptor gene have been identified in inbred lines of White Leghorn. To evaluate the genetic resistance to subgroup A, B, D, and E ALV, genetic variations within resistant loci in tva and tvb genes were screened in Chinese local chicken breeds and commercial broiler lines. Here, the heterozygote tva(s1/r1) and the resistant genotype tva(r2/r2), tva(r3/r3), and tva(r4/r4) were detected in Chinese chickens by direct sequencing. The heterozygote tva(s1/r1) was detected in Huiyang Bearded chicken (HYBC), Rizhaoma chicken, and commercial broiler line 13 to 15 (CB13 to CB15), with the frequencies at 0.08, 0.18, 0.17, 0.25, and 0.15, respectively. The resistant genotype tva(r2/r2) was detected in Jiningbairi chicken (JNBRC), HYBC, and CB15, with the frequencies at 0.03, 0.08, and 0.06, respectively, whereas tva(r3/r3) and tva(r4/r4) were detected in 19 and 17 of the 25 Chinese chickens tested, with the average frequencies at 0.13 and 0.20, respectively. Furthermore, the resistant genotype tvb(r/r) was detected in JNBRC, CB07, CB12, CB14, and CB15 by pyrosequencing assay, with the frequencies at 0.03, 0.03, 0.11, 0.09, and 0.15, respectively. These results demonstrated that the potential for genetic improvement of resistance to subgroup A, B, D, and E ALV were great both in Chinese local chickens and commercial broilers. This study provides valuable insight into the selective breeding for chickens genetically resistant to ALV.

Türkiye Yerli Tavuk Irklarında Tümör Viral B Lokusunun Belirlenmesi

“…Taken together, these studies show that the TVB*S1 allele is the common allele and that the TVB*R resistance allele is seldom observed in native chickens. Consistent with the results of analyses in Chinese [6,12,13] and Indian [11] domestic chicken breeds, the TVB*R allele was rarely observed in Turkish native breeds. These results are parallel to the observation that the TVB*R allele frequency in native chicken breeds is lower than that observed in WL populations [6] .…”

“…Another study, conducted with a total of 1428 chickens from ten domestic Chinese breeds and 15 commercial broiler flocks, the frequencies of TVB*S1, TVB*S3, and TVB*R alleles varied between 0.71 and 0.91, 0.00 and 0.09, and 0.04 and 0.29, respectively. Eleven of the 25 breeds were homozygous for the TVB*S1 allele and five breeds of those had the TVB*R/R resistant genotype at varying frequencies (ranging from 0.03 to 0.15) [13] .…”

“…While there are no vaccines for ALV diseases, genetic resistance is very important to protect chickens [14] . Additionally, Liao et al [13] noted that the TVB*R allele could be used to improve laying performance and reduce lymphoid leukosis in chickens. Therefore, selection of chickens with TVB*R alleles could improve lifespan as well as egg and meat production in native breeds.…”

Naturally Occurring Frameshift Mutations in the tvb Receptor Gene Are Responsible for Decreased Susceptibility of Chicken to Infection with Avian Leukosis Virus Subgroups B, D, and E

“…In our previous study, we identified intronic deletions of the tva receptor gene that result in reduced susceptibility to subgroup A ALVs (18). This finding is suggestive for the presence of similar genetic mutations within other ALV receptor genes, and Chinese broiler lines that have undergone long-term virus eradication measures may manifest such recessive alleles (30). Two tvb allelic variants were identified in Chinese commercial broiler lines by generating a series of amplicons for the genomic region of the tvb receptor gene followed by sequencing, which were designated the tvb r4 and tvb r5 alleles.…”

“…Thus, populations of chickens exposed to ALVs may be subjected to selection pressure, which mediates development of host complete or partial genetic resistance to ALV infection. In order to identify additional resistance alleles of ALV receptor loci, we systematically screened specific receptor genes in a panel of Chinese commercial broiler lines for naturally preexisting polymorphisms (30). We have previously identified two tva alleles causing reduced susceptibility to ALV-A infection that resulted from intronic deletions within the tva receptor gene (18).…”