Molecular identification of avian leukosis virus subgroup E loci and tumor virus B locus in Chinese indigenous chickens

Avian leukosis virus (ALV) subgroup E (ALVE) is an endogenous retrovirus in the chicken genome. The chickens carrying ALVE locus 3 (ALVE3), 6 (ALVE6), 9 (ALVE9), and 21 (ALVE21) have been proved to be susceptible to ALV. Tumor virus locus B (TVB) encodes the cellular receptor for ALV subgroups B, D, and E. The insertions of the 4 ALVE loci and the genotypes of TVB have not been demonstrated in Chinese indigenous chicken breeds. In the present study, the existence of ALVE3, ALVE6, ALVE9, and ALVE21 were detected in 10 native breeds of Chinese chickens and an introduced breed, the White Leghorn (2 populations in this study, WL1 and WL2), by locus-specific PCR. The PCR products of ALVE were further confirmed by sequencing assay. We also surveyed the status of genotypes of TVB in Si Me, Beijing You, and White Leghorn (WL1 and WL2) chickens with pyrosequencing assays. The results showed that the carrier frequency of ALVE3 was 1.3% in the Chinese chicken population, and was 10.3 in WL1 and 49.2% in WL2. The carrier frequency of ALVE6 was 5.4% in native breeds of Chinese birds, in contrast with 0% in WL1 and 6.8% in WL2. The carrier frequency of ALVE.9 was 0.1% in the Chinese indigenous population, and was 16.0% in WL1 and 11.9% in WL2. The carrier frequency of ALVE21 was 10.4% in Chinese chickens, whereas ALVE21 was detected with a frequency of 0% in WL1 and 50% in WL2. The frequency of the TVB resistance allele ( TVB*R and TVB*R') was 0.4% in Beijing You chickens, whereas it was 70.5% in WL1 and 54.5% in WL2. No carriers of ALVE3, ALVE9, and ALVE21 were detected in Silkie fowl, a famous Chinese native breed that has been used as a source for alternative medicine. These results present molecular evidence of ALVE3, ALVE6, ALVE9, and ALVE21 insertions and TVB genotypes in Chinese indigenous chickens and could provide potential molecular insights into anti-ALV breeding in chickens.