Genes of the chicken controlling cell susceptibility to infection with Avian Leukosis Sarcoma virus subgroups

R.K. Chaurasia, Bhukya Prakash, P.V.K. Sasidhar
Department of Genetics and Animal Breeding
College of Veterinary and Animal Sciences G.B.P.U.A.T., Pantnagar - 263145 (U.A.)

The inheritance of resistance to the different subgroups of Avian Leukosis Sarcoma (ALS) viruses has been analyzed by the segregation ratios of susceptible and resistance progenies in F 1, F 2 and back cross generations between two contrasting lines of chicken that differ significantly to infection. ALS viruses enter the cell through specific receptor on the cell surface. These receptors are determined by autosomal genetic loci that have dominant susceptibility and recessive resistance alleles. As per the earlier reports, the genes that control the cell susceptibility to infection with different virus subgroups of ALS virus are as follows: Subgroup A virus is controlled by tva (tumour virus a) locus carries a s (susceptible) and a r (resistant) alleles. Subgroup B and D viruses are controlled by tvb (tumour virus b) locus carries b s1, b s2, b s3 (susceptible) and b r (resistant) alleles. Virus subgroup C is controlled by tvc (tumour virus c) locus carries c s (susceptible) and c r (resistant) alleles and subgroup E is controlled by tve and I e loci, of which tve (tumour virus e) locus carries e s (susceptible) and e r (resistant) alleles and I e locus carries dominant resistant allele, I e and recessive susceptibility allele, i e. The loci tva, tvb, tvc and tve all carries dominant susceptibility alleles and recessive resistance alleles. Based on chorioallantoic membrane ( CAM) and liver tumour (LT) assay and on the occurrence of four types of tumour phenotypes i.e. CAM (+) LT (+), CAM (-) LT(-), CAM (+) LT(-) and CAM (-) LT(+), a 4-allele model has been proposed recently for tva and tvc loci. According to this tva locus carries four alleles, two susceptibility alleles (a s1 and a s2) and two resistance alleles (a r1 and a r2) and 10 genotypes. Similarly, tvc locus also carries four alleles, two susceptibility alleles (c s1 and c s2) and two resistance alleles (c r1 and c r2) and 10 genotypes. Analysis for possible gene association was carried out by calculating the frequencies of a r, b r and c r genes from the observed frequencies. Results showed that alleles at tva and tvb loci, likewise at tvb and tvc loci had recombined randomly, while those at tva and tvc loci had not. Hence, concluded the linkage between tva and tvc loci. Viruses of subgroup B and D are closely related in envelope properties and inheritance pattern, leading to a possible pleiotropic control of subgroup D response by the B-receptor coded for by the tvb gene. Considering the other genes, it has been reported that the black plumage colour gene (i+) reduced subgroup C susceptibility by four folds as compared to white plumage gene (I). The slow-feathering gene (K) has been associated with increased congenital and horizontal transmission of Avian Leukosis viruses (ALV). Expression of ev21 gene, which is linked to the K gene, may lead to partial immunological tolerance, and hence greater expression of exogenous ALV infection.

Source : IPSACON-2005

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