title: Assessing the roles of endogenous retrovirus EAV-HP in avian leukosis virus subgroup J emergence and tolerance.
abstract: Avian leukosis virus (ALV) subgroup J is thought to have emerged through a recombination event between an unknown exogenous ALV and the endogenous retrovirus elements designated EAV-HP. All EAV-HP elements identified to date in the chicken genome show large deletions, including that of the entire pol gene. Here we report the identification of four segregating chicken EAV-HP proviruses with complete pol genes, one of which shows exceptionally high sequence identity and a close phylogenetic relationship with ALV-J with respect to the env gene. Embryonic expression of EAV-HP env has been suggested as a factor associated with immunological tolerance induction in a proportion of ALV-J-infected meat-type chickens. In support of this, env gene transcripts expressed from two of the four newly identified EAV-HP proviruses were demonstrated in chicken embryos. However, when ALV-J-infected outbred meat-type chickens were assessed, the presence of intact EAV-HP proviruses failed to directly correlate with ALV-J tolerance. This association was further examined using F(2) progeny of two inbred lines of layer chicken that differed in EAV-HP status and immunological responses to ALV-J. Immunological tolerance developed in a small proportion of F(2) progeny birds, reflecting the expected phenotypic ratio for inheritance of a double-recessive genotype; however, the status of tolerance did not show any direct correlation with the presence of the intact EAV-HP sequence. Nevertheless, identification of an intact chicken EAV-HP locus showing a uniquely close relationship to the ALV-J prototype clone HPRS-103 in the env region provides the strongest evidence of its contribution to the emergence of ALV-J by recombination.
authors.affiliation: Institute for Animal Health, Compton, Newbury, Berkshire, United Kingdom. mas289@cornell.edu
authors.forename: Melanie A
authors.initials: MA
authors.lastname: Sacco
authors.forename: Ken
authors.initials: K
authors.lastname: Howes
authors.forename: Lorraine P
authors.initials: LP
authors.lastname: Smith
authors.forename: Venugopal K
authors.initials: VK
authors.lastname: Nair
mesh_terms: D000818:Animals; D001353:Avian Leukosis / Q000276:immunology / Q000821:virology*; D001354:Avian Leukosis Virus / Q000145:classification / Q000235:genetics* / Q000276:immunology; D001483:Base Sequence; D002642:Chick Embryo; D002645:Chickens / Q000821:virology*; D004279:DNA, Viral / Q000737:chemistry / Q000302:isolation & purification; D020077:Endogenous Retroviruses / Q000235:genetics* / Q000276:immunology; D019143:Evolution, Molecular; D015967:Gene Expression Regulation, Viral; D015752:Genes, env; D015751:Genes, pol; D008969:Molecular Sequence Data; D010802:Phylogeny; D011533:Proviruses / Q000235:genetics*; D012333:RNA, Messenger / Q000032:analysis / Q000302:isolation & purification; D012367:RNA, Viral / Q000032:analysis / Q000302:isolation & purification; D011995:Recombination, Genetic; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D012689:Sequence Homology, Nucleic Acid
chemical_list: D004279:DNA, Viral; D012333:RNA, Messenger; D012367:RNA, Viral