Summary auto-generated
Researchers identified a novel endogenous avian retrovirus subfamily designated EAV-HP in chicken genomes that is closely related to HPRS-103, the prototype of avian leukosis virus (ALV) subgroup J. Using PCR amplification and Southern blotting, they demonstrated that EAV-HP sequences share 97% sequence identity with the HPRS-103 envelope gene, compared to only 40% identity with other ALV subgroups. EAV-HP sequences were present in all eight chicken lines examined and in grey jungle fowl, but absent from other avian species and mammals. The study identified six distinct EAV-HP loci distributed across multiple chicken chromosomes. Nucleotide sequence analysis confirmed that EAV-HP elements are distinct from the previously characterized EAV-0 family, though both show similar genomic distributions. The high sequence identity and the presence of a unique insertion sequence in the transmembrane domain suggest that HPRS-103 likely arose through recombination between exogenous virus sequences and these endogenous EAV-HP elements, representing the first documented avian example of an oncogenic retrovirus evolving from an endogenous counterpart.
Key findings
- A new subfamily of endogenous avian retroviruses (EAV-HP) was identified with 97% sequence identity to HPRS-103 ALV subgroup J envelope gene sequences
- EAV-HP elements are present in all chicken lines and grey jungle fowl examined but absent from other avian species and mammals
- Six distinct EAV-HP loci were mapped to chicken chromosomes 1, 3, 4, and W, distinct from EAV-0 loci positions
- HPRS-103 likely evolved through recombination between exogenous viral sequences and endogenous EAV-HP elements, the first known example of ALV subgroup evolution from endogenous counterparts
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Abstract
HPRS-103, the prototype of avian leukosis virus (ALV) subgroup J, is a recently identified retrovirus associated with myeloid leukosis in meat- type chickens. Although this virus shows high sequence identity to other ALV subgroups within the gag and pol genes, its env gene is highly diverged (with only about 40% sequence identity) from other ALV subgroups. On the other hand, the sequence of the env gene of HPRS-103 was 75% identical to that of E51, a member of the EAV family of endogenous avian retroviruses. It is reported here that the chicken genome also contains another EAV-related element, EAV-HP, showing much greater sequence identity (over 97%) to the HPRS-103 env gene. Southern blotting analysis showed that EAV-HP-related sequences were distinct from EAV-O and were present in all lines of chicken examined and in grey jungle fowl, but were absent from several other avian species. The potential role of these endogenous sequences in the evolution of ALV subgroup J viruses is discussed.