Novel sequences of subgroup J avian leukosis viruses associated with hemangioma in Chinese layer hens

Abstract

Background: Avian leukosis virus subgroup J (ALV-J) preferentially induces myeloid leukosis (ML) in meat-type birds. Since 2008, many clinical cases of hemangioma rather than ML have frequently been reported in association with ALV-J infection in Chinese layer flocks.

Results: Three ALV-J strains associated with hemangioma were isolated and their proviral genomic sequences were determined. The three isolates, JL093-1, SD09DP03 and HLJ09MDJ-1, were 7,670, 7,670, and 7,633 nt in length. Their gag and pol genes were well conserved, with identities of 94.5-98.6% and 97.1-99.5%, respectively, with other ALV-J strains at the amino acid level (aa), while the env genes of the three isolates shared a higher aa identity with the env genes of other hemangioma strains than with those of ML strains. Interestingly, two novel 19-bp insertions in the U3 region in the LTR and 5' UTR, most likely derived from other retroviruses, were found in all the three isolates, thereby separately introducing one E2BP binding site in the U3 region in the LTR and RNA polymerase II transcription factor IIB and core promoter motif ten elements in the 5' UTR. Meanwhile, two binding sites in the U3 LTRs of the three isolates for NFAP-1 and AIB REP1 were lost, and a 1-base deletion in the E element of the 3' UTR of JL093-1 and SD09DP03 introduced a binding site for c-Ets-1. In addition to the changes listed above, the rTM of the 3' UTR was deleted in each of the three isolates.

Conclusion: Our study is the first to discovery the coexistence of two novel insertions in the U3 region in the LTR and the 5' UTR of ALV-J associated with hemangioma symptoms, and the transcriptional regulatory elements introduced should be taken into consideration in the occurrence of hemangioma.

Figure 1

Phylogenetic relationships of the three isolates and other strains including refenrence ALV-Js and other retroviruses based on U3 5' LTR (Figure 1A), 5' UTR (Figure 1B) and env gene (Figure 1C). Isolates marked with a black triangle are three isolates in our study, and strains marked with a black square are also hemangioma ALV-Js from GenBank

Figure 2

Comparision of transcriptional regulatory elements in the U3 region of reference strains. Shown are the sequences of U3 from HPRS-103 [5]. Sequences identical to HPRS-103 are showed as dot (.) and the deletions are represented by dashes (-).The 19 bp novel insertion in the three isolates is marked and transcriptional regulatory elements in U3 area are boxed

Figure 3

Phylogenetic analysis of ALV-Js and other retroviruses based on 5' UTR.

Figure 4

Sequence comparison of E element of hemangioma ALV-Js with the prototype ML ALV-J strain HPRS-103. 1-bp deletion was coloured by grey background