Phylogenetic analysis based on whole genome sequence of bovine leukemia virus in cattle under 3 years old with enzootic bovine leukosis

Abstract

Enzootic bovine leukosis (EBL) is one of bovine neoplasms caused by bovine leukemia virus (BLV). Although EBL is typically observed in cattle over 3 years old, several cases of EBL onset in cattle under 3 years old have been reported in Japan. The mechanism for EBL onset in young cattle remains unclear. Although genetic variation of BLV is limited, the variations could affect viral properties relating to BLV pathogenesis. The purpose of this study was to clarify relationship between early onset of EBL and BLV groups. Moreover, we also aimed to characterize BLV that cause early onset of EBL. Whole genome sequences of BLV in 72 EBL cattle under 3 years old and 50 EBL cattle over 3 years old were identified. Phylogenetic analysis showed that BLV was divided into 4 groups (A, B-1, B-2 and Other). The BLV from EBL cattle under 3 years old were mainly classified as group A and B-1, while those from EBL cattle over 3 years old were mainly included in group B-2. Common sequence of group A and B-1 was compared with those of group B-2. Specific sequences in LTRs, gag-pro-pol, env and tax gene regions were identified in these groups. Amino acid substitutions of Pro and Tax protein were predicted in those nucleotide sequences. Those genetic variations might contribute to the early onset of EBL.

Structural characteristics of the bovine leukemia virus genome: A mini review

“…Экспрессия вирусных генов индуцируется на транскрипционном уровне при помощи трансактиватора Tax, кодируемого вирусом [14]. Белок Tax функционирует как трансактиватор транскрипции вирусных генов и модулирует экспрессию некоторых клеточных генов хозяина [15]. Таким образом, считается, что белок Tax играет критическую роль в процессе лейкемогенеза, вызываемого дельтавирусами [16].…”

Enzootic bovine leukosis caused by bovine leukemia virus classified as Group C based on viral whole genome sequencing in a 23-month-old Holstein-Friesian heifer

“…BLV is divided into 5 groups (A, B-1, B-2, C, and other) according to its complete genome sequence. BLV in EBL cattle under 3 years of age is mainly classified as Group A or B-1 [ 5 , 11 ], and previous studies have reported no Group C strain in EBL cattle. In fact, Group C BLV has only been isolated from cattle without EBL [ 5 , 7 , 11 ].…”

“…BLV in EBL cattle under 3 years of age is mainly classified as Group A or B-1 [ 5 , 11 ], and previous studies have reported no Group C strain in EBL cattle. In fact, Group C BLV has only been isolated from cattle without EBL [ 5 , 7 , 11 ]. Here we report a clinical case of EBL caused by BLV classified as Group C in a 23-month-old Holstein-Friesian heifer with no enlargement of lymph nodes or masses in the pelvic cavity.…”

“…Several factors including polymorphisms of BoLA-DRB3 and BLV strain are related to lymphoma development in young cattle [ 5 , 6 ]. The BoLA-DRB3*015:01 allele was previously reported to be an early EBL onset susceptibility allele [ 6 ].…”

“…The BoLA-DRB3*015:01 allele was previously reported to be an early EBL onset susceptibility allele [ 6 ]. BLV is classified into 5 groups based on whole genome phylogenetic analysis, and the pathogenicity of Group C BLV is considered low [ 5 ]. In the present case, the genotype was identified as DRB3*007:01/015:01 , and findings from the phylogenetic analysis of the whole BLV genome were consistent with those of Group C BLV.…”