Bovine Leukemia Virus

Genotypes and microRNAs

This page will cover everything you need to know about what has been discovered about the genetics surrounding BLV. Not only will this include what is traditionally thought of when hearing the word genetics, genotypes and potential markers, but also microRNAs. 

This research is on-going and there is still much to be learned! 

BoLA Allele Associations

What is BoLA?

BoLA is the abbreviation for the Bovine Leukocyte Antigen gene, which is another name for the bovine major histocompatibility complex. It is an important and diverse DNA region responsible for proper immune function. Research suggests that some versions of the gene are associated with BLV resistance, defined as maintaining a low amount of virus even after prolonged BLV infection. Conversely, other versions of this gene may increase susceptibility to BLV infection. As research to determine genetic associations related to BLV resistance advances, selection of breeding stock to aid in lowering BLV prevalence within a herd may be possible.

BoLA is composed of many loci, or regions within the gene. Loci within the BoLA gene are organized by generalized clusters known as classes (class I, IIa, IIb, and III). So far, associations with BLV are with alleles that exist in Class IIa's DRB3 and DQA loci. 

What do we know so far?

Associations between BoLA alleles and BLV have yet to be established in beef cattle, but there have been a number of studies in dairy cattle. 

•  BoLA-DRB3*0902 is the most consistently reported allele with 5 studies identifying it to be associated with BLV resistance. (Juliarena et al., 2008; Miyasaka et al., 2012; Hayashi et al., 2017; Takeshima et al., 2019; Lo et al., 2020)
• Additional alleles have also been identified as being associated with BLV resistance but less consistently. These include: BoLA-DRB3*1001, BoLA-DRB3*0201, BoLA-DRB3*14011, BoLA-DQA1*0204, BoLA-DQA1*1402, and BoLA-DQA1*12011 (Juliarena et al., 2008; Miyasaka et al., 2012; Miyasaka et al., 2013; Hayashi et al., 2017; Takeshima et al., 2019)
• There have been a few alleles identified as being associated with BLV susceptibility including: BoLA-DRB3*1501, BoLA-DRB3*1601, BoLA-DRB3*1201, BoLA-DQA1*10012 (Miyasaka et al., 2012; Miyasaka et al., 2013; Takeshima et al., 2019).

Host and Viral microRNAs 

Host miRNAs

Host miRNAs are microRNAs that originate from the animal genome. 

In 2017, seven microRNAs were found to be up-regulated in cows that tested positive for BLV antibodies (Taxis & Casas, 2017). The MSU BLV research team continues to look for associations between BLV, microRNAs, and their associated gene expression profiles. 

Viral miRNAs

Viral miRNAs are microRNAs that originate from the viral genome. 

• Bovine Leukemia virus encodes for five viral microRNAs: BLV-miR-B1, BLV-miR-B2, BLV-miR-B3, BLV-miR-B4, and BLV-miR-B5 (Kincaid, Burke, & Sullivan, 2012). You can read the study, here.
• In the same study, Kincaid, Burke, & Sullivan found that BLV-miR-B4 matches the sequence of the host microRNA miR-29. Both of these microRNAs are associated with B-cell tumor growth in mice. 
• Little is known about the function of these microRNAs, but there is evidence suggesting that BLV microRNAs alter gene expression in the host promoting viral replication in B-cells and aids in tumor development (Gillet et al., 2016). You can read the study, here.