NOVEL ALLELES OF ANTIGEN PROCESSING GENES IN RAY-FINNED FISHES
Dustin Wcisel, Vanderbilt University School of Medicine
Dustin J. Wcisel1, Alex Dornburg2, Andrew Thompson3, Ingo Braasch3, and Jeffrey A. Yoder1
1. Department of Molecular Biomedical Sciences, North Carolina State University, Raleigh, NC USA
2. North Carolina Museum of Natural Sciences, Raleigh, NC USA
3. Department of Integrative Biology, Michigan State University, Lansing, MI USA
The inducible proteasome subunit (PSMB) genes are part of the 20S proteasome complex, responsible for systematically degrading proteins into small polypeptides for loading and display on major histocompatibility (MHC) proteins. In the genomes of teleost species such as zebrafish, the PSMB genes are clustered together adjacent to their MHC Class I counterparts. Within a given species, alternative haplotypes for these genes have been described. For example, the 31st amino acid residue of the PSMB8 mature protein is found to contain either an alanine or a phenylalanine (PSMB8A or PSMB8F, respectively). The sequence differences may lead to functional changes in the types of proteins degraded and thus the antigens displayed. These alternative alleles are present in Senegal bichir (Polypterus senegalus), and numerous teleost species as well as many tetrapods (Xenopus tropicalis for example). This type of conserved haplotypic variation is referred to as trans-species polymorphism. Recently, the genome sequencing of two holostean species, spotted gar (Lepisosteus oculatus) and bowfin (Amia calva) were completed. Here, we present the annotation of the PSMB loci in both species using the zebrafish genome as a reference point. We found the holostean PSMB8 gene, while highly conserved with other fish species, encodes novel alleles containing either a threonine or serine at the 31st residue. Many additional polymorphisms were also identified in the neighboring genes, suggesting holosteans experienced unique co-evolution of these genes at this locus likely resulting in functional differences of antigen presentation.