Abstract
Bats are natural hosts to numerous viruses and have ancient origins, having diverged from other eutherian mammals early in evolution. These characteristics place them in an important position to provide insights into the evolution of the mammalian immune system and antiviral immunity. We describe the first detailed partial map of a bat (Pteropus alecto) MHC-I region with comparative analysis of the MHC-I region and genes. The bat MHC-I region is highly condensed, yet relatively conserved in organisation, and is unusual in that MHC-I genes are present within only one of the three highly conserved class I duplication blocks. We hypothesise that MHC-I genes first originated in the β duplication block, and subsequently duplicated in a step-wise manner across the MHC-I region during mammalian evolution. Furthermore, bat MHC-I genes contain unique insertions within their peptide-binding grooves potentially affecting the peptide repertoire presented to T cells, which may have implications for the ability of bats to control infection without overt disease.
Highlights
The classical MHC-I sub-region contains a set of framework genes with highly conserved presence and order amongst all mammals[20,26,27]
The α duplication block is demarcated by MOG and RING finger protein 39 (RNF39), the κ duplication block by tripartite motif containing 26 (TRIM26) and ATP-binding cassette sub-family F member 1 (ABCF1), and the β duplication block by transcription factor 19 (TCF19) and MICB framework genes
Lower vertebrates, including teleost, Xenopus and chickens, have a conserved framework gene organisation but their MHC-I genes are not located within this framework; instead they are embedded within the class II region[28,29,30,31]
Summary
The classical MHC-I sub-region contains a set of framework genes with highly conserved presence and order amongst all mammals[20,26,27]. Class Ia molecules are ubiquitously expressed, highly polymorphic and present peptide to cytotoxic T cells. The presence of a unique insertion within the PBG of a number of the bat MHC-I molecules provides evidence for differences in the PBG, which may reflect functions other than antigen presentation or alternatively influence the size of peptides presented to cytotoxic T cells. To our knowledge, this is the first genomic map of a bat MHC-I region and characterisation of MHC-I genes of any bat species
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