The UT family of MHC class I loci unique to non-eutherian mammals has limited polymorphism and tissue specific patterns of expression in the opossum.

Katina V Krasnec,Robert D Miller,Anthony T Papenfuss

doi:10.1186/s12865-016-0181-9

Abstract

BackgroundThe Major Histocompatibility Complex (MHC) class I family of genes encode for molecules that have well-conserved structures, but have evolved to perform diverse functions. The availability of the gray, short-tailed opossum, Monodelphis domestica whole genome sequence has allowed for analysis of MHC class I gene content in this marsupial. Utilization of a novel method to search for MHC related domain structures revealed a previously unknown family of MHC class I-related genes. These genes, named UT1-17, are clustered on chromosome 1 in the opossum, unlinked to the MHC region. UT genes are only found in marsupial and monotreme genomes, consistent with being ancient in mammals yet lost in eutherian mammals. This study investigates the expression and polymorphism of the UT loci in the opossum to gain insight into their possible function.ResultsOf the 17 opossum UT genes, most have restricted tissue transcription patterns, with the thymus and skin being the most common sites. Full-length structure of 11 UT transcripts revealed genes varying between five and eight exons, typical for class I family members. There were only two alternative splice variants found. The UT genes also have limited polymorphism and little evidence of positive selection. One locus, UT8, was chosen for further analysis due to its conservation amongst marsupials and generic characteristics. UT8 transcription is limited to developing αβ thymocytes, and is absent from mature αβ T cells in peripheral lymphoid tissues.ConclusionThe overall characteristics and features of UT genes including low polymorphism and restricted tissue expression make it likely that the molecules encoded by UT genes perform roles other than antigenic peptide presentation.Electronic supplementary materialThe online version of this article (doi:10.1186/s12865-016-0181-9) contains supplementary material, which is available to authorized users.

Highlights

The Major Histocompatibility Complex (MHC) class I family of genes encode for molecules that have well-conserved structures, but have evolved to perform diverse functions
The initial role for MHC class I proteins uncovered was the presentation of antigenic peptides to cytotoxic, CD8+ T cells [5]
For all other adult tissues, the colon and thyroid contained the greatest variety of transcribed ModoUT genes with four each

Summary

Introduction

The Major Histocompatibility Complex (MHC) class I family of genes encode for molecules that have well-conserved structures, but have evolved to perform diverse functions. Utilization of a novel method to search for MHC related domain structures revealed a previously unknown family of MHC class I-related genes. These genes, named UT1-17, are clustered on chromosome 1 in the opossum, unlinked to the MHC region. The Major Histocompatibility Complex (MHC) class I gene family encodes cell surface proteins that share a unique, well-conserved structure. In spite of the conserved structure, MHC class I molecules have evolved to perform a diverse set of functions. Antigenic peptides derived from proteolysis of self or pathogen derived proteins are bound in the groove created by the α1 and α2 domains and “presented” to CD8+ T cells by forming a ligand for the T

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