Journal Article

unique T cell receptor discovered in marsupials

Baker, Michelle L, Schwarz, Ryan S, Lindblad-Toh, Kerstin, Deakin, Janine E, Miller, Robert D, Parra, Zuly E

2007

Overview

T cells recognize antigens by using T cell receptors (TCRs) encoded by gene segments, called variable (V), diversity (D), and joining (J), that undergo somatic recombination to create diverse binding specificities. Four TCR chains (α, β, γ, and δ) have been identified to date, and, as T cells develop in the thymus, they express exclusively either an αβTCR or a γδTCR heterodimer. Here, we show that marsupials have an additional TCR (TCRμ) that has V, D, and J that are either somatically recombined, as in conventional TCRs, or are already prejoined in the germ-line DNA in a manner consistent with their creation by retrotransposition. TCRμ does not have a known homolog in eutherian mammals but has features analogous to a recently described TCRδ isoform in sharks. TCRμ is expressed in at least two mRNA isoforms that appear capable of encoding a full-length protein, both of which are transcribed in the thymus and spleen. One contains two variable domains: a somatically recombined V and a prejoined V. This appears to be the dominant isoform in peripheral lymphoid tissue. The other isoform contains only the prejoined V and is structurally more similar to conventional TCR chains, however invariant. Unlike other TCRs, TCRμ uses prejoined gene segments and is likely present in all marsupials. Its similarity to a TCR isoform in sharks suggests that it, or something similar, may be present in other vertebrate lineages and, therefore, may represent an ancient receptor system.

• Publisher: National Academy of Sciences,National Acad Sciences
• Subject: Amino Acid Sequence / Animals / Antigen / Antigens / Base Sequence / Biological Sciences / Cluster Analysis / DNA / Evolutionary biology / Exons / Gene Components / Genes / Genetic loci / Immune system / Immunoglobulin Variable Region - genetics / mammals / Marsupialia - genetics / Marsupialia - immunology / Marsupialia/genetics/immunology / Marsupials / MEDICIN / MEDICINE / messenger RNA / Messenger/genetics / Metatheria / Molecular Sequence Data / Phylogeny / Protein isoforms / Protein Isoforms - genetics / Receptors / Receptors, Antigen, T-Cell - genetics / RNA / RNA, Messenger - genetics / Sequence Alignment / Sequence Analysis / Sequence Analysis, DNA / Sharks / Species Specificity / Spleen / T cell antigen receptors / T cell receptors / T lymphocytes / T-Cell/genetics / thymus gland