Identification of natural killer cell receptor clusters in the platypus genome reveals an expansion of C-type lectin genes
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Natural killer (NK) cell receptors belong to two unrelated, but functionally analogous gene families: the immunoglobulin superfamily, situated in the leukocyte receptor complex (LRC) and the C-type lectin superfamily, located in the natural killer complex (NKC). Here, we describe the largest NK receptor gene expansion seen to date. We identified 213 putative C-type lectin NK receptor homologs in the genome of the platypus. Many have arisen as the result of a lineage-specific expansion. Orthologs of OLR1, CD69, KLRE, CLEC12B, and CLEC16p genes were also identified. The NKC is split into at least two regions of the genome: 34 genes map to chromosome 7, two map to a small autosome, and the remainder are unanchored in the current genome assembly. No NK receptor genes from the LRC were identified. The massive C-type lectin expansion and lack of Ig-domain-containing NK receptors represents the most extreme polarization of NK receptors found to date. We have used this new data from platypus to trace the possible evolutionary history of the NK receptor clusters.
KeywordsNKC Platypus Natural killer receptors Evolution Gene expansion Immune
This work was carried out as part of the Platypus Genome Project. We thank Wes Warren and his team at Washington University, St. Louis, for giving us the opportunity to work on such an exciting project. We thank Kaighan McColl for bioinformatics support. E.W. and C.S. receive scholarships from the Jean Walker Trust and the ARC Center for Kangaroo Genomics.
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