Tissue-specific loss and gain of expression in CD8B2 and maintenance of ancestral open-reading frame (ORF). (A) CD8B was duplicated in full (canonical isoform) from the p-arm to the q-arm of Chromosome 2, generating CD8B2. (B) We identify expressed transcripts from CD8BP that resemble those of CD8B and maintain the 210 aa ORF but with four amino acid replacements. (C) Tissue-specific expression estimates generated using Kallisto and GTEx RNA-seq data indicate that, relative to CD8B, CD8B2 has almost entirely lost expression in blood and gained expression in brain (cortex). Transcripts per million (tpm) plotted with log scale. (D) Single-cell RNA-seq data from T cells (10x Genomics) supports that CD8B2 expression has been lost specifically in T cells likely due to the duplication excluding a tissue-specific enhancer (see text). While multimap RNA-seq reads map to both paralogs because they lack singly unique nucleotides (SUNs) that distinguish the two, uniquely mapping reads from T cells map exclusively to ancestral CD8B.
