Molecular cloning, gene structure, and expression pattern of pig immunoreceptor DAP12

Natural killer (NK) cells express receptors for MHC class I that contain im munoreceptor tyrosine-based inhibitory motif (ITIM) sequences in their cyto plasmic domain. Whereas these receptors inhibit NK cell cytotoxicity, certa in isoforms of these NK receptors (e.g., KIR2DS, CD94/NKG2C, and Ly49D) do not have ITIMs, but associate with DAP12 and activate NK cell function. We cloned pig DAP12 cDNA from a pig peripheral blood lymphocyte (PBL) cDNA lib rary using human DAP12 cDNA as a probe. The length of the pig DAP12 cDNA is 526 bp and contains an open reading frame of 324 bp. It has 79% identity w ith the human DAP12 cDNA sequence in the coding region and 73% identity wit h mouse DAP12 cDNA. The predicted polypeptide sequence of pig DAP12 is 108 amino acids, being composed of a 23-amino acid leader, a 14-amino acid extr acellular domain, a 24-amino acid transmembrane segment, and a 47-amino aci d cytoplasmic region. The amino acid sequence of pig DAP12 has 74% and 71% sequence identity with human DAP12 and mouse DAP12, respectively. Pig DAP12 has a conserved aspartic acid in the transmembrane region, and two conserv ed cysteine residues in the extracellular domain. It also contains an immun oreceptor tyrosine-based activation motif sequence in the cytoplasmic regio n. Genomic organization reveals that pig DAP12 consists of five exons and f our introns. Southern blot analysis of pig genomic DNA revealed that DAP12 is a single-copy gene. In Northern blot analysis, DAP12 transcripts were de tected in spleen, liver, thymus, and lymph node. DAP12 transcripts are expr essed not only in PBLs, but also in granulocytes, macrophages, and monocyte s.