Fig. 7.

Representative candidate bony fish NKRs. Predicted protein structures of select NITRs from zebrafish, NILTs from trout and LITRs from catfish. Ten different NITR forms are inferred from 39 different zebrafish gene sequences. Cross-linking inhibitory NITRs down-regulate the MAPK signal transduction pathway presumably via SHP-1 and SHP-2 (not shown). Activating NITRs associate with and signal through the adaptor protein Dap12 and, in the context of human NK cells, redirect cytolysis of target cells (in vitro). Six NILTs isoforms are encoded by four trout genes via alternative mRNA splicing. Neither a NILT ligand nor functional confirmation of NILT signaling has been reported. Certain ITIM-containing LITRs can associate with both SHP-1 and SHP-2 (not shown). Surface expression of certain activating LITRs is enhanced by cotransfection with Fcε RIγ and Fcε RIγ-like molecules. Fcε RIγ and Fcε RIγ-like proteins can be co-precipitated with activating LITRs. Although a CD3ζ-like adaptor protein can be co-precipitated with an activating LITR, its expression does not influence the surface expression of activating LITRs and is not shown. An asterisk (*) indicates that structures have been confirmed from EST or cDNA sequences. Proteins encoded by alternatively spliced transcripts are denoted with “sp”. C-type lectin domains (CTLDs), C2-type Ig domains (C2), positively-charged transmembrane residues (+), cytoplasmic immunoreceptor tyrosine-based inhibition motifs (ITIMs), ITIM-like sequences (itim), immunoreceptor tyrosine-based activation motifs (ITAM) and immunoreceptor tyrosine-based switch motifs (ITSM) are indicated. The classifications: LITR1-like and 2-like sequences are described in (Stafford et al. 2007).