Inhibitory receptor that acts as a critical regulator of hematopoietic lineage differentiation, megakaryocyte function and platelet production (PubMed:12665801, PubMed:17311996, PubMed:27743390). Inhibits platelet aggregation and activation by agonists such as ADP and collagen-related peptide (PubMed:12665801). This regulation of megakaryocate function as well as platelet production ann activation is done through the inhibition (via the 2 ITIM motifs) of the receptors CLEC1B and GP6:FcRgamma signaling (PubMed:17311996). Appears to operate in a calcium-independent manner (PubMed:12665801). Isoform B, displayed in this entry, is the only isoform to contain both a transmembrane region and 2 immunoreceptor tyrosine-based inhibitor motifs (ITIMs) and, thus, the only one which probably has a role of inhibitory receptor. Isoform A may be the activating counterpart of isoform B. Interacts (via ITIM motif) with PTPN6 and PTPN11 (PubMed:11544253, PubMed:23112346). Binds to heparin (PubMed:15848171). Expressed in platelets. Expressed in a restricted set of hematopoietic cell lines including the erythroleukemia cell line K-562 and the T-cell leukemia cell lines MOLT-4 and Jurkat. Not detected in the monocyte-like cell line U-937, the B-cell-like cell line Raji, the fibroblast cell lines TK and HeLa, or the natural killer cell lines NKL, NK 62 and YT. Isoform B, displayed in this entry, is the only one of the isoforms to contain both a transmembrane region and 2 copies of a cytoplasmic motif that is referred to as the immunoreceptor tyrosine-based inhibitor motif (ITIM). This motif is involved in modulation of cellular responses. The phosphorylated ITIM motif can bind the SH2 domain of several SH2-containing phosphatases. The 2 ITIM motifs of isoform B are required for the inhibition of CLEC1B and GP6:FCER1G signaling and platelet activation. All isoforms are N-glycosylated. Isoform E is O-glycosylated. Phosphorylated. The disease is caused by variants affecting the gene represented in this entry.