Inhibitory receptor that acts as a critical regulator of hematopoietic lineage differentiation, megakaryocyte function and platelet production (PubMed:23112346). Inhibits platelet aggregation and activation by agonists such as ADP and collagen-related peptide (By similarity). 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:23112346). Appears to operate in a calcium-independent manner (By similarity). Interacts (via ITIM motif) with PTPN6 and PTPN11 (PubMed:23112346). Binds to heparin (By similarity). Expressed in mature megakaryocytes and platelets. Not expressed by immature megakaryocytes. Contains 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. N-glycosylated. May be O-glycosylated. Phosphorylated. Mutant mice exhibit macrothrombocytopenia (reduced platelet numbers and the presence of enlarged platelets) and a susceptibility to bleeding because of defective platelet production and function. They show an increased platelet turnover leading to reduced platelet numbers. Their megakaryocytes exhibit reduced integrin-mediated functions, defective formation of proplatelets as well as an increased metalloproteinase production.