title: Co-expression of the collagen receptors leukocyte-associated immunoglobulin-like receptor-1 and glycoprotein VI on a subset of megakaryoblasts.
abstract: BACKGROUND
  The collagen receptor glycoprotein VI generates activating signals through an immunoreceptor tyrosine-based activating motif on the co-associated Fc receptor gamma chain. Leukocyte-associated immunoglobulin-like receptor-1 also ligates collagen but generates inhibitory signals through immunoreceptor tyrosine-based inhibitory motifs. Thus far, the cellular expression of glycoprotein VI and leukocyte-associated immunoglobulin-like receptor-1 appears mutually exclusive.
  
  
  METHODS
  Using flow cytometry, we studied expression of collagen receptors on differentiating human megakaryocytes. CD34(+) cells were isolated from umbilical cord blood and matured to megakaryocytes in vitro. Freshly isolated bone marrow cells were used to study primary megakaryocytes. Upon cell sorting, cytospins were made to examine cytological characteristics of differentiation.
  
  
  RESULTS
  Megakaryocyte maturation is accompanied by up-regulation of glycoprotein VI and down-regulation of leukocyte-associated immunoglobulin-like receptor-1. Interestingly, both in cultures from hematopoietic stem cells and primary cells obtained directly from bone marrow, we identified a subset of morphologically distinct megakaryocytes which co-express glycoprotein VI and leukocyte-associated immunoglobulin-like receptor-1.
  
  
  CONCLUSIONS
  This is the first report of a primary cell that co-expresses these collagen receptors with opposite signaling properties. Since megakaryocytes mature in the collagen-rich environment of the bone marrow, these findings may point to a role for leukocyte-associated immunoglobulin-like receptor-1 in the control of megakaryocyte maturation/migration.
authors: Department of Immunology, University Medical Center Utrecht, Utrecht, The Netherlands.
authors: Tessa A M
authors: TA
authors: Steevels
authors: Geertje H A
authors: GH
authors: Westerlaken
authors: Marloes R
authors: MR
authors: Tijssen
authors: Paul J
authors: PJ
authors: Coffer
authors: Peter J
authors: PJ
authors: Lenting
authors: Jan Willem N
authors: JW
authors: Akkerman
authors: Linde
authors: L
authors: Meyaard
mesh_terms: D018952:Antigens, CD34 / Q000378:metabolism; D001792:Blood Platelets / Q000378:metabolism*; D001854:Bone Marrow Cells / Q000378:metabolism; D045744:Cell Line, Tumor; D002478:Cells, Cultured; D005312:Fetal Blood / Q000166:cytology; D005434:Flow Cytometry; D006412:Hematopoietic Stem Cells / Q000378:metabolism; D006801:Humans; D038982:Integrin alpha2beta1 / Q000378:metabolism; D055016:Megakaryocyte Progenitor Cells / Q000378:metabolism*; D008533:Megakaryocytes / Q000378:metabolism; D039902:Multipotent Stem Cells / Q000378:metabolism; D010980:Platelet Membrane Glycoproteins / Q000378:metabolism*; D038981:Receptors, Collagen / Q000378:metabolism; D011971:Receptors, Immunologic / Q000378:metabolism*; D034061:Thrombopoiesis
chemical_list: D018952:Antigens, CD34; D038982:Integrin alpha2beta1; D010980:Platelet Membrane Glycoproteins; D038981:Receptors, Collagen; D011971:Receptors, Immunologic; C108073:leukocyte-associated immunoglobulin-like receptor 1; C098341:platelet membrane glycoprotein VI