Dual requirement for the Ig alpha immunoreceptor tyrosine-based activation motif (ITAM) and a conserved non-Ig alpha ITAM tyrosine in supporting Ig alpha beta-mediated B cell development.
Surface Ig (sIg) expression is a critical checkpoint during avian B cell development. Only cells that express sIg colonize bursal follicles, clonally expand, and undergo Ig diversification by gene conversion. Expression of a heterodimer, in which the extracellular and transmembrane domains of murine CD8alpha or CD8beta are fused to the cytoplasmic domains of chicken Igalpha (chIgalpha) or Igbeta, respectively (murine CD8alpha (mCD8alpha):chIgalpha + mCD8beta:chIgbeta), or an mCD8alpha:chIgalpha homodimer supported bursal B cell development as efficiently as endogenous sIg. In this study we demonstrate that B cell development, in the absence of chIgbeta, requires both the Igalpha ITAM and a conserved non-ITAM Igalpha tyrosine (Y3) that has been associated with binding to B cell linker protein (BLNK). When associated with the cytoplasmic domain of Igbeta, the Igalpha ITAM is not required for the induction of strong calcium mobilization or BLNK phosphorylation, but is still necessary to support B cell development. In contrast, mutation of the Igalpha Y3 severely compromised calcium mobilization when expressed as either a homodimer or a heterodimer with the cytoplasmic domain of Igbeta. However, coexpression of the cytoplasmic domain of Igbeta partially complemented the Igalpha Y3 mutation, rescuing higher levels of BLNK phosphorylation and, more strikingly, supporting B cell development.
Pike
Kelly A
KA
Department of Immunology, University of Toronto, Toronto, Ontario, Canada.
Ratcliffe
Michael J H
MJ
D048868:Adaptor Proteins, Signal Transducing; D020816:Amino Acid Motifs; D000818:Animals; D015703:Antigens, CD / Q000235:genetics / Q000502:physiology*; D001358:Avian Sarcoma Viruses / Q000235:genetics / Q000276:immunology; D001402:B-Lymphocytes / Q000166:cytology* / Q000276:immunology* / Q000378:metabolism; D051925:CD79 Antigens; D020013:Calcium Signaling / Q000235:genetics / Q000276:immunology; D002352:Carrier Proteins / Q000378:metabolism; D002454:Cell Differentiation / Q000276:immunology; D045744:Cell Line, Tumor; D002478:Cells, Cultured; D002642:Chick Embryo; D002645:Chickens; D017124:Conserved Sequence; D003593:Cytoplasm / Q000276:immunology / Q000378:metabolism; D019281:Dimerization; D051379:Mice; D016297:Mutagenesis, Site-Directed; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D017434:Protein Structure, Tertiary / Q000235:genetics; D011947:Receptors, Antigen, B-Cell / Q000235:genetics / Q000502:physiology*; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis / Q000502:physiology; D014443:Tyrosine / Q000235:genetics / Q000378:metabolism*
D048868:Adaptor Proteins, Signal Transducing; D015703:Antigens, CD; C113939:B cell linker protein; D051925:CD79 Antigens; D002352:Carrier Proteins; C497882:Cd79a protein, mouse; C497884:Cd79b protein, mouse; D010750:Phosphoproteins; D011947:Receptors, Antigen, B-Cell; D011993:Recombinant Fusion Proteins; D014443:Tyrosine