Expression and function of B cell specific MB-1 protein associated with IgM receptor

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We have previously identified a novel B cell specific gene named mb-1 that is expressed selectively in the restricted stage of B cell differentiation. In this project, we identified the B cell specific mb-1 gene product and found the association of the MB-1 protein with IgM receptor on the surface of B cells. To further characterize the expression and function of this molecule, we prepared rat monoclonal Ab against MB-1 protein on the cell surface. MB-1 is expressed already at the earliest stage in the B cell differentiation when IgM receptor ganes are with germ line configuration. Using mAbs, we demonstrated that MB-1 molecule itself is capable of mediating positive signals into B lineage cells in proliferation, increased Ca^<2+> concentration, and in tyrosne phosphorylation of intracellular proteins. These results suggested interesting but unknown functions of the IgR-associated molecules in the differentiation of early B lineage cells. We are currently started to analyze further function of MB-1 molecule in the experimental systems with DNA transfection, and gene targeting method.