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Phospholipase Cγ2 Dosage Is Critical for B Cell Development in the Absence of Adaptor Protein BLNK1

B cell linker (BLNK) protein and phospholipase Cγ2 (PLCγ2) are components of the BCR signalosome that activate calcium signaling in B cells. Mice lacking either molecule have a severe but incomplete block in B lymphopoiesis. In this study, we generated BLNK−/−PLCγ2−/− mice to examine the effect of simultaneous disruption of both molecules on B cell development. We showed that BLNK−/−PLCγ2−/− mice had compounded defects in B cell maturation compared with either single mutant, suggesting that these two molecules cooperatively or synergistically signaled B lymphopoiesis. However, Ig H chain allelic exclusion was maintained in single and double mutants, indicating that signals propagated by BLNK and PLCγ2 were not involved in this process. Interestingly, in the absence of BLNK, B cell development was dependent on plcγ2 gene dosage. This was evidenced by the proportionate decrease in splenic B cell population and increase in bone marrow surface pre-BCR+ cells in PLCγ2-diploid, -haploid, and -null animals. Intracellular calcium signaling and ERK activation in response to BCR engagement were also proportionately decreased and delayed, respectively, with stepwise reduction of plcγ2 dosage in a BLNKnull background. Thus, these data indicate the importance of BLNK not only as a conduit to specifically channel BCR-signaling pathways and as a scaffold for the assembling of macromolecular complex, but also as an efficient aggregator or concentrator of PLCγ2 molecules to effect optimal signaling for B cell generation and activation.