Combined deficiencies in Bruton tyrosine kinase and phospholipase Cγ2 arrest B-cell development at a pre-BCR+ stage

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Abstract
Bruton tyrosine kinase (Btk) and phospholipase Cγ2 (PLCγ2) are 2 key molecules involved in B-cell receptor (BCR) signaling. Biochemical studies have placed them in a linear signaling pathway, with Btk acting upstream of PLCγ2. Consistent with this, mice lacking either molecule display a leaky but similar block in B-cell development. Here, we generated Btk−/−PLCγ2−/− mice and showed that combined deficiencies in Btk and PLCγ2 severely arrested B lymphopoiesis at the large pre–B-cell stage. In contrast to either single mutant, Btk−/−PLCγ2−/− pre–B cells expressed high levels of pre-BCR on their cell surfaces and exhibited reduced immunoglobulin light chain gene rearrangements. Pre-BCR–induced calcium signaling was also drastically compromised in Btk−/−PLCγ2−/− pre–B cells compared with wild-type and single-mutant cells. Interestingly, immunoglobulin heavy chain allelic exclusion remained intact in the absence of Btk and PLCγ2. Overall, our results suggest that Btk and PLCγ2 have combinatorial roles in regulating pre–B cell differentiation.