Btk and phospholipase Cγ2 can function independently during B cell development

The pre-BCR and the BCR regulate B cell development via a signalosome nucleated by the adaptor protein B cell linker protein (BLNK). Formation of this complex facilitates activation of phospholipase C (PLC) γ2 by Bruton's tyrosine kinase (Btk). To determine whether Btk and PLCγ2 also have separate functions, we generated Btk–/–PLCγ2–/– mice. They demonstrated a block in development at the pre-B stage and increased pre-BCR surface expression. This phenotype was more severe than that of Btk–/– or PLCγ2–/– mice. Although both Btk and PLCγ2 were required for proliferation of splenic B cells in response to BCR cross-linking, they contributed differently to anti-IgM-induced phosphorylation of ERK. Btk–/– and PLCγ2–/– mice each had a reduced frequency of Igλ-expressing B cells and impaired migration of pre-B cells towards stromal cell-derived factor 1. However, the increase in pre-B cell malignancy that occurs in BLNK–/– mice in the absence of Btk was not observed in the absence of PLCγ2. Thus, Btk and PLCγ2 act both in concert and independently throughout B cell development.