Ikaros has a crucial role in regulation of B cell receptor signaling

transcription factor Ikaros, a key regulator of hematopoiesis, has an essential role in lymphocyte development. In mice, fetal lymphoid differentiation is blocked in the absence of Ikaros, and whereas T cells develop postnatally, B cells are totally absent. The significance of Ikaros in the B cell development is evident, but how Ikaros regulates B cell function has neither been established nor previously been studied with B cells that lack Ikaros expression. Here we show that disruption of Ikaros in the chicken B cell line DT40 induces a B cell receptor (BCR) signaling defect with reduced phospholipase C gamma 2 phosphorylation and impaired intracellular calcium mobilization, which is restored by Ikaros reintroduction. Furthermore, we show that lack of Ikaros induces hyperphosphorylation of Casitas B lymphoma protein subsequent to BCR activation. These results indicate that the absolute need of Ikaros for development, cell fate decisions and maintenance of B cells is due to the enhancement of BCR signaling.