Postmitotic G1 phase survivin drives mitogen-independent cell division of B lymphocytes

B and T lymphocytes of the adaptive immune system undergo proliferative bursts to generate pools of antigen-specific cells for effective immunity. Here we show that in contrast to the canonical view that G1 progression signals are essential after mitosis to reenter S phase, B lymphocytes sustain several rounds of mitogen-independent cell division following the first mitosis. Such division appears to be driven by unique characteristics of the postmitotic G1 phase that has features of S and G2/M phases. Birc5 (survivin), a protein associated with chromosome segregation in G2/M, is expressed in the G1 phase of divided B cells and is necessary for mitogen-independent divisions. The partially active G1 phase and propensity for apoptosis inherited after each division may underlie rapid proliferation and cell death, which are hallmarks of B cell proliferative responses.

Automated summary

Contrary to the traditional view, B lymphocytes can undergo multiple rounds of cell division independent of mitogens after the first mitosis, possibly due to unique characteristics of the postmitotic G1 phase resembling S and G2/M phases. Additionally, the expression of the Birc5 protein in the G1 phase of divided B cells plays a crucial role in apoptosis and rapid proliferation during B cell proliferation.