Bcl-2 reduces mutant rates in a transgenic lacZ reporter gene in mouse pre-B lymphocytes

Abstract To assess mutagenesis during early B-lymphocyte development in vitro, progenitor B cells (pre-B cells) were obtained from fetal livers of BALB/c mice and DBA/2N mice that harbored the transgenic shuttle vector, pUR288, with a lacZ reporter gene for the determination of mutant frequencies (MFs). Differentiation-arrested pre-B cells demonstrated a marked dose-dependent increase in lacZ mutant levels after exposure to γ-irradiation with a peak MF of 250×10 −5 at 2.5 Gy. Without genotoxic treatment, pre-B cells undergoing spontaneous differentiation into surface IgM expressing immature B cells exhibited lacZ mutant levels of up to 95×10 −5 . The mutational pattern was dominated in both experiments by illegitimate recombination mutations of lacZ , not point mutations. Likewise, in both experiments, the enforced expression of Bcl-2 resulted in a striking reduction of lacZ mutations. These findings indicated that mouse pre-B cells are prone to accumulate induced and self-inflicted mutations, particularly recombinations. Additionally, our studies revealed a heretofore unknown role of Bcl-2 in inhibiting mutagenesis during early B-cell development in mice.