Fig. 1.

Asymmetric division of germinal center (GC) B cells. (A) Mitotic GC B cells from pooled spleens of 3 mice at d8 post-immunization stained for Bcl6, IL-21R, IRF4, or B220 (green), β-tubulin (red), and DNA (blue). Compared to tubulin, Bcl6 asymmetry 44%, n=16 mitoses, p<0.05; IL-21R asymmetry 43%, n=14, p<0.05; IRF4 asymmetry 11%, n=18, p>0.05; B220 asymmetry 11%, n=18, p>0.05. (B) Asymmetric mitoses of Bcl6 (filled) and tubulin (open) at d5, d8, d15 post-immunization, n=9, 16, 15, respectively, * = p<0.05. p values calculated with chi-squared tests. (C) Bcl6 and PKCζ co-segregate asymmetrically during mitosis at d8 post-immunization. Bcl6 and PKCζ were asymmetric in 44% and 38% of mitoses, respectively, and were 100% co-segregated when both were asymmetric, n=16 mitoses. (D) Isolated GC B cells undergoing cytokinesis maintain asymmetry. Bcl6, IL-21R, and PKCζ were asymmetric in 45%, 53%, and 61% of divisions, respectively, and had 100% co-segregation when both were asymmetric. Analysis of Bcl6 and IL-21R, n=13 cytokinetic cells; analysis of Bcl6 and PKCζ, n=13. All data are representative of 2 or more experiments.