Variation of AID expression during the cell cycle. (A) EGFP KI at the AICDA locus in BL2 cells. The AID–EGFP KI construct includes the EGFP sequence inserted in-frame in exon 5 at the 3′ end of the AID coding region and a hygromycin resistance (hygroR) gene flanked by loxP sites. Configuration of the targeted AICDA locus is depicted after Cre-mediated excision of the hygroR gene. (B) Expression of AID-EGFP throughout the cell cycle. 48 h after IL-4 addition (10 ng/ml), AID-EGFP KI BL2 cells were fractionated according to their cell cycle status using counterflow elutriation. Collected fractions were stained with propidium iodide and analyzed for both DNA content and AID-EGFP MFI. Data for fractions 12, 30, and 39 are shown in C. (C) Cell cycle analysis and AID-EGFP expression level of the BL2 KI cell line with and without IL-4, and of representative elutriated fractions, corresponding to the different phases of cell cycle: G1 (fr.12), S (fr. 30), and G2/M (fr. 39).
