ATF3 regulates Tiam2 expression during neutrophil development. (A) RNA from WT (white bars) or ATF3^−/− (black bars) neutrophils were analyzed by qRT-PCR for Tiam2 or Tiam1 expression. Representative of 3 independent experiments; N = 2 to 6 mice/genotype. Statistics are unpaired 2-tailed Student t test. (B) The −3-kb region of Tiam2 variant 1 (NM_011878) shown with the consensus ATF3 binding site TGA CGC CA (pink box) indicated relative to the known transcriptional activator NF-kB binding site (green box). (C) mRNA expression of Tiam2 during differentiation of WT myeloid progenitors (c-Kit⁺Lineage⁻ BM cells) to mature neutrophils. Bar graph shows Tiam2 expression at indicated time in culture. (D) Immunoblot of Tiam2 protein expression during WT LK differentiation as in C. (E) Immunoblot of Tiam2 protein expression in WT and ATF3^−/− neutrophils.