No effect of Egr-1 deficiency on mast-cell maturation was observed. Bone marrow cells from wild-type mice or Egr-1–deficient mice were cultured in conditioned media in vitro for 5 weeks and examined by flow cytometry for c-kit and IgE receptor expression (A) or by toluidine blue staining (B) Original magnification, × 100. Egr-1–deficient or wild-type mast cells express similar levels of c-kit and IgE receptor and show similar levels of granulation. (C) Tongue tissues from wild-type mice or Egr-1–deficient mice were fixed and stained by Alcian blue for mast cells. Similar metachromatic staining between wild-type and Egr-1–deficient tissues was observed. Original magnification, × 40. Specimens were viewed on a Nikon Eclipse E600 microscope equipped with a DMX1200 camera, a CFI Plan-Fluor DDL 100 ×/1.30 oil-immersion objective lens (B), and a DDL 40 ×/0.75 objective lens (C). Acquisition was performed with Nikon ACT-1 software version 2.20. Images were processed using Adobe Photoshop 5.0.