Fig. 4. Brg1^fl/fl:Tie2-Cre^+/0 primitive erythroblasts have embryonic globin deficits. (A-H) Cryosections from an E9.5 control Brg1^fl/fl embryo (A,C,E,G) and a mutant Brg1^fl/fl:Tie2-Cre^+/0 embryo (B,D,F,H) were subjected to in situ hybridization with probes against embryonic and adult -globins and embryonic β-globins. Almost all embryonic blood cells from the control embryo express embryonic -globin (A), adult 1/2-globins (C), embryonic β-globin y (E) and embryonic βH1-globin (G). In the mutant embryo, adult 1/2-globin expression is normal (D), but many embryonic blood cells can be detected that express little or no embryonic (B), y (F) or βH1 (H), as indicated by the arrowheads in the respective insets. Scale bars: 40 µm. (I) Mean percentages of globin-expressing blood cells from multiple serial sections of two control and two mutant embryos at E9.5, as detected by in situ hybridization in three independent experiments. Total blood cells counted from control/mutant sections with each probe were: , 1521/907; 1/2, 1292/635; y; 977/721; and βH1, 492/818. Errors were calculated as s.e.m. (J) ChIP assay demonstrating that BRG1 is recruited to the β-globin LCR DNAse I hypersensitive site 3 (HS3) and the promoter in primitive erythrocytes. No evidence of BRG1 recruitment is detected at the 1/2 promoter. MW, 100 bp molecular weight standard; Pos, wild-type genomic DNA served as a positive control for the PCR; Neg, no DNA was amplified as a negative control; Input, total chromatin, sheared but not immunoprecipitated; Ac-H3, ChIP material immunoprecipitated with an antibody against pan-acetyl histone 3 (H3), a mark of an open chromatin structure; BRG1, ChIP material immunoprecipitated with an antibody against BRG1; Mock, mock immunoprecipitation in which the sample was not treated with antibody but was otherwise handled identically to the ChIP samples.