Looping interactions involving TAL1 promoters and enhancers in erythroid and lymphoid cells. (A) Schematic organization of the human and murine TAL1 loci. Locations and directions of transcription of TAL1 and its flanking genes PDZK1IP1, STIL, and CMPK1 are shown (horizontal gray arrows). Locations of promoters (vertical black arrows) and enhancers of the TAL1 gene studied here (vertical gray arrows) are shown. The erythroid and the stem cell enhancers are highlighted. Elements are named according to their distance (in kb) from TAL1 promoter 1a. Looping interactions tested in this study are denoted by dotted gray lines with arrowheads. (B) Bar diagram of interaction patterns across the human TAL1 locus in erythroid (K562) and lymphoid (HPB-ALL) cell lines determined by 3C. (C) Bar diagrams of interaction patterns across the murine Tal1 locus in primary erythroblasts (Erythroid) and lymphocytes (Lymphoid) determined by 3C. Interactions, measured as relative ligation frequencies (black bars) at various locations across the locus, are shown with standard errors (SEs). Location of 3C “bait” region (TAL1 promoter 1b = P^TAL1; P^Tal1 in mouse) is shown (vertical gray arrows). P values are indicated for relative ligation frequencies which are significantly higher for test regions when compared with those of control regions (controls defined as regions located between the “bait” and test regions). Scales (in kb) are shown at the bottom of panels B-C. (D) Comparison of interaction patterns at the TAL1 locus in human and murine cell types normalized against ERCC3 ligation frequencies. (Left panel) Human K562 and HPB-ALL cell lines. (Right panel) Primary murine erythroblasts and lymphocytes. P values are indicated for interactions which are significantly higher in the TAL1-expressing cell type. *P < .05; **P < .01; ***P < .001; ****P < .0001.