Mapping of Ikaros and RBPJ binding sites in the mouse T cell leukemia cell line T29

The transcription factor Ikaros represses Notch signaling. Since Ikaros and Notch treanscriptional mediator RBPJ both recognize sequences that contain the same core TGGGAA motif, it was hypothesized that Ikaros represses Notch signaling by targeting Notch response elements and competing with RBPJ for their binding. Here we used the mouse T-cell leukemia cell line T29 to compare the genomic binding profiles of Ikaros and RBPJ by ChIP-seq. Overall design: The T29 cell line is derived from a Ikaros-deficient T-cell leukemia (Dumortier et al, MCB 26, 209-220, 2006) and exhibits strong Notch activation. We performed two chip-seq experiments with an anti-RBPJ antibody to map RBPJ binding sites. To map Ikaros binding sites, we engineered a T29-derived cell line that expresses a fusion protein between Ikaros and the ligand binding domain of the estrogen receptor (Ik1-ER) which is activated by addition of 4-hydroxy-tamoxifen (4OHT). We used an anti-Ikaros antibody to map the sites bound by Ik1-ER after treatment of the cells with 4OHT. Sequencing were performed with the Illumina GAII sequencer as as single end 36 base pair reads.