Neural epithelial cell lysates were clarified from sonicated nuclei and SOX21 complexes or b-catenin-DNA complexes were immunoprecipitated with SOX21 antibody (R&D AF3538) or b-catenin antibody (BD Biosciences, 610154), respectively. Protein A and G Magnetic Dynabeads were used to capture antibody-bound protein-DNA complexes. The ChIP-enriched DNA samples were treated with end-repair of the DNA, adding “A” bases to the DNA, ligating sequencing adapters to DNA fragments, amplifying adapter-modified DNA by PCR and gel purification for ChIPseq using NEBNext Ultra DNA Library Prep Kit for Illumina. Purified libraries were sequenced on Illumina HiSeq X-ten platforms.