POU5F1 and embryonal carcinoma: Reporter gene expression experiments in mouse with LacZ revealed that two elements, the proximal enhancer (PE) and the distal enhancer (DE) are essential in the cell-specific regulation of POU5F1. The proximal enhancer (PE) is located about 1.2 kb upstream, within conserved regions (CR2 and CR3) and is responsible for POU5F1 expression in embryonic ectoderm and mouse embryonal carcinoma (EC) cells.