However, as expression of individual L1 elements is highly dependent on cellular context, as seen in various mouse tissues (33) and human cell lines (22,32) (Figure 1), our data demonstrate that a wide array of cancer-specific changes, including sequence rearrangements repositioning CTCF binding sites, individual interactions between L1 elements and their enhancers, or changes in RNA Pol II recruitment through transcriptional factors, influence expression of individual L1 loci. The gene discussed is CTCF; the disease is cancer.