8. The gene DNMT1 encodes a DNA methyltransferase that plays a role in the methylation of CpG islands. This gene is over-expressed in some types of cancers. To understand its role in cancer development, cells were isolated from cancers with DNMT1 over-expression. Researchers used CRISPR to silence the DNMT1 gene in these cancer cells. This led to a re-expression of tumor suppressor genes, which were not expressed before silencing of the DNMT1 gene. Explain these results