DNMT1 and colorectal cancer: In contrast to DNMT1, which maintains life-long expression in proliferative cells, DNMT3A and DNMT3B are expressed mainly during early embryogenesis (though they have some specialized functions in adulthood, such as maintaining self-renewal of hematopoietic stem cells (Tadokoro et al., 2007), cooperating with DNMT1 in silencing tumor suppressor genes in colorectal cancer cells (Rhee et al., 2002), or regulating synaptic plasticity in the brain (Feng et al., 2010a; LaPlant et al., 2010).