Bridging multiple dimensions: roles of transposable elements in higher-order genome regulation.

Transposable elements (TEs) such as endogenous retroviruses (ERVs), long interspersed nuclear elements (LINEs), and short interspersed nuclear elements (SINEs) occupy nearly half of typical mammalian genomes. Previous studies show that these parasitic elements, especially LINEs and ERVs, provide important activities promoting host germ cell and placental development, preimplantation embryogenesis, and maintenance of pluripotent stem cells. Despite being the most numerically abundant type of TEs in the genome, the consequences of SINEs on host genome regulation are less well characterized than those of ERVs and LINEs. Interestingly, recent findings reveal that SINEs recruit the key architectural protein CTCF (CCCTC-binding factor), indicating a role of these elements for 3D genome regulation. Higher-order nuclear structures are linked with important cellular functions such as gene regulation and DNA replication. SINEs and other TEs, therefore, may mediate distinct physiological processes with benefits to the host by modulating the 3D genome.