Fig. 4

TEs function as insulators and modulators of the 3D chromatin conformation. A TE sequences facilitate the establishment of 3D chromatin structures in the nucleus, including the formation of nuclear speckles and nucleoli. B LINE1 serves as a seed to recruit heterochromatic proteins such as HP1a. HP1a and/or LINE1 transcripts may also attract each other and undergo a phase-separation mechanism from LINE1-enriched compartment B in the nucleolus. C Lamin also targets LINE1 sequences to form heterochromatin by the inner nuclear membrane. D SINEs serve as seeds to recruit euchromatic proteins such as Pol II to promote transcription. Pol II and/or SINE B1 transcripts may further attract each other and undergo a phase-separation mechanism from nuclear speckles (SINE-enriched nuclear compartment A), activating gene expression. E TEs also serve as insulators and attract some proteins, such as CTCF or Pol III, to block enhancer accessibility and insulate gene expression. F Mammalian-wide interspersed repeats (MIRs), which belong to the SINE family, can be targeted by Pol III to function as insulators