One example is the CCCTC-binding factor (CTCF), which regulates various cellular processes and has recently been shown to affect nuclear structure by binding to insulator sequences, preventing crosstalk between neighboring sequences, and facilitating chromatin loops between CTCF binding elements [ 146].
DNA methylation can affect transcription factor binding sites, insulator elements, and chromatin conformation, resulting in multiple levels of control of expression (reviewed in (Jones, 2012)).
Another possibility to overcome positional effects over the transgene is to use insulator elements within the plasmid carrying the hsp70 Gal80-Myc hsp70 Gal80-Myc
The Su(Hw) protein has been found to bind an insulator element within a gypsy retrotransposon to mediate enhancer-blocking of gypsy towards target genes [ 61, 62].
Transcription factors (TFs) regulate gene transcription by binding to specific DNA elements such as promoters, enhancers, silencers, insulators and locus control regions.
The mutation did, however, affect CP190 recruitment to specific Drosophila insulator elements and had a modest effect on dCTCF chromatin association.
However, there was no enrichment of CUX1 binding sites in proximity of insulator elements (Table 3).
CTS mutation results in hypermethylation of the H19 IC in the mouse, indicating that CTCF binding is required to maintain the insulator element hypomethylated and functional on the maternal chromosome [2].
In flies, dCTCF binds to the Fab-8 insulator element between iab-7 and iab-8 [ 75].
A number of mechanisms have been demonstrated to restrict the activity of a CRM to a particular promoter, including insulator elements [ 11], insulator-bypass or promoter targeting elements [ 12, 13], short-range repression [ 14], chromatin-mediated silencing [ 11, 15], and preferential interaction with promoters containing certain core promoter motifs [ 10, 16- 19].
