Insulators: many functions, many mechanisms

Eukaryotic genomes are organized into domains containing individual genes and gene clusters that have distinct patterns of expression both during development and in differentiated cells. These genomes contain regulatory elements such as enhancers that are able to activate target genes in cis over considerable distances. They may also contain extended regions of condensed chromatin capable of encroaching on adjacent domains to perturb gene expression. There are a number of ways in which individual domains could be maintained independent of their surroundings through the establishment of boundaries. These boundaries might be variable in position, and established through a balance between countervail