Insulators

Insulators are boundary elements that prevent irrelevant enhancer and silencer action. They classify them into enhancer blockers and barriers. Insulator mutation or deletion affects gene expression patterns and causes a developmental defect. Insulators are elements that separate enhancers and suppressors to prevent any irrelevant action. They are further classified based on their function as enhancer blockers (located between cognate enhancer and promoter) and enhancer barriers, which are located between promoter and enhancer. CCCTC-binding factor (CTCF) is the most abundant protein associated with insulator activity. Example: CTCF acts as a positive regulator for the H19 gene while CTCF prevents the activation of Igf2 maternal allele via distal enhancer. CTCF also mediates insulator-insulator, enhancer-promoter and insulator-promoter interactions. Cohesins regulate the insulator function of CTCF and are regulated by cohesins.