title: Chromatin insulator elements: establishing barriers to set heterochromatin boundaries.
abstract: Epigenomic profiling has revealed that substantial portions of genomes in higher eukaryotes are organized into extensive domains of transcriptionally repressive chromatin. The boundaries of repressive chromatin domains can be fixed by DNA elements known as barrier insulators, to both shield neighboring gene expression and to maintain the integrity of chromosomal silencing. Here, we examine the current progress in identifying vertebrate barrier elements and their binding factors. We overview the design of the reporter assays used to define enhancer-blocking and barrier insulators. We look at the mechanisms vertebrate barrier proteins, such as USF1 and VEZF1, employ to counteract Polycomb- and heterochromatin-associated repression. We also undertake a critical analysis of whether CTCF could also act as a barrier protein. There is good evidence that barrier elements in vertebrates can form repressive chromatin domain boundaries. Future studies will determine whether barriers are frequently used to define repressive domain boundaries in vertebrates.
authors.affiliation: Institute of Cancer Sciences, College of Medical, Veterinary & Life Sciences, University of Glasgow, Glasgow, Scotland, UK.
authors.forename: Gráinne
authors.initials: G
authors.lastname: Barkess
authors.forename: Adam G
authors.initials: AG
authors.lastname: West
mesh_terms: D000818:Animals; D000076246:CCCTC-Binding Factor; D002843:Chromatin / Q000235:genetics / Q000378:metabolism*; D057890:Epigenomics; D006570:Heterochromatin / Q000235:genetics / Q000378:metabolism; D006657:Histones / Q000378:metabolism; D006801:Humans; D038101:Insulator Elements / Q000235:genetics*; D063146:Polycomb-Group Proteins; D012097:Repressor Proteins / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D051720:Upstream Stimulatory Factors / Q000235:genetics / Q000378:metabolism
chemical_list: D000076246:CCCTC-Binding Factor; C000619697:CTCF protein, human; D002843:Chromatin; D006570:Heterochromatin; D006657:Histones; D063146:Polycomb-Group Proteins; D012097:Repressor Proteins; D014157:Transcription Factors; D051720:Upstream Stimulatory Factors