Abstract
The genomes of higher eukaryotes are partitioned into topologically associated domains or TADs, and insulators (also known as boundary elements) are the key elements responsible for their formation and maintenance. Insulators were first identified and extensively studied in Drosophila as well as mammalian genomes, and have also been described in yeast and plants. In addition, many insulator proteins are known in Drosophila, and some have been investigated in mammals. However, much less is known about this important class of non-coding DNA elements in plant genomes. In this review, we take a detailed look at known plant insulators across different species and provide an overview of potential determinants of plant insulator functions, including cis-elements and boundary proteins. We also discuss methods previously used in attempts to identify plant insulators, provide a perspective on their importance for research and biotechnology, and discuss areas of potential future research.
Highlights
Insulators, or boundary elements, are non-coding cis regulatory elements that are important for proper gene regulation and the maintenance of chromosome organization.Insulators have two major functions related to gene regulation: enhancer-blocking and barrier functions
Two key elements are necessary for the proper functioning of insulators: (1) the presence of certain DNA motifs, acting as binding sites for (2) specific proteins known as insulator, boundary, or architectural proteins
Reporter-based assays show that insulator activity (e.g., “boundary strength”—the ability of an insulator to effectively block interactions between loci located on either of its sides) is positively correlated with the occupancy level of architectural protein binding sites, suggesting co-binding by architectural proteins underlies the functional potential of these loci [17]
Summary
Insulators, or boundary elements, are non-coding cis regulatory elements that are important for proper gene regulation and the maintenance of chromosome organization. Insulators have two major functions related to gene regulation: enhancer-blocking (preventing unwanted enhancer–promoter interactions) and barrier functions (stopping the spread of repressive or active chromatin along the chromosome). These activities have been identified through transgene assays in model organisms. Insulators organize the chromosome into a series of discrete regions. Pairs of insulators interact with each other to generate chromosomal loops and form the basis of topologically associated domains (TADs). Two key elements are necessary for the proper functioning of insulators: (1) the presence of certain DNA motifs, acting as binding sites for (2) specific proteins known as insulator, boundary, or architectural proteins
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