Site-independent expression of the chicken beta A-globin gene in transgenic mice.
ABSTRACT The level of expression of exogenous genes carried by transgenic mice typically varies from mouse to mouse and can be quite low. This behaviour is attributed to the influence of the mouse chromatin near the site of transgene integration. This 'position effect' has been seen in transgenic mice carrying the human beta-globin gene. It was however, abolished when DNase I hypersensitive sites (normally found 65 to 44 kilobases (kb) upstream) were linked to the human beta-globin transgene. Thus, the upstream DNA (previously named a dominant control or locus activation region, now denoted a locus control region) conferred the ability to express human beta-globin at high levels dependent on copy number on every mouse carrying the construct. We report here an investigation of chicken beta A-globin gene expression in transgenic mice. A 4.5-kb fragment carrying the beta A-globin gene and its downstream enhancer, without any far upstream elements, is sufficient to ensure that every transgenic mouse expresses chicken globin messenger RNA at levels proportional to the transgene copy number. Thus the chicken DNA elements that allow position-independent expression can function in mice. In marked contrast to the human beta cluster, these elements are no farther than 2 kb from the gene. The location of the elements within the cluster demonstrates that position independence can be mediated by DNA that does not define a gene cluster boundary.
SourceAvailable from: Sergey V Razin[Show abstract] [Hide abstract]
ABSTRACT: Insulators were first identified as genomic elements either blocking communication between promoters and en-hancers (enhancer-blocking activity) or restricting heterochromatin spreading (barrier activity). There are seve-ral types of insulators in Drosophila which utilize different proteins. All insulators identified in vertebrates work with the help of the multifunctional transcription factor CTCF. Biological functions of vertebrate insulators are not clear yet. They are supposed to separate chromatin domains albeit there is almost none direct evidence of this fact. The most significant is the participation of insulators in maintenance of centers of imprinting (im-printing choice regions). The results of a number of recently published articles indicate that isolation of a gene by placement of this gene into a separate topological domain (loop) is crucial to establishing imprinting. In this particular case as well as in many other cases insulators serve as architectural elements supporting the three-dimensional structure of genome. Moreover, interaction between pairs of insulators where cohesin plays a pivo-tal role along with CTCF folds genome into various loops.Biopolymers and Cell 07/2012; 28(4):252-260. DOI:10.7124/bc.000057
[Show abstract] [Hide abstract]
ABSTRACT: In the last quarter of the 20th century, studies with a number of model systems produced a hypothesis that the higher eukaryotic genome consists of functionally isolated areas termed genomic domains. Each domain includes one or more genes and a regulatory system that is normally active only for the given domain and allows it to achieve a regulatory autonomy of the neighboring chromosome regions. A genome domain is characterized by spectra of covalent histone modifications, which determine the domain boundaries and the extent of chromatin condensation within the domain, thus determining whether transcriptional activation is possible for the domain genes. The domain hypothesis of genome organization is due, to a large extent, to studies of the mechanisms regulating transcription of the globin genes in vertebrates. The chicken β-globin gene domain is one of the most popular models in the field. The model was used to investigate the basic principles of the complex function of higher eukaryotic enhancers, the properties of insulators and functional units of eukaryotic enhancers and promoters, the influence of covalent histone modifications on the extent of chromatin condensation, and the role of such modifications in regulating transcription within the domain. The review summarizes the data on the chicken β-globin gene domain and considers the domain hypothesis of eukaryotic genome organization.Molecular Biology 09/2012; 46(5). DOI:10.1134/S0026893312040127 · 0.74 Impact Factor
[Show abstract] [Hide abstract]
ABSTRACT: Despite progress in understanding genome organization and gene expression during the last decade, the evolutionary pathways that led to the intricate patterns of gene expression in different cells of an organism are still poorly understood. Important steps in this regulation take place at the level of chromatin, where the (epi)genomic environment of a gene determines its expression in time and space. Although the basic mechanisms of gene expression apply to all eukaryotes, multicellular organisms face the additional challenge of coordinating gene expression during development. In this review we summarize and put into evolutionary context current knowledge about chromatin insulators, an important class of regulatory factors mediating these tasks. Our interpretation of historical and recent findings points to a dynamic and ongoing evolution of insulator proteins characterized by multiple instances of convergent evolution, gene loss, and binding site changes in different organisms. The idea of two autonomously evolving insulator functions (as a barrier element and an enhancer blocker) further suggests that the evolution of metazoans and their enhancer-rich gene regulatory repertoire might be connected to the radiation of enhancer blocking insulators. Although speculative at the moment, such coevolution might create tools for complex gene regulation and therefore influence the evolutionary roadmaps of metazoans.Trends in Genetics 04/2014; DOI:10.1016/j.tig.2014.03.004 · 11.60 Impact Factor