The Chicken Lysozyme 5′ Matrix Attachment Region Increases Transcription from a Heterologous Promoter in Heterologous Cells and Dampens Position Effects on the Expression of Transfected Genes

Abstract

Matrix attachment regions (MARs) are DNA elements that dissect the genome into topologically separated domains by binding to a chromosomal skeleton. This study explored the putative influence of the MAR located 5' of the chicken lysozyme gene on expression of heterologous genes in heterologous cell systems. Expression of a construct with the chloramphenicol acetyltransferase (CAT) indicator gene controlled by the herpes simplex virus thymidine kinase promoter (TC) and a construct in which the same transcriptional unit is flanked by chicken lysozyme 5' MARs (MTCM) was assayed after stable transfection into rat fibroblasts. Median CAT activity per copy number in MTCM transfectants was elevated approximately 10-fold relative to that in TC transfectants. Total variation in normalized CAT activity decreased from more than 100-fold among TC transfectants to nearly 6-fold among MTCM transfectants. The steady-state level of transcripts and the relative rate of transcription were increased in MTCM transfectants, as shown by S1 nuclease and run-on transcription assays, respectively. The chicken lysozyme 5' MAR thus can confer elevated, less position-dependent expression on a heterologous promoter in cells of a different species by increasing the density of transcribing RNA polymerase molecules. MAR-mediated transcriptional enhancement suggests that MARs are important for gene expression and not just for DNA packaging.

Specialized chromatin structure domain boundary elements flanking a Drosophila heat shock gene locus are under torsional strain in vivo

“…The scs/scs' elements have not been reported to exhibit the in vitro matrix or scaffold binding properties characteristic of A/T-rich sequences known as MARs or SARs, and thus they may represent a distinct (although possibly related) functional class of chromosomal DNA elements. Several MAR/SAR elements have been found at locations that could formally be considered as chromosomal domain boundaries by several criteria, including their coincidence with regions of highly decreased sensitivity to DNase I (Stratling et al, 1986;Levy-Wilson & Fortier, 1989) and their ability to confer copy number-dependent, position-independent expression to linked transgenes in both permanently transformed cells and transgenic animals (Stief et al, 1989;Bonifer et al, 1990; Phi-Van et al, 1990). On the other hand, unlike the scs/scs' elements or a functionally similar element characterized at the chicken /3-globin locus (Chung et al, 1993), at least some MAR/SAR elements are not genetically neutral since, while inactive in transient assays, they have displayed distinct enhancing activity on linked genes when assayed in permanently transformed cells (Stief et al, 1989;Klehr et al, 1992;Bode et al, 1992).…”

Gene expression within a chromatin domain: the role of core histone hyperacetylation

“…(2) It should shield a gene from the influences of chromosomal surroundings and should, hence, confer the property of position-independent (i.e., copy numberdependent) expression on transgenes. Available data suggest that at least some of the SAR elements have this property (Stief et al, 1989;Bonifer et al 1990; Phi-Van et al, 1990; J. Schlake and J. Bode, unpublished results).…”

MAR elements regulate the probability of epigenetic switching between active and inactive gene expression

“…14 For instance, DNA sequences called matrix attachment regions (SMARs or MARs), are thought to associate to a nuclear matrix consisting of gene transcription and mRNA processing proteins and to decrease expression variegation or silencing. 15,16 In addition, they have been used successfully to stabilize transgene expression in mammalian cells from both integrating or episomally replicating vectors. 17,18 However, how these genetic elements increase gene expression remains unclear.…”