Suppression of Transgene Silencing by Matrix Attachment Regions in Maize

Abstract

Matrix attachment regions (MARs) are DNA sequences that bind an internal nuclear network of nonhistone proteins called the nuclear matrix. Thus, they may define discrete gene-containing chromatin loops in vivo. We have studied the effects of flanking transgenes with MARs on transgene expression levels in maize callus and in transformed maize plants. Three MAR elements, two from maize ( Adh1 5 MAR and Mha1 5 MAR) and one from yeast (ARS1), had very different effects on transgene expression that bore no relation to their affinity for the nuclear matrix in vitro. In callus, two of the MAR elements ( Adh1 5 MAR and ARS1) reduced transgene silencing but had no effect on the variability of expression. In transgenic plants, Adh1 5 MAR had the effect of localizing ␤ -glucuronidase expression to lateral root initiation sites. A possible model accounting for the function of Adh1 5 MAR is discussed.

The Rb7 Matrix Attachment Region Increases the Likelihood and Magnitude of Transgene Expression in Tobacco Cells: A Flow Cytometric Study

“…However, it was not possible for Mankin and coworkers to determine if these increases in expression were due to greater proportions of expressing cells, cells expressing at higher levels, or both. Our data are in agreement with those of Brouwer et al (2002) and Mankin et al (2003), in that when MARs are incorporated into transgene constructs, we see an increase in the likelihood of expression. However, in contrast with Brouwer et al (2002), we observe that the expressing cells in lines transformed DNA was isolated from liquid cultures initiated from callus sectors ( Figure 6A, right column).…”

“…The authors noted fewer nonexpressing lines among lines that contained either the yeast (Saccharomyces cerevisiae) ARS1 MAR or the maize Adh1 59 MAR than among control lines. Based on these observations, they suggested that MARs increase the likelihood that an integrated gene will be expressed but not the level of expression (Brouwer et al, 2002). Mankin et al (2003) observed a similar MAR-induced reduction in the frequency of low expressing tobacco cell lines, but also noted that when these low expressing cell lines were removed from the analysis, MAR lines still showed an increase in GUS expression.…”

“…Because Brouwer et al (2002) used traditional methods of assessing transgene expression in their studies of the effect of MARs on LUC expression in maize (Zea mays) cells in culture, they were not able to assess epigenetic variation within a line. They did however examine variation across a large number of transgenic lines.…”

The Presence of a Chromatin Boundary Appears to Shield a Transgene in Tobacco from RNA Silencing

“…Current assays for boundary element efficacy and the potential protection against gene silencing require the comparison of different constructs at different integration sites in large populations of plants or cells. Therefore, boundary action may be confounded with parameters beyond experimental control, such as different spectra of integration sites, complex integrations, boundary-transgene interactions, and boundary-plant species interactions (Brouwer et al, 2002).…”

Mapping analysis of scaffold/matrix attachment regions (s/MARs) from two different mammalian cell lines

“…The site where this chromatin fibers bind to matrix protein is called S/MAR [8,10]. Interaction between S/MAR and matrix protein causes the formation of a distinct loop domain which localize gene transcription units and specific regulatory elements to regulate transcription [4,11].…”