Sustained Transgene Expression Using MAR Elements

Abstract

Matrix attachment regions (MARs) are DNA sequences that may be involved in anchoring DNA/chromatin to the nuclear matrix and they have been described in both mammalian and plant species. MARs possess a number of features that facilitate the opening and maintenance of euchromatin. When incorporated into viral or non-viral vectors MARs can increase transgene expression and limit position-effects. They have been used extensively to improve transgene expression and recombinant protein production and promising studies on the potential use of MAR elements for mammalian gene therapy have appeared. These illustrate how MARs may be used to mediate sustained or higher levels of expression of therapeutic genes and/or to reduce the viral vector multiplicity of infection required to achieve consistent expression. More recently, the discovery of potent MAR elements and the development of improved vectors for transgene delivery, notably non-viral episomal vectors, has strengthened interest in their use to mediate expression of therapeutic transgenes. This article will describe the progress made in this field, and it will discuss future directions and issues to be addressed.

An S/MAR-based L1 retrotransposition cassette mediates sustained levels of insertional mutagenesis without suffering from epigenetic silencing of DNA methylation

“…18 The S/MAR element specifically interacts with the nuclear matrix, chromosome scaffold factors and other cellular factors, and is known for its long-term mitotic stability, resistance to gene silencing and cosegregation with host chromosomes upon cell division. 19,20 These unique properties of S/MAR prompted us to explore its ability to facilitate L1 retrotransposition and compare its expression profile with that of a currently used EBNA1-based vector in cultured human cells. Here we report that simple inclusion of the S/MAR in the vector backbone improved the levels of L1 expression and prolonged retrotransposition activity in human cells without any transcriptional silencing or dilution of vector, even in the absence of selective antibiotics.…”

Programming DNA replication origins and chromosome organization

“…MARs, together with DNA replication origin sequences, allow propagation of plasmid DNA without the use of selection agents (Jenke et al 2004). In addition, MARs enhance stable transgene expression, possibly through their chromatin-organizing activity (Harraghy et al 2008).…”

Use of human MAR elements to improve retroviral vector production

“…29,35,41,42 MAR elements have been previously shown to increase the stability and the expression of recombinant proteins from plasmids and viral vectors. 43,44 We recently identified and characterized potent human MARs that increase and sustain elevated protein expression over prolonged cell culture time as a consequence of decreased variegation and silencing. 45,46 In this study, we evaluated the performance of several human MAR elements to improve the viral production of SIN vectors.…”