MRC National Institute for Medical Research, London
Science for Health
Characterising the function of locus control regions
23 September 2010
Locus control regions (LCRs) are gene regulatory elements that confer tissue-specific and position-of-integration-independent expression to genes. This makes them useful tools for transgenesis, but including an LCR in a transgenic construct can result in unwanted effects on adjacent endogenous genes at the point of integration. LCRs are thought to act via the establishment of active chromatin hubs but this process has remained largely unstudied.
The human CD2 gene contains a T-cell-specific locus control region (hCD2-LCR) which displays a relatively compact composition compared with other LCRs. Previous studies on the hCD2-LCR have demonstrated that the LCR achieves the position-independent expression in T cells of transgenic mice regardless of its orientation relative to the linked promoters by overcoming heterochromatin-mediated position effect variegation.
Dimitris Kioussis (pictured) and his research group, in NIMR’s Division of Molecular Immunology, studied the influence of the LCR on the regulation of the CD8 gene locus. They produced two knock-in mouse lines with hCD2-LCR inserts targeted to two different locations within the mouse CD8 gene complex. In normal development expression of CD8 genes in CD4 lineage T-cells is silenced, but in the knock-in mice the CD8 gene locus is initially activated by the LCR in lineages (CD4+ cells) in which the CD8 genes are silenced. However, after several replication cycles the CD4+ cells suppress the LCR’s action and silence the CD8 locus.
The analysis of CD8/LCR knock-in mice revealed that the hCD2-LCR overcomes the normal developmental silencing of the CD8 gene complex in the majority of the cells of the CD4 lineage. CD8 expression in knock-in mice largely reflects the hCD2 gene regulation, when used as a transgene, but it seems that the presence of the LCR in the CD8 gene complex is continuously contested in those lineages in which CD8 genes are supposed to be shut down. As a result the influence of the inserted LCR, which exerts its effect on the promoter of the endogenous CD8 genes, seems to weaken as cells undergo multiple rounds of replication.
Effective gene transfer relies on the site of insertion of a gene. This work, by helping us to further characterize the hCD2-LCR element, may help us understand how regulatory elements interact with each other and help design more appropriate vectors for gene transfer protocols.
Dimitris Kioussis
Original article
Ursula Menzel, Eleni Ktistaki, Mauro Tolaini, Henrique Veiga-Fernandes, and Dimitris Kioussis (2010)
Replication allows inactivation of a knocked-in locus control region in inappropriate cell lineages
Proceedings of the National Academy of Sciences of the USA epub ahead of print. Pubmed abstract
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