IRES: Co-Expression of Transgenes and/or Generation of Reporter Models
The IRES (Internal Ribosome Entry Site) allows the researcher to co-express several genes under the control of the same promoter. Within the past decade, the IRES has been used to develop hundreds of genetically modified models, and is considered to be the ‘go-to’ technology for transgene co-expression in rodent animal models.
Applications of IRES technology.
1) Generation of multigenic-based disease models.
The IRES has been successfully used to generate models that mimic various human pathologies. Using an IRES, several cDNAs can be expressed under the control of the same promoter. This results in the co-expression of these genes in the same cells or tissues. The IRES has been successfully used to generate models of Alzheimer disease (see link).
Alzheimer Mouse Model: B. Platt et al. PlosOne 2011. Abnormal Cognition, Sleep, EEG and Brain Metabolism in a Novel Knock-In Alzheimer Mouse, PLB1.
2) Generation of reporter models.
The IRES can be utilized to insert a reporter gene at the 3’UTR of the gene of interest. Upon activation, the mRNA comprised of the construct IRES-reporter-target gene, is translated as two independent proteins. The reporter allows the researcher to quantify the gene expression level, to track the cells expressing the gene of interest and to monitor the regulation of the gene. Historically, such models have been generated, for example, to quantify the effector function of regulatory T cells, to quantify cytokine production, to follow cytokine-producing cells temporally, and to visualize a particular odorant receptor in olfactory neurons.
Regulatory T-cells: Y. Wan and A. Flavell. PNAS 2005. Identifying Foxp3-expressing suppressor T cells with a bicistronic reporter.
Olfactory neurons: C. Zheng. Neuron 2000. Peripheral olfactory projections are differentially affected in mice deficient in a cyclic nucleotide-gated channel subunit.
3) Generation of cell lineage tracking models.
IRES insertion at the 3' UTR of the gene of interest allows us to develop models for cell lineage tracking. Researchers may use these models to investigate and analyze the spatiotemporal cell fate of given cell populations.
Monitoring of cell progeny: Barker et al. Nature 2007. Identification of stem cells in small intestine and colon by marker gene Lgr5.
4) Monitoring cell expression patterns in KO models.
IRES systems are often used in KO models developed by high throughput KO consortia such as KOMP, EUCOMM and NorCOMM. These systems allow the researcher to monitor gene expression patterns and gene regulation in various tissues and cells.
5) Generation of models that allow for inducible ablation of a given cell type.
The IRES can be coupled to a suicide gene to selectively ablate a given cell population upon induction. The so-called “gene suicide” models can mimic degeneration of an organ or tissue (i.e. degenerescence) or help a researcher investigate the role of a given cell population in the homeostasis of target tissues. The cell ablation or gene suicide system can be inducible and reversible. This system has been used to develop models to study hepatitis.
6) Generation of tissue-specific Cre driver lines.
The IRES is often used for the generation of knock-in Cre driver lines. The knock-in approach allows the driver line to faithfully mirror the expression pattern of the selected Cre expression locus. The IRES sequence preserves expression of the target gene or allows the co-expression of a reporter gene. The reporter can provide information on expression level or on the expression pattern of Cre recombinase.
Cre driver lines: Taniguchi H. Neuron 2011. A resource of Cre driver lines for genetic targeting of GABAergic neurons in cerebral cortex.
How does it work?
The endogenous promoter of the target gene directs the transcription of a single mRNA containing coding regions for the gene of interest (see figure below, blue) and the fluorescent reporter gene (see figure below, red). The reporter and the gene of interest are expressed as two independent proteins (non-fused), which ultimately allows the reporter protein to remain fully functional. The endogenous expression of the gene of interest is preserved as much as possible.
Our licenses secure your discoveries and researches
The IRES technology is covered by a U.S. Patent (US6150169) owned by the University of Edinburgh.
genOway holds an exclusive license under the patent rights for the creation of genetically engineered mice.