The realization that epigenetic control of gene expression can override regulatory information encoded in DNA provides the exciting opportunity to stably alter gene expression programs in vivo with the use of epigenetic modifiers. However, this aspiration is challenged by limitations in our ability to alter the epigenetic state of specific target genes in restricted cell types in a temporally regulated fashio. For this reason, we propose to combine novel genetic approaches that afford tight spatiotemporal control in vivo with innovative biochemical tools that allow the targeting of specific genomic loci in a sequence-specific manner. We will modify an assay that we previously designed for the inducible labeling of specific neuronal populations, named Tango, towards the controlled expression of synthetic TALE (Transcription Activator Like Effectors)-fusion proteins that will bind to target genomic loci and alter their epigenetic properties. As a model for these proof-of-principle experiments we will use the genetically, epigenetically and biochemically tractable mouse olfactory system. As we previously showed, the monogenic and monoallelic expression of olfactory receptor (OR) genes in olfactory sensory neurons (OSNs) is epigenetically regulated, both at the level of post-translational histone modifications and at the level of nuclear organization and distribution of active and silent OR alleles. Therefore, we propose to express TALE-fusion proteins with specificity for OR genes and their regulating enhancers in an inducible fashion in specific OSN subpopulations using variations of the TANGO system. This way we will alter the epigenetic state of active or silent ORs, and induce their re-positioning to distinct nuclear territories with the goal of stably altering their expresson pattern. This strategy of chemically or optically controlled epigenetic manipulations will be directly applicable to any other cell type in the mouse, and compatible with viral delivery methods that will make our approach applicable to future therapeutic interventions for human disease.
Epigenetic control of gene expression, through post-translational histone modifications or nuclear positioning, is crucial for proper development and function of the nervous system. Developing technologies for manipulating these epigenetic properties with high temporal and spatial precision will, therefore, be invaluable for the treatmen of various neurodevelopmental disorders.
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