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Methods Mol Biol ; 2351: 307-320, 2021.
Artigo em Inglês | MEDLINE | ID: mdl-34382197


The transition from silenced heterochromatin to a biologically active state and vice versa is a fundamental part of the implementation of cell type-specific gene expression programs. To reveal structure-function relationships and dissect the underlying mechanisms, experiments that ectopically induce transcription are highly informative. In particular, the approach to perturb chromatin states by recruiting fusions of the catalytically inactive dCas9 protein in a sequence-specific manner to a locus of interest has been used in numerous applications. Here, we describe how this approach can be applied to activate pericentric heterochromatin (PCH) in mouse cells as a prototypic silenced state by providing protocols for the following workflow: (a) Recruitment of dCas9 fusion constructs with the strong transcriptional activator VPR to PCH. (b) Analysis of the resulting changes in chromatin compaction, epigenetic marks, and active transcription by fluorescence microscopy-based readouts. (c) Automated analysis of the resulting images with a set of scripts in the R programming language. Furthermore, we discuss how parameters for chromatin decondensation and active transcription are extracted from these experiments and can be combined with other readouts to gain insights into PCH activation.

Proteína 9 Associada à CRISPR/metabolismo , Regulação da Expressão Gênica , Heterocromatina/genética , Ativação Transcricional , Animais , Proteína 9 Associada à CRISPR/genética , Cromatina/genética , Cromatina/metabolismo , Fibroblastos/metabolismo , Imunofluorescência/métodos , Expressão Gênica , Heterocromatina/metabolismo , Processamento de Imagem Assistida por Computador , Camundongos , Microscopia de Fluorescência , Ligação Proteica , Transfecção , Fluxo de Trabalho
Methods Mol Biol ; 2173: 171-188, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32651918


Blue light-induced chromatin recruitment (BLInCR) is a versatile optogenetic tool to enrich effector proteins at specific loci within the nucleus using illumination in the 400-500 nm range. The resulting chromatin binding reaction is reversible on the time scale of minutes. BLInCR is advantageous over ligand-binding induced methods since it does not require a change of growth medium for the relatively slow depletion of the inducer from the nucleus. However, applying BLInCR for reversibility experiments is challenging because of the need to spectrally separate light-induced activation from visualization of the chromatin locus and effector and/or reader proteins by light microscopy. Here, we describe an improved BLInCR protocol for light-dependent association and dissociation of effectors using the near-infrared fluorescent protein iRFP713. Due to its spectral properties, iRFP713 can be detected separately from the red fluorescent protein mCherry. Thus, it becomes possible to trace two proteins labeled with iRFP713 and mCherry independently of the light activation reaction. This approach largely facilitates applications of the BLInCR system for experiments that test the reversibility, persistence, and memory of chromatin states.

Cromatina/metabolismo , Luz , Optogenética/métodos , Humanos , Software , Ativação Transcricional/genética , Ativação Transcricional/fisiologia
Methods Mol Biol ; 2038: 251-270, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31407290


Gene expression can be monitored in living cells via the binding of fluorescently tagged proteins to RNA repeats engineered into a reporter transcript. This approach makes it possible to trace temporal changes of RNA production in real time in living cells to dissect transcription regulation. For a mechanistic analysis of the underlying activation process, it is essential to induce gene expression with high accuracy. Here, we describe how this can be accomplished with an optogenetic approach termed blue light-induced chromatin recruitment (BLInCR). It employs the recruitment of an activator protein to a target promoter via the interaction between the PHR and CIBN plant protein domains. This process occurs within seconds after setting the light trigger and is reversible. Protocols for continuous activation as well as pulsed activation and reactivation with imaging either by laser scanning confocal microscopy or automated widefield microscopy are provided. For the semiautomated quantification of the resulting image series, an approach has been implemented in a set of scripts in the R programming language. Thus, the complete workflow of the BLInCR method is described for mechanistic studies of the transcription activation process as well as the persistence and memory of the activated state.

Luz , Microscopia Confocal , Microscopia de Fluorescência , Optogenética , Fatores de Transcrição/metabolismo , Transcrição Genética/efeitos da radiação , Ativação Transcricional/efeitos da radiação , Linhagem Celular Tumoral , Genes Reporter , Humanos , Fatores de Tempo , Fatores de Transcrição/genética
J Cell Sci ; 130(24): 4213-4224, 2017 Dec 15.
Artigo em Inglês | MEDLINE | ID: mdl-29122982


Gene expression is tightly regulated in space and time. To dissect this process with high temporal resolution, we introduce an optogenetic tool termed blue light-induced chromatin recruitment (BLInCR) that combines rapid and reversible light-dependent recruitment of effector proteins with a real-time readout for transcription. We used BLInCR to control the activity of a cluster of reporter genes in the human osteosarcoma cell line U2OS by reversibly recruiting the viral transactivator VP16. RNA production was detectable ∼2 min after VP16 recruitment and readily decreased when VP16 dissociated from the cluster in the absence of light. Quantitative assessment of the activation process revealed biphasic activation kinetics with a pronounced early phase in cells treated with the histone deacetylase inhibitor SAHA. Comparison with kinetic models of transcription activation suggests that the gene cluster undergoes a maturation process when activated. We anticipate that BLInCR will facilitate the study of transcription dynamics in living cells.This article has an associated First Person interview with the first author of the paper.

Cromatina/genética , Proteína Vmw65 do Vírus do Herpes Simples/genética , Transcrição Genética , Ativação Transcricional/genética , Linhagem Celular Tumoral , Cromatina/efeitos da radiação , Regulação da Expressão Gênica no Desenvolvimento/efeitos da radiação , Genes Reporter/genética , Humanos , Cinética , Luz