Endogenous Protein Tagging in Human Induced Pluripotent Stem Cells Using CRISPR/Cas9
August 25th, 2018
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Described here is a protocol for tagging endogenously expressed proteins with fluorescent tags in human induced pluripotent stem cells using CRISPR/Cas9. Putatively edited cells are enriched by fluorescence activated cell sorting and clonal cell lines are generated.
Overview
This protocol describes the tagging of endogenously expressed proteins with fluorescent tags in human induced pluripotent stem cells using CRISPR/Cas9. The method allows for the study of protein dynamics under endogenous regulatory control.
Key Study Components
Area of Science
- Stem Cell Biology
- Gene Editing
- Fluorescent Tagging
Background
- Endogenous tagging provides insights into protein localization and dynamics.
- Induced pluripotent stem cells (iPSCs) serve as a model for studying tagged proteins in non-transformed cells.
- The CRISPR-Cas9 system is utilized for precise genome editing.
- Fluorescent tags enable real-time observation of protein behavior.
Purpose of Study
- To generate iPSCs expressing endogenous fusion proteins with fluorescent tags.
- To enrich edited cells for further analysis.
- To explore the dynamics of proteins in various cellular contexts.
Methods Used
- CRISPR-Cas9 ribonucleoprotein complex delivery via electroporation.
- Fluorescence-activated cell sorting (FACS) for enriching edited cells.
- Clonal line generation for precise editing outcome analysis.
- Optimization of conditions for cell survival and editing efficiency.
Main Results
- Successful generation of over 35 different cell lines expressing tagged proteins.
- Knock-in efficiencies of up to 95% for targeted loci.
- Identification of monoallelic and biallelic edited clones.
- Ability to study protein dynamics in live cells.
Conclusions
- This method enhances the understanding of protein functions in live cells.
- It offers a versatile approach for studying various cellular processes.
- Potential for adaptation in other mammalian cell types.
Frequently Asked Questions
What is the main advantage of using CRISPR/Cas9 for tagging proteins?
CRISPR/Cas9 allows for precise genome editing, enabling the introduction of fluorescent tags directly into the genome, which maintains endogenous regulation.
How are the edited cells enriched after transfection?
Edited cells are enriched using fluorescence-activated cell sorting (FACS), which isolates cells expressing the fluorescent tags.
What types of cells can this protocol be adapted for?
While this study focuses on human induced pluripotent stem cells, the protocol could be optimized for other mammalian cell types.
What is the significance of using iPSCs in this study?
iPSCs provide a diploid, non-transformed model system that can differentiate into various cell types, allowing for diverse studies of protein dynamics.
What is the expected efficiency of the knock-in process?
Knock-in efficiencies can vary, typically ranging from 0.1% to 5%, with some loci achieving up to 95% efficiency.
How does the ROCK inhibitor contribute to the protocol?
The ROCK inhibitor promotes cell survival during electroporation and FACS enrichment, enhancing the overall success of the protocol.
Executive Industry Relevance
Endogenous protein tagging in hiPSCs using CRISPR/Cas9 enables precise, physiologically relevant studies of protein localization and dynamics in diploid, nontransformed human cells. This capability supports predictive confidence in early discovery and target validation by allowing direct observation of protein behavior under native regulatory control. The approach facilitates translational continuity across diverse isogenic cellular contexts, strengthening portfolio decision-making for cell-based therapeutic programs.
Strategic Applications in Biopharma R&D
Early Discovery & Target Validation
- Enables interrogation of protein function and localization in a native genomic context.
- Supports biological de-risking by avoiding artifacts from overexpression systems.
- Facilitates functional target validation through live-cell imaging of endogenously regulated proteins.
- Improves predictive confidence for downstream phenotypic screening and mechanistic studies.
Screening & Assay Development
- Generates validated hiPSC lines with fluorescently tagged proteins for reproducible assay development.
- Provides standardized, isogenic cellular systems for quantitative readouts in screening workflows.
- Enables scalable production of clonal lines for high-content imaging and compound evaluation.
- Supports robust assay standardization and platform reuse across discovery teams.
Translational & Preclinical Research
- Allows study of protein dynamics in differentiated cell types derived from hiPSCs, enhancing disease relevance.
- Maintains translational continuity from discovery through preclinical validation in isogenic systems.
- Enables alignment with translational biomarkers by tracking endogenous protein behavior in relevant cell types.
- Reduces risk of late-stage biological failure by ensuring mechanistic fidelity.
Pipeline & Workflow Integration
This method integrates into the discovery continuum from early target validation through assay development and preclinical research, supporting both mechanistic studies and translational applications.
- Discovery Biology: Provides direct hypothesis testing of protein function and localization in human cells.
- Screening: Delivers reproducible, quantitative fluorescent readouts for compound screening and phenotypic assays.
- Analytics: Enables precise measurement of protein expression, localization, and editing outcomes via FACS and microscopy.
- Translational Research: Supports continuity by enabling studies in differentiated, disease-relevant cell types from the same isogenic background.
- Enterprise Reuse: Establishes a reusable platform for generating and analyzing tagged protein lines across multiple targets and programs.
Operational & Enterprise Impact
- Scientific Value: Increases predictive confidence and reduces mechanistic ambiguity in target validation.
- Operational Value: Standardizes workflows for gene editing, enrichment, and clonal line generation in hiPSCs.
- Strategic Value: Enables better go/no-go decisions and capital efficiency by providing robust, physiologically relevant data early in the pipeline.
- Portfolio Impact: Supports risk-adjusted prioritization and advancement of targets with validated biological function.
Implementation Considerations
- Requires expertise in CRISPR/Cas9 editing, hiPSC culture, and FACS-based enrichment.
- Needs access to electroporation equipment, FACS instrumentation, and high-content imaging platforms.
- Demands rigorous cross-team standardization for editing, enrichment, and validation protocols.
- Adaptable to other mammalian cell types with protocol optimization for cell survival and editing efficiency.
- Genetic validation of clonal lines is essential to confirm precise editing and minimize off-target effects.
Biopharma FAQs
Why does null hypothesis testing matter for CRISPR-edited hiPSC target validation?
Null hypothesis testing ensures that observed protein localization and function changes in edited hiPSC lines are statistically significant and not due to random variation, supporting robust target validation decisions.
How does independent variable isolation fit the FACS enrichment workflow?
Isolating the variable of fluorescent tag expression via FACS allows teams to enrich for edited cells, ensuring downstream analyses reflect true editing outcomes rather than background or off-target effects.
What do quantitative dependent variable measurements enable in clonal line analysis?
Quantitative measurements of fluorescent intensity and localization in clonal lines enable precise assessment of editing efficiency and protein expression, informing selection of optimal lines for further study.
Why are replication requirements critical for cross-functional hiPSC editing projects?
Replication across multiple clonal lines and experiments ensures reproducibility and reliability of editing outcomes, facilitating collaboration and data confidence across discovery and translational teams.
What statistical analysis capabilities are required before implementing gene tagging in hiPSCs?
Teams must be able to analyze editing efficiency, allele distribution, and protein localization data statistically to confirm precise editing and support go/no-go decisions for downstream applications.
Chapters in this video
0:00
Title
2:29
Ribonucleoprotein (RNP) Transfection for CRISPR/Cas9 Mediated Knock-in in hiPSCs
5:15
FACS-enrichment of putatively edited hiPSCs
7:41
Generating putatively edited clonal hiPSC lines
10:36
Cryopreservation of clonal cell lines in 96-well plate format
12:21
Results
13:10
Conclusion
