Genetic engineering is known as a powerful technique for basic research and clinical applications. Recent progress in development of zinc-finger nucleases (ZFNs), which combine the DNA cleavage ability of Fok1 restriction enzyme with highly specific recognition properties of zinc-finger motifs, allows to improve efficiency and to broaden the field of use of genome editing. Here, we demonstrate our initial results in generating novel tools for Cathepsin D gene knockout in neurons based on ZFNs technology and mediated by adeno-associated virus (AAV) vectors. Pairs of AAV-ZFNs were produced and demonstrated the robust expression of nucleases in neuronal cell culture. Observed toxicity most likely was associated with heterodimerization but not homodimerization of ZFNs; cytotoxicity was greatly reduced when ZFN were provided at lower concentrations. Future studies evaluating efficiency of Ctsd knockout, off-target effects on molecular level and long-term outcomes in vivo can be performed.
Table of Contents
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
Molecular cloning
AAV production
Cell culture and transfection
Western blot
RESULTS
Construction of AAV vectors
ZFNs expression in neuronal cell culture
DISCUSSION
Research Objectives and Topics
The primary objective of this project is to develop and evaluate a novel gene-editing tool for the targeted knockout of the Cathepsin D (CTSD) gene in neurons using zinc-finger nucleases (ZFNs) delivered via adeno-associated virus (AAV) vectors.
- Design and construction of AAV-ZFN vectors with varying expression levels.
- Evaluation of ZFN-associated cytotoxicity in neuronal cell cultures.
- Analysis of ZFN expression and potential off-target effects.
- Optimization of AAV vector systems for efficient gene targeting in the central nervous system.
Excerpt from the Book
INTRODUCTION
Zinc finger nucleases (ZFNs) are engineered restriction enzymes which are employed as effective and versatile tools for targeted genome editing. Each ZFN consists of two functional domains: Fok1 restriction enzyme for DNA cleavage and zinc fingers (ZFs) for specific DNA binding (Figure 1). After heterodimerization of a ZFNs pair in an inverted orientation, Fok1 can induce double-strand breaks (DSBs) between the DNA sequences, specified by ZFs motifs. Assemblies of ZFs recognize DNA in a modular fashion, where a single ZF protein interacts with a single triplet of nucleotides, thereby allowing highly specific targeting of any DNA sequence in a complex genome (Palpant NJ, 2013). DSBs dramatically increase efficiency of gene targeting by stimulating two evolutionary conserved repair mechanisms. First is homologous recombination which underlies targeted gene replacement between existing sequence and designed donor DNA. Second, non-homologous end-joining, is a rapid but error-prone mode of DNA repair, which provides targeted mutagenesis by small insertions, deletions, substitutions etc (Caroll D, 2011).
ZFNs gene targeting was successfully applied in numerous model organisms including Drosophila melanogaster, Danio rerio, Caenorhabditis elegans, Xenopus, Arabidopsis, rodents etc (Palpant NJ, 2013) and various human cell lines and primary cells, such as T lymphocytes, mesenchymal stromal cells, embryonic stem cells, induced pluripotent stem cells etc (Händel EM, 2012). Gene editing frequencies up to 50% were reported (Lombardo A, 2007). But frequencies of desired gene modifications vary between different cell types and developmental stages, and depend on the method of ZFNs delivery (Caroll D, 2011), which stipulates a necessity to understand the biology and to assess an efficiency of gene targeting in every system under study.
Summary of Chapters
ABSTRACT: Provides a concise overview of the study, highlighting the development of AAV-delivered ZFN tools for CTSD knockout and the assessment of their toxicity in neuronal cultures.
INTRODUCTION: Introduces the biological mechanisms of ZFNs and their application in genome editing, contextualizing the need for CTSD-targeted gene therapy in neurodegenerative research.
MATERIALS AND METHODS: Describes the technical procedures for vector construction, AAV production, cell culture maintenance, and protein analysis via Western blot.
RESULTS: Presents the findings regarding vector design, ZFN expression levels in different cell types, and the observed correlation between ZFN concentration and cytotoxicity.
DISCUSSION: Interprets the experimental results, proposing strategies to mitigate ZFN-related toxicity and discussing the potential for future in vivo applications of this methodology.
Keywords
Zinc-finger nucleases, ZFNs, Cathepsin D, CTSD, Gene knockout, Adeno-associated virus, AAV, Genome editing, Neuronal culture, Cytotoxicity, Neurodegeneration, Molecular cloning, Genetic engineering, Off-target effects, DNA repair.
Frequently Asked Questions
What is the primary focus of this research?
The work focuses on the creation of a novel gene-editing tool designed to knockout the Cathepsin D gene in neurons using zinc-finger nucleases delivered via AAV vectors.
What are the key themes addressed in the study?
The study covers molecular cloning of ZFN constructs, AAV-mediated delivery systems, the evaluation of nuclease-induced toxicity, and the impact of different regulatory elements like WPRE on expression levels.
What is the main objective or research question?
The aim is to search for an optimal ZFN-pair configuration that achieves productive nuclease activity at the CTSD locus while minimizing toxic effects in neurons.
Which scientific methods are utilized?
The research employs molecular cloning, AAV production and purification, neuronal cell culture, co-transfection techniques, and Western blot analysis to verify protein expression.
What topics are covered in the main body?
The main body details the engineering of various AAV-ZFN vector versions, the experimental setups for transduction in HEK 293 cells and primary neurons, and the subsequent analysis of toxicity and protein accumulation.
Which keywords best characterize this work?
Key terms include Zinc-finger nucleases, CTSD, Gene knockout, Adeno-associated virus, and Neurodegeneration.
Why is Cathepsin D a target for this gene-editing project?
Deficiency in Cathepsin D is associated with NCL, a severe neurodegenerative disorder; therefore, developing tools to manipulate this gene is critical for understanding its role in protease pathways and protein aggregation.
What role does the WPRE regulatory element play in this study?
WPRE is used to enhance the expression of the AAV-delivered genes; however, the study finds that it also increases ZFN expression, which contributes to higher cytotoxicity in neuronal cultures.
What does the study suggest regarding the toxicity of ZFNs?
The study concludes that toxicity is likely linked to the heterodimerization of ZFNs at high concentrations and suggests that lowering the vector dosage can significantly reduce deleterious effects.
- Quote paper
- Maryna Psol (Author), 2013, Genetic knockout of Cathepsin D using zinc-finger nucleases delivered by AAV vectors, Munich, GRIN Verlag, https://www.grin.com/document/263385
