What is the Difference Between ZFN TALEN and CRISPR

The key difference between ZFN TALEN and CRISPR is that ZFN is a man-made gene editing technique based on Zinc finger nucleases composed of a zinc finger domain and a Fok1 endonuclease domain. Meanwhile, TALEN is a man-made gene editing technique based on fusion proteins composed of a bacterial TALE protein and Fok1 endonuclease, and CRISPR is a natural RNA based bacterial defence mechanism that is driven by two types of RNAs and associated Cas proteins.

Gene editing tools are based on the engineered nucleases comprised of sequence-specific binding domains and non-specific DNA cleavage modules. ZFN, TALEN, and CRISPR are three types of gene editing techniques. ZEN and TALEN are man-made systems, while CRISPR is a natural system occurring in bacteria. All three systems recognize sequences and cleave target DNA. Zinc finger nucleases are composed of a zinc finger domain and Fok1 endonuclease. TALENs are composed of a bacterial TALE protein and Fok1 endonuclease. CRISPR is composed of two RNAs (trans-activating crRNA and a single guide RNA).

CONTENTS

1. Overview and Key Difference
2. What is ZFN 
3. What is TALEN  
4. What is CRISPR
5. Similarities – ZFN TALEN and CRISPR
6. ZFN vs TALEN vs CRISPR in Tabular Form
7. Summary – ZFN vs TALEN vs CRISPR

What is ZFN?

ZFN is a gene editing tool based on zinc-finger nucleases. Zinc finger nucleases are chimeric nucleases composed of sequence-specific DNA-binding domains and non-specific DNA cleaving domains from the FokI restriction endonuclease. This is a man-made genome editing technology that enables a wide range of gene modifications by inducing double-strand breaks in DNA.

ZFN is an important tool when introducing targeted alterations in plants and several crop species. It allows the incorporation of valuable traits into plants. Moreover, ZFN has a therapeutic potential since it is able to perform precise genetic modification to eliminate the symptoms effectively.

What is TALEN?

Transcription activator-like nucleases (TALEN) is a gene editing tool that is based on chimeric nucleases similar to ZFN. It is also a man-made genome editing technology. TALEN induces gene modification by inducing double-strand breaks in DNA. TALENs are composed of sequence-specific DNA-binding domains fused to a non-specific DNA cleavage module. Therefore, it has FokI cleavage domains and DNA-binding domains derived from TALE proteins.

TALE proteins are naturally occurring in the bacterial genus Xanthomonas. These proteins contain DNA binding domains comprised of a series of 33-35 amino acid repeat domains. One of the major advantages of TALEN over ZFN is that the binding specificity of the DNA binding domain can be altered in TALEN by making modifications to 33-34 amino acid repeats.

What is CRISPR?

CRISPR stands for Clustered Regulatory Interspaced Short Palindromic Repeats. It is a natural RNA based defence mechanism executed in bacteria. In fact, it is a genome editing mechanism used especially against viruses. A virus or a foreign invader can activate this system in bacteria. CRISPR works together with the CRISPR-associated protein (Cas9).

CRISPR consists of two RNAs: trans-activating crRNA and a single guide RNA. Therefore, the recognition of CRISPR is dependent on both of these RNAs. When viral DNA enters a bacterial cell, the CRISPR locus produces guide RNA, which escorts Cas proteins to reach and bind with viral DNA and cleave at a specific location. Once viral DNA is cleaved, it becomes inactive due to the silencing of pathogenic DNA. Hence, the CRISPR system captures, cleaves and inactivates viruses with the help of Cas proteins.

CRISPR/Cas9 is used as a genome editing system. It is a recent technology. This technology is very simple, efficient, and cost-effective over other genome editing techniques. In comparison to ZFN and TALEN, CRISPR/Cas9 system is an efficient tool in inducing targeted genome alterations.

What are the Similarities Between ZFN TALEN and CRISPR?

• ZFN, TALEN, and CRISPR are gene editing techniques.
• All three tools will be promising techniques in correcting the genetic causes behind many diseases.
• However, they show constraints in targeting, imperfect specificity, and gene-targeting.
• All three systems can induce double-strand breaks.

What is the Difference Between ZFN TALEN and CRISPR?

ZFN is a gene editing technique based on Zinc finger nucleases while TALEN is a gene editing technique based on fusion proteins composed of a bacterial TALE protein and Fok1 endonuclease, and CRISPR is a natural RNA based bacterial defence mechanism that is driven by two types of RNA and associated Cas proteins. So, this is the key difference between ZFN TALEN and CRISPR.

The below infographic lists the differences between ZFN TALEN and CRISPR in tabular form for side by side comparison.

Summary – ZFN vs TALEN vs CRISPR

ZFN, TALEN, and CRISPR are gene editing technologies. CRISPR is the recent technology that shows better efficiency, feasibility, and multi-role clinical application. Both ZFN and TALEN are man-made artificial tools, while CRISPR is a bacteria defence mechanism. Both ZFN and TALEN are engineered nucleases. CRISPR consists of two RNA types associating with Cas proteins. Thus, this is the summary of the difference between ZFN TALEN and CRISPR.

Reference:

1. Gaj, Thomas, et al. “ZFN, Talen, and CRISPR/CAS-Based Methods for Genome Engineering.” Trends in Biotechnology, U.S. National Library of Medicine, July 2013.
2. Khan, Sikandar Hayat. “Genome-Editing Technologies: Concept, Pros, and Cons of Various Genome-Editing Techniques and Bioethical Concerns for Clinical Application.” Molecular Therapy – Nucleic Acids, Cell Press, 3 Apr. 2019.

Image Courtesy:

1. “Engineered Nucleases” By Farzad Jamshidi – Powerpoint  (CC BY-SA 3.0) via Commons Wikimedia
2. “Overview of TALENs” By Ogletreerd – Own work (CC BY-SA 4.0) via Commons Wikimedia
3. “Crispr” By James atmos – Own work (CC BY-SA 3.0) via Commons Wikimedia