IN SCIENCE

Gene editing tools enable scientists to study gene function and regulation more precisely, which could advance the field of biology and aid the understanding of diseases and developmental processes via generating cellular and animal models and functional genomic screens [2]. It could be used to recreate and study genetic changes for evolutionary studies, shedding light on how organisms have adapted and diversified over time.

IN MEDICINE

Gene editing produces one of the most tangible results in this field. It offers the possibility of correcting life-threatening genetic mutations that give rise to the various genetic disorders we see today. This can range from cystic fibrosis to sickle cell anaemia, and even muscular dystrophy [3]. Aside from genetic disorders, gene editing paves the way for novel therapeutics that include precise cancer therapies, immunotherapies, and personalised medicine.

IN AGRICULTURE, FOOD AND NUTRITION

Amidst the global food shortages caused by climate change, gene editing can be used to create crops that are more resistant to pests, diseases and environmental stresses like high temperatures [4]. It could also be used to enhance disease resistance in livestock, which increases animal welfare and reduces the need for antibiotics [5]. With hardier crops and livestock, both plant and animal agricultural productivity can be improved to address global food security challenges.

CAS NUCLEASES (CRISPR)

CRISPR utilizes a Cas9 nuclease to induce double stranded breaks (DSBs), which can be repaired via several cellular pathways to create a mix of insertion and deletion outcomes (indels). This process is not entirely specific as the formation of DSBs can cause large deletions and chromosomal translocations in the genome [6, 7]. It can also activate p53, possibly enriching oncogenic cells and increasing the risk of cancer [8].

BASE EDITING

Base editing allows for the creation of target point mutations without the need for DSBs [9]. It utilizes a Cas nuclease fused to a deaminase enzyme to chemically convert one base to another. However, its inability to introduce indels and transversions also hinder gene editing efforts. Its potential to similarly induce off-target mutations further limits its application in the real world [10].

PRIME EDITING

Prime editing utilizes a prime editor (PE), a fusion protein consisting of nCas9 (H840A) and an engineered Moloney Murine Leukemia Virus reverse transcriptase (MMLV-RT), and a prime editing guide RNA (pegRNA). It can also use a nicking guide RNA (ngRNA) to make it more precise. Unlike CRISPR, prime editing introduces single stranded nicks, which improves its precision and significantly reduces the possibility of off-target edits. It is also more versatile than base editing as it can introduce a wider variety of edits into the genome.

HOW PRIME EDITING WORKS

Figure 1.Graphical depiction of prime editing [11]

To initiate prime editing, the pegRNA binds to the DNA sequence of interest. The PE then creates a single-strand break in the DNA at the target site to allow MMLV-RT to access the DNA (Figure 1, Step 1). Subsequently, MMLV-RT synthesises a new DNA strand using pegRNA as a template (Figure 1, Steps 2-3). The information from the edited strand is thus copied to the complementary strand through the cell’s natural repair pathways (Figure 1, Steps 4-5).