Recently, Han Chunyu, an associate Professor of Hebei University of Science & Technology, with his research group members, published their latest research achievement---NgA-gDNA, a brand new genome editing technology, on famous British scientific journal---Nature Biotechnology. Some experts commented, although this technology is still in its infancy, its potential is expected to exceed the popular CRISPR-Cas9 technology in genetics and molecular biotechnology research field.
NgA-gDNA technology is a kind of genome editing technology, which uses DNA as the guiding tool. Its working principle is similar to that of CRISPR-Cas9 technology. That is leading the nuclease to cut gene sequences on specific sites under the help of oligonucleotides as guiding tools, and then carrying on genome editing. The main difference between NgA-gDNA and CRISPR-Cas9 system is that the guiding tool of NgA-gDNA system is a segment of guide DNA(dDNA) rather than gRNA in CRISPR-Cas9’s. Since proteins are no longer required to find target sequence, and compared with previous genome editing technologies, both NgA-gDNA and CRISPR-Cas9 technologies are much more simple and convenient to operate, which is definitely conducive to its promotion in applications.
Nuclease utilized in NgA-gDNA technology is NgAgo, an Ago endonuclease existing in natronobacterium gregoryi. Initially, Dutch scientists found Ago could cut genomic targets precisely and effectively. However, temperature (65-75°C) required for efficient Ago endonuclease was the main restriction at that time, because it can not be achieved under physiological conditions. While through the continuous efforts, Professor Han Chunyu and his research group members eventually found that homologous protein of Ago extracted from natronobacterium gregoryi has the similar function under physiological conditions.
Compared with CRISPR-Cas9 technology, NgA-gDNA has more advantages. For instance, NgAgo-DNA technology has a greater range of options in editable target sites. Cas9 needs 19 bases to match the expected genome loci and a protospacer-adjacent motif (PAM, a particular three-bases sequence), which limits the range of target sites options to a certain extent. Conversely, the selections of target sites are not restricted by PAM sequence in NgA-gDNA system, which allow this technology to edit nearly all loci of genome.
Moreover, the length of gDNA tandem with NgAgo is 24 bases, which are 5 bases longer than the gRNA with Cas9. And its accuracy will be improved by 1024 times theoretically. Furthermore, Han Chunyu team also found that NgAgo-gDNA has lower tolerance to guide–target mismatches, higher editing accuracy and more effective avoidance of off-target happening.
However, some scholars are still believing that CRISPR-Cas9 system are predominant in clinical trials. This technology uses well-transcribed sgRNA and purified Cas9 protein in vitro expression. Half-period of RNAs and proteins in vivo is very short, which can greatly reduce the treatment risks from exogenous substances. NgAgo-gDNA and CRISPR-Cas9 systems have their own advantages. Although the excellent discoveries by Professsor Han Chunyu’s team in the field of genome editing is superior and innovative, its practical applications and bio-security should be verified with more experimental data and trials.
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