The discovery that the CRISPR gene editing process differs between human and algae cells could lead to improvements in the technique and boost production of useful products made from algae and plants. Image The development of CRISPR, a precision gene editing technology, revolutionised research by providing scientists with an easy way of finding and altering specific DNA sequences. Practical Applications The discovery that the process works differently in algae cells could be used to increase the yields of products currently made using algae, including some food supplements. Refinements to CRISPR could also be used to enable algae and plants to make new products such as renewable fuels, medicines, and other high value chemicals. The gene editing technique also has the potential to be used to engineer crops to increase yields, improve disease resistance or enable plants to thrive in harsh climates. Understanding DNA Repair Better understanding and improvements in CRISPR could not only unleash these and many other long discussed practical applications, but also provide new insights into how the genome works. However, there is a lack of understanding of one of CRISPR’s crucial steps, known as single-strand templated DNA repair (SSTR), which has mainly been studied in human and yeast cells. Not only does this limit improvements to precision editing process, but it could also mean that CRISPR may not work in the same way across other forms of life, such as plants or animals. To tackle this, researchers at the University of Edinburgh selected the widely used species of algae Chlamydomonas reinhardtii as a model to better understand the SSTR DNA repair process. During CRISPR ‘Cas’ proteins act as molecular scissors and are programmed to find, bind and cut almost any desired target sequence in DNA. Once the DNA is cut, the cell's natural repair mechanisms kick in to stitch the DNA back together. During this process edits can be made to the genome - adding new genes or modifying existing ones. Genetic Differences The results revealed that during the DNA repair process the behaviour of molecules which repair broken DNA strands, known as short single-stranded oligodeoxynucleotide (ssODN), differ between human and algae cells. In algae cells ssODNs physically incorporate into the genome to start the DNA repair process - this is known as the ‘bridge’ model. In contrast in human cells ssODNs act as a template for new DNA synthesis. Previous studies found that in human cells several components, known as the Fanconi anemia (FA) pathway, are involved in SSTR DNA repair. Yet this study revealed it was absent in algae cells. In contrast in algae cells an enzyme called polymerase θ controls the DNA repair process, yet this enzyme was not involved in human cells. Improving Gene Editing The findings highlight the genetic differences between humans and algae in SSTR DNA repair. This means that genome editing technologies may need to be tailor made for groups of animals or plants that share common ancestors, and potentially for each species of interest. Differences across species in, for example DNA repair pathways, could reveal new insights that could then be used to improve the gene editing process. The study, published in Nature Communications, was supported by UK Research and Innovation (UKRI), Biotechnology and Biological Sciences Research Council (BBSRC), PHYCONET and the Darwin Trust of Edinburgh. Related Links Mechanistic and genetic basis of single-strand templated repair at Cas12a-induced DNA breaks in Chlamydomonas reinhardtii, Nature Communications Attila Molnar Publication date 02 Mar, 2022
