A new gene editing method allows researchers to target many different kinds of disease-causing mutations in multiple cell types, which could have implications for genetic disorders such as Huntington’s disease, a study suggests.
The new method was described in the journal Cell Research in a study, titled “Precise in vivo genome editing via single homology arm donor mediated intron-targeting gene integration for genetic disease correction.“
“Gene editing” can refer to any technique that changes the DNA sequence of a living cell. Most current techniques — notably the CRISPR/Cas-9 technology — work well in cells that are actively dividing, but less so in non-dividing cells (such as brain nerve cells).
CRISPR/Cas-9 allows scientists to edit genomes with unprecedented precision, efficiency, and flexibility. The cas genes encode special enzymes that can cut or unwind DNA and are located near the CRISPR sequences. By delivering the Cas9 protein and appropriate ribonucleic acids into a cell, the organism’s genome can be cut at any desired location, like a tailor-made genetic modification.
The researchers behind the new report had previously developed a system based on CRISPR/Cas-9 called HITI (homology-independent targeted integration), which was effective in both dividing and non-dividing cells.
In the new study, they expanded on HITI and developed SATI (intercellular linearized Single homology Arm donor mediated intron-Targeting Integration), which allows for more types of mutations to be edited.
Most disease-causing mutations occur in parts of the genome that code for proteins — these coding parts account for about 2% of the total genome. Although the remaining non-coding parts have important functions (notably to help regulate the expression of different genes), targeting them — rather than the protein-coding genes themselves — may allow for more flexibility in gene-editing strategies.
Of note, gene expression is the process by which information in a gene is synthesized to create a working product, such as a protein.
“We sought to create a versatile tool to target these non-coding regions of the DNA, which would not affect the function of the gene, and enable the targeting of a broad range of mutations and cell types,” one of the study’s co-authors, Mako Yamamoto, PhD, a postdoctoral fellow at the Salk Institute, said in a news release.
“As a proof-of-concept, we focused on a mouse model of premature aging caused by a mutation that is difficult to repair using existing genome-editing tools,” she said.
The researchers specifically focused on a mouse model of progeria, a rare form of premature aging caused by a mutation in the LMNA gene. Using SATI, they inserted a non-mutated version of the LMNA gene into a nearby non-protein-coding region of DNA. Conceptually, this allows for the effects of the mutation to be lessened (because there is now a working version of the gene too), with fewer associated risks than there would be had the mutated gene been replaced.
Mouse models of progeria normally display signs of increased aging and have relatively short lifespans. Mice whose genomes were edited with SATI had significantly reduced signs of aging in organs such as the skin and spleen. Additionally, SATI-edited mice lived about 45% longer than non-edited mice with progeria, which translates to more than a decade for humans.
“This study has shown that SATI is a powerful tool for genome editing,” said Juan Carlos Izpisua Belmonte, PhD, a professor at the Salk Institute and senior author of the study.
“It could prove instrumental in developing effective strategies for target-gene replacement of many different types of mutations, and opens the door for using genome-editing tools to possibly cure a broad range of genetic diseases,” he said.
The team is now working on improving the efficiency of the SATI tool.
“Specifically, we will investigate the details of the cellular systems involved in DNA repair to refine the SATI technology even further for better DNA correction,” says Reyna Hernandez-Benitez, co-author of the study and a postdoctoral fellow at the Salk Institute.