University of Illinois researchers have adapted CRISPR gene-editing technology to cause the cell's internal machinery to skip over exons, a small portion of a gene, when transcribing it into a template for protein building. This gives researchers a way not only to eliminate a mutated gene sequence, but to influence how the gene is expressed and regulated.
CRISPR technologies typically turn off genes by breaking the DNA at the start of a targeted gene, inducing mutations when the DNA binds back together. This approach can cause problems, such as the DNA breaking in places other than the intended target and the broken DNA reattaching to different chromosomes. The new CRISPR-SKIP technique, described earlier this week in Genome Biology, does not break the DNA strands but instead alters a single point in the targeted DNA sequence.
"Given the problems with traditional gene editing by breaking the DNA, we have to find ways of optimizing tools to accomplish gene modification. This is a good one because we can regulate a gene without breaking genomic DNA," said Illinois bioengineering professor Pablo Perez-Pinera, who led the study with Illinois physics professor Jun Song.
CRISPR-SKIP alters a single base before the beginning of an exon, causing the cell to read it as a non-coding portion. "When the cell treats the exon as non-coding DNA, that exon is not included in mature RNA, effectively removing the corresponding amino acids from the protein," said Michael Gapinske, a bioengineering graduate student and first author of the paper.
While skipping exons results in proteins that are missing a few amino acids, the resulting truncated proteins often retain partial or full activity, which may be enough to restore function in some genetic diseases, said Perez-Pinera, who also is a professor in the Carle Illinois College of Medicine.
There are other approaches to skipping exons or eliminating amino acids, but since they don't permanently alter the DNA, they provide only a temporary benefit and require repeated administrations over the lifetime of the patient, the researchers said.
"By editing a single base in genomic DNA using CRISPR-SKIP, we can eliminate exons permanently and, therefore, achieve a long-lasting correction of the disease with a single treatment," said Alan Luu, a physics graduate student and co-first author of the study. "The process is also reversible if we would need to turn an exon back on."