MIT Researchers Use Light as a Remote Control Switch for CRISPR Gene Editing

September 6, 2016

Researchers at the Massachusetts Institute of Technology have engineered a remote control switch that uses ultraviolet (UV) light to activate CRISPR-Cas9 gene editing.

Researchers at the Massachusetts Institute of Technology have engineered a remote control switch that uses ultraviolet (UV) light to activate CRISPR-Cas9 gene editing. The tool, dubbed CRISPR-PLUS, allows closer study of gene expression and might eventually lead to therapeutic applications against melanoma and other cancers.

“The photoactivation capability of our CRISPR-PLUS method is compatible with the simultaneous targeting of multiple DNA sequences and supports numerous modifications that can enable guide RNA labeling for use in imaging and mechanistic investigations,” the coauthors wrote in a study

in Angewandte Chemie International Edition.

The team tested CRISPR-PLUS using a jellyfish gene for green fluorescent protein (GFP) and cancer-associated CD33 and CD71 genes.

The system “photo-cages” CRISPR-Cas9 so that genome editing is triggered only when UV light is delivered to target cells, the researchers explained. That should allow tighter control of the timing of gene edits and more precise views into the molecular details of tumor progression-which, in turn, could offer new insight into when gene-targeting therapies are best deployed to inhibit tumor progression or metastasis.

It might also lead to a new therapeutic modality in its own right-one that targets expression of cancer-driving genes. Ironically, CRISPR-PLUS might provide a way to turn UV light, a culprit in skin cancer tumorigenesis, against melanoma, by blocking the expression of tumor-driver genes.

“The advantage of adding switches of any kind is to give precise control over activation in space and time,” explained senior study author Sangeeta Bhatia, MD, PhD, of MIT’s Koch Institute for Integrative Cancer Research, in a news release.

Borrowed from the adaptive immune system of prokaryotes like bacteria, CRISPR-Cas9 allows researchers to deactivate or replace genes in living eukaryotic cells more simply and reliably than other genome-editing platforms.

CRISPR-Cas9 is composed of the Cas9 enzyme and a single chimeric guide-RNA (sgRNA) template that positions Cas9 at targeted genes, where it makes double-stranded DNA breaks. Most previous development of light-activated CRISPR gene editing has involved changes to the Cas9 enzyme, whereas CRISPR-PLUS altered the platform’s sgRNA component (hence the new technique’s name: CRISPR-Precise Light-mediated Unveiling of sgRNAs).

The sgRNA in CRISPR-PLUS binds to target genes only when exposed to UV light because of “protectors”- UV-breakable oligonucleotide sequences that temporarily bind to sgRNA and block its attachment to target genes.

“We designed protectors against different genes and showed that they all could be light-activated in this way,” Dr. Bhatia said.

The team hopes next to develop a “universal protector” that would circumvent the need to build new sgRNA-specific sequences for each targeted gene.