Chemical Device Uses Light to Reprogram Gene Expression

Researchers at Texas A&M have developed a chemical or light-inducible transcriptional reprogramming device to illuminate the functions of genes during different biological processes, using calcium and light. The CaRROT system (calcium-responsive transcriptional reprogramming tool) can control the transcription of genes within the body with a high degree of precision, including how, when, and where genes create the proteins that perform various cellular functions.

The light-inducible device combines photoswitchable genetically encoded calcium actuators with dCas9 to control gene expression. (Cas9 is CRISPR-associated protein 9; dCas9, or dead Cas9, is a mutant form of Cas9).

The device uses light pulses to induce the flow of calcium ions into cells. The calcium signals generated by light are used to deliver the genome-engineering tool derived from the CRISPR/Cas9 system to turn on genes.

“When the light is switched on, the gates controlling calcium ions open to allow the flow of calcium from the external space into the cytoplasm of the cell,” said researcher Nhung Nguyen. “This process ultimately turns on the expression of specific genes.”

The turning on of gene expression can then lead to changes in the function of the cell.

“We have screened dozens of engineered proteins and undergone numerous rounds of optimization to make the CaRROT system strictly responsive to light,” said researcher Lian He.

To evaluate how effective CaRROT is in mammalian cells, the team will test it on genes that control the differentiation of neuron and skeletal muscle.

Researchers hope that CaRROT can be used in regenerative medicine as a tool to drive the precise differentiation of stem cells into any type of organ that is required.

“The improvement of light penetration in deep tissue makes us optimistic that we could use CaRROT to reprogram cells in damaged organs,” said researcher Yun Huang. “It is possible that one day, by just exposing the tissues to light, we can heal the wound or accelerate the regeneration of injured tissues by photo-tuning coordinated gene expression.”

CaRROT could also be used to document calcium-dependent activity in mammals after exposure to ligands or chemicals that would elicit calcium response inside cells.

The research was published in ACS Synthetic Biology (doi:10.1021/acssynbio.7b00467).