To achieve an intensified downstream signaling to enhance the detection sensitivity, we employed the CRISPR activation (CRISPRa) system to simultaneously increase the expression of the core components of olfactory receptor signaling via lentiviral transduction, including GNAL, RTP1 and RIC8B. At the endpoint, a cAMP-activated reporter gene (luciferase) is transfected to read out the signaling strength in response to specific and different range of odors.
As a proof-of-principle, we choose two odor compound/receptor pairs (β-citronellol/OR1A1 and bourgeonal/OR1D2) to construct the iSmeller odor sensors and evaluate their sensitivity and specificity.
We also designed multiple sgRNAs targeting three signal pathway core genes GNAL, RTP1 and RIC8B. When a specific odor molecule binds to the corresponding olfactory receptor, it will open the downstream cAMP pathway, resulting in a certain amount of cAMP at the end point, which can be used for the final signal detection.
