Future Work

Ideally, our project would have been a successful proof of concept for light-based cell-to-cell signaling. Unfortunately, we were unable to create a sender cell which produced light with a great enough intensity to activate the receiver cell. Optimization of the light output is necessary for our system to prove useful. The Lux Biobrick was created by the Cambridge team for the 2010 iGEM Competition and emits light with the correct wavelength to activate our receiver cell. The light output from Lux-transformed bacteria might create the necessary intensity of light output for the sender cell. If successful, the Lux-based bacterial sender cell coupled with our mammalian receiver cell would be an example of inter-kingdom signaling. Inter-kingdom signaling would increase the possibilities of sender and receiver cells and create a better chance of creating a robust system. A light based inter-kingdom signaling system would enable researchers to reproduce the complex mechanism of inter-kingdom signaling that is responsible for infectious disease transmission and also important in ecology, plant biology, and food safety. Furthermore, researchers could create systems in which cells from different kingdoms that were never before able to communicate would be capable of signaling to each other and novel multi-cellular systems could be developed to solve medical and environmental problems. Due to time constraints, we were not able to go this direction.

Applications

Light-based cell-to-cell signaling has enormous applications in a wide span of research. Small molecule signaling fails when barriers in the body such as the gastrointestinal tract or the blood brain barrier are involved. A signaling system based on luminescence would be able to achieve signaling across barriers. The orthogonality of our light-based cell signaling system is crucial. The receiver cells would be specifically engineered to respond to blue light from the sender cell, making the system highly selective. Many cells have similar surface or membrane proteins that often result in off-target effects in other signaling mechanisms. Another advantage with our system is that light propagation is almost instantaneous, inevitably making the signaling faster than a small molecule signaling mechanism, which is limited by diffusion rates.

The field of optogenetics uses an external light source to stimulate an ion channel to cause depolarization and a triggering of action potentials in a population of neurons. This optogenetic method reconstitutes diseased cells by bypassing the upstage neural circuit and stimulating the downstage cells directly. If this process could be regulated by a different cell population, then the triggering would be within the body and no outside light application would be necessary. Our sender cell that has an output light signal intense enough to activate a light-induced ion channel such as Channelrhodopsin 2 would do just that. Receiver cells engineered to respond to the light from sender cells could be designed to perform any desired function. As an example, activated sender cells could signal to receiver cells to produce insulin, eliminating the requirement for diabetics to have an insulin pump or inject insulin using needles.

In conclusion, the fully optimized and characterized light-based cell signaling system that we envisioned for our project would prove extremely beneficial to both researchers and patients.