iGly: Novel tools for imaging glycine inhibitory neurotransmission

In the central nervous system (CNS), glutamate and glycine are pivotal excitatory and inhibitory neurotransmitters, respectively. Optical sensors for tracking neurotransmitters in space and time can provide important information on neurotransmission and signal processing. As an example, the development of the indicator iGluSnFR for the neurotransmitter glutamate, has led to ground-breaking advances in excitatory neurotransmission, particularly on synaptic spillover and exocytic vesicle fusion.

However, there is no equivalent biosensor to monitor glycine homeostasis and therefore information on inhibitory neurotransmission remains limited. Visualising glycine dynamics in vivo using fluorescent sensors would represent a significant new approach that will greatly contribute to understanding the processes mediated by this major neurotransmitter in health and disease.

In order to achieve this long-term goal, new glycine biosensors are urgently required. Considering the high demand for such biosensors, we propose an innovative project intended to fill this major experimental gap by developing a "toolbox" of entirely new genetically-encoded indicators that will allow in vitro, ex vivo and in vivo studies of inhibitory glycine neurotransmission.

Based on our track record in developing protein-based fluorescent sensors, we aim to create a unique palette of genetically-encoded glycine indicators optimised for in vivo imaging (iGly). iGly will subsequently allow direct, real-time, visualisation of glycine dynamics in tissues or living animals. A fluorescent indicator capable of real-time tracking of glycine concentration changes in vivo would be a breakthrough, since it could be tailored to reveal mechanisms of information processing, synaptic plasticity and neural circuits in the CNS.

This glycine monitoring "toolbox" will be made freely available (through repositories such as Addgene) to the scientific community as a resource and will help provide important new information as to the role of inhibitory neurotransmission in the CNS.