Interdisciplinary Initiatives Program Round 5 – 2010

Michael Lin, Pediatrics
Mark Schnitzer, Applied Physics

The driving motivation behind our Bio-X funded research is our desire to understand how the brain thinks. To understand how the brain, a complex meshwork of integrated neuronal circuits, processes information, it will be important to record with high fidelity how electrical signals propagate through all of the many individual neurons that form a circuit.

To this end, we, the Lin and Schnitzer labs, are developing protein-based sensors that can be expressed by neurons and report on the occurrence of electrical impulses. Electrical impulses travel from one end of a neuron to the other in the form of propagating voltage changes at the plasma membranes, that is the cellular surfaces, of neurons. We are making sensors of electrical impulses by fusing fluorescent proteins, such as the famous green fluorescent protein of jellyfish, to a voltage sensing domain, a portion of a neuronal protein that resides in the plasma membrane and changes shape upon voltage change. These sensors emit light when a certain color of light is shone on them, with either the intensity or the color of emitted light changing with voltage changes. Supported by the Bio-X funding, the Lin and Schnitzer labs working together have succeeded in creating the highest dynamic range voltage sensors yet developed based on modulation of fluorescence resonance energy transfer, or FRET, between two fluorescent proteins attached to the voltage sensing domain. Voltage sensors that work by modulating FRET had been previously developed, but the degree of FRET change in response to single pulses of electrical activity was low, and the fluorescence output of the sensors dim. Together these factors made which allow reliable detection of action potentials in cultured neurons. We have created two new fluorescent proteins which when fused to a voltage sensing domain mediates an unprecedented degree of color change. These changes are large enough and the output bright enough that single pulses of electrical activity can be easily detected. We are now applying our expertise in fluorescent protein structure to develop reporters in which one color changes dramatically and quickly in intensity during an electrical impulse. This would make detection even more reliable and faster. We have preliminary evidence that a novel type of sensor design will be able to achieve this, and realizing this objective will be the goal of the next year.

Bio-X funding has been absolutely vital for this project. Bio-X funding incentivized the Lin and Schnitzer labs to tackle this technically challenging question together. It then provided the financial means to begin this project, which despite a solid conceptual foundation would have been deemed too risky for government grant support. The collaboration between our two labs has been incredibly productive, with five members between the two labs exchanging ideas, reagents, and results on a weekly basis. The rapid progress to date would have been impossible outside of this collaboration.