Re-engineered optogenetic switches allow direct measurement of complex cellular systems

Dec 17, 2012

A Harvard University chemical biology lab has re-engineered optogenetic switches, photosensitive proteins called rhodopsins inserted into mammalian cells to control electrical firing, so that the switches run backward, firing off bursts of fluorescent light that reveal newly detailed patterns of electrical activity in neural networks, beating cardiac cells and developing embryos, according to a Dec. 17 presentation at the American Society for Cell Biology Annual Meeting in San Francisco.

Adam Cohen, PhD, said that optogenetic switches were pioneered in 2005 by Stanford University neuroscientist Karl Deisseroth, MD, Phd, in mammalian neurons, using light as a remote controller to turn them on or off. Rhodopsin switches have since allowed researchers to gain optical control over the electrical state and thereby the firing of neurons of worms, fish, mice and even monkeys.

In reversing the circuitry, Dr. Cohen has made the protein an indicator light, allowing his lab to directly measure electrical activity in complex cellular systems such as heart muscle. Researchers traditionally have inserted a very fine glass capillary into the cell and used a sensitive voltimeter to calculate voltage.

"This procedure is slow and laborious. We realized that could be conducted with much higher throughput, a possible boon for screens to identify neuronal or cardiac drugs," said Cohen, whose Harvard lab identified the rhodopsin protein Archaerhodopsin 3 (Arch), derived from the Dead Sea microorganism Halorubrum sodomense, as a fast and sensitive fluorescent indicator of membrane voltage.

Dr. Cohen and collaborators were able to express the Arch protein inside cultured rat neurons. Each time the rat neuron fired, the researchers saw and recorded a flash of fluorescence. With this technique, they created spatial maps charting the propagation of in neurons, providing a newly detailed look at how these impulses arise and spread. The researchers also expressed these voltage-indicating proteins in rat cardiac cells and monitored the electrical impulse associated with each heartbeat.

In human cardiac cells derived from human induced pluripotent stem cells (hiPSCs), Dr. Cohen and his team expressed Arch as a voltage indicator. Because these cells beat spontaneously in a culture dish, the researchers were able to plot the cells' responses to a wide variety of drugs by making optical measurements of the electrical activity of several thousand cells in a brief time period.

"Studies on hiPSC-derived are particularly exciting," said Dr. Cohen, "because they enable us to study cardiac electrophysiology in cells derived from people with genetic predispositions to a wide variety of cardiac diseases."

The Cohen lab has also expressed microbial rhodopsin proteins in living zebrafish. Because the fish are transparent, optical studies are possible without surgery. His lab has charted the electrical waves that initiate the heartbeat, the development in a zebrafish embryo of the heart from a quiescent patch of to a fully beating organ, and the firing of neurons in a zebrafish brain in response to external stimuli.

Arch is one of the over 5,000 known microbial rhodopsin proteins that generate colors. They share molecular kinship with the rhodopsin molecules in the human eye that enable color vision.

Explore further: The malaria pathogen's cellular skeleton under a super-microscope

More information: "Imaging voltage with microbial rhodopsins,"Monday, Dec. 17, 2012, 12:30-2 pm, Session: Voltage-gated Channels and Neurotransmission, presentation 1224 , poster B507, Exhibition Halls A-C

add to favorites email to friend print save as pdf

Related Stories

Researcher creates neurons that light up as they fire

Nov 29, 2011

In a scientific first that potentially could shed new light on how signals travel in the brain, how learning alters neural pathways, and might lead to speedier drug development, scientists at Harvard have created genetically-altered ...

New book explores stem cell therapies for heart disease

May 17, 2011

A new book edited by researchers at Worcester Polytechnic Institute (WPI) and the Stony Brook University School of Medicine provides a comprehensive look at the science and application of cellular therapies ...

Recommended for you

For resetting circadian rhythms, neural cooperation is key

19 hours ago

Fruit flies are pretty predictable when it comes to scheduling their days, with peaks of activity at dawn and dusk and rest times in between. Now, researchers reporting in the Cell Press journal Cell Reports on April 17th h ...

Rapid and accurate mRNA detection in plant tissues

20 hours ago

Gene expression is the process whereby the genetic information of DNA is used to manufacture functional products, such as proteins, which have numerous different functions in living organisms. Messenger RNA (mRNA) serves ...

For cells, internal stress leads to unique shapes

Apr 16, 2014

From far away, the top of a leaf looks like one seamless surface; however, up close, that smooth exterior is actually made up of a patchwork of cells in a variety of shapes and sizes. Interested in how these ...

User comments : 0

More news stories

Male monkey filmed caring for dying mate (w/ Video)

(Phys.org) —The incident was captured by Dr Bruna Bezerra and colleagues in the Atlantic Forest in the Northeast of Brazil.  Dr Bezerra is a Research Associate at the University of Bristol and a Professor ...

Scientists tether lionfish to Cayman reefs

Research done by U.S. scientists in the Cayman Islands suggests that native predators can be trained to gobble up invasive lionfish that colonize regional reefs and voraciously prey on juvenile marine creatures.

'Exotic' material is like a switch when super thin

(Phys.org) —Ever-shrinking electronic devices could get down to atomic dimensions with the help of transition metal oxides, a class of materials that seems to have it all: superconductivity, magnetoresistance ...