YSM Issue 86.4

School of Medicine Professors Illuminate
the Language of the Brain
BY WILLIAM GE
Dr. Vincent Pieribone, Associate Professor of Neurobiology at Yale
School of Medicine, is currently submarine diving in the Solomon
Islands in search of shining proteins. If he finds them, it will mean
advancement for the entire field of neurology.
Understanding how
the brain works is
undeniably one of the
greatest challenges of
our time, and one that
dates back hundreds
of years. Although
scattered hypotheses
have long strained
for a coherent theory
of the brain, efforts
have been limited
by our ignorance
of the brain’s
labyrinthine circuitry.
“Traditionally, we
would rely on invasive
electrodes to sample
very limited areas of the brain, and only a few
neurons at a time,” Pieribone explained. A 2012
study at the University of California, Berkeley
characterized this level of imaging as akin to
viewing “an HDTV program by looking just
at one or a few pixels on a screen.” Imaging
technologies such as fMRI have improved our
historical myopia of the brain’s inner circuits, but
they are indirect methods which monitor areas
of high metabolism in the brain, as opposed to
actual neurons firing.
A collaboration between Dr. Vincent Pieribone and Dr. Michael
Nitabach of the Yale School of Medicine has produced a chimeric,
engineered molecule which has the power to illuminate the circuitry
of the brain. The molecule, dubbed ArcLight, has two functional
components. The first is a voltage sensor domain, a transmembrane
protein module containing positively charged amino acids. Voltage
changes across the membrane (in the case of neurons firing) cause a
change in the electric field in which these positive charges sit, and that
imposes a force on the positive charges and changes the conformation
of the domain. The second component, a mutated form of green
fluorescent protein (GFP), is fused to the voltage sensor domain. When
the sensor domain changes conformation, it also changes the shape
of the GFP, which affects the level of fluorescence. Thus, ArcLight
can be used to effectively map millions of neurons firing in real time
by the intensity of fluorescence each gives off.
The implications of this discovery are striking. “Behaviors and
biological processes can be associated with patterns of light,” explained
Pieribone. “For example, when people touch something, there is a
pattern associated with that action. We can ask: what does the brain
NEUROSCIENCE
do? Or, to add a twist, what happens if you lose your arms?” In their
study, Nitabach and Pieribone used ArcLight to demonstrate that
neurons involved in the circadian rhythm of a fruit fly were more
active in the morning than the evening. “This is something you could
only see this way,” said
Nitabach.
However, even this
new method of neural
imaging is not without
limitations. Current
efforts to improve the
protein probe include
increasing the intensity
of the fluorescent
signal in response
to smaller voltages
and increasing the
speed of response
(current lag time is
~20 milliseconds).
Moreover, the GFP
is limited to absorbing
blue light and emitting green light; if alternate
versions could be discovered that can absorb green
light (and thus emit red light), ArcLight could
be used in conjunction with other fluorescent
sensors (e.g. calcium detectors) which emit green
light to produce a system to investigate other
variables of brain activity. Finding these alternate
versions is one of the reasons why Pieribone is
diving in the deep Pacific. If the new proteins
are found, neural systems in which specific
processes can be excited by light (optogenetics)
Above: The mutant isolated from a fluorescent chordate, C. intestinalis (left), was
engineered into a molecule that can read a fruit fly’s (right) mind. Below: The lead
collaborators of the project, Vincent Pieribone (left) and Michael Nitabach (right).
IMAGES COURTESY OF YALE SCHOOL OF MEDICINE
IMAGES COURTESY OF ERIC GIBGUS/NUZRATH NUZREE
can be used concomitantly with ArcLight in order to selectively and
comprehensively decode the electrical circuits that lie at the heart of
neuroscience.
Last April, the Obama administration
unfurled a long-term scientific
effort to map the human
brain and its activity in the
Brain Research through
Advancing Innovative
Neurotechnologies
(BRAIN) Initiative. The
initiative is projected to
cost 300 million dollars
per year over a period
of the next ten years.
Here at Yale, in the
labs of Nitabach and
Pieribone, it looks like
it is already paying off.
IMAGE COURTESY OF
PROTEIN DATA BANK
A mutated form of the protein GFP
acts in ArcLight as the fluorescent
indicator of electrical activity.
www.yalescientific.org November 2013 | Yale Scientific Magazine 9