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signature voltage drop. Wherever the
researchers triggered the electrical signal, eyes grew.
“What this says is there’s lots of ways
to get to that membrane potential, and it
doesn’t matter how you get there,” says
Angie Ribera, a developmental neuro-biologist at the University of Colorado
Denver Anschutz Medical Campus in
Aurora. She is interested in learning
which channels normally cause the electrical signature and what regulates them.
Researchers previously thought that
only certain cells in the head could make
eyes, because inserting proteins such
as the master eye regulator Pax6 into
cells could cause eye growth only in the
head. But the electrical signal can trigger eye development almost anywhere,
indicating that the membrane potential
somehow supersedes molecular information for telling a cell what to do.
Although the electrical signal is important for initiating eye formation, it does
require proteins previously identified as
important regulators of eye development.
Somehow, dropping the cells’ membrane
potential to the narrow window of voltage
that triggers eye formation also turns on
Pax6, which activates genes involved in
making eyes. Without Pax6 the tadpoles
are unable to grow eyes.
Lens tissue (shown in red) can be detected growing in both the eye and the tail of this tadpole. Researchers showed that they could cause eyes to grow anywhere on a frog’s body by manipulating cells’ electric potential.
Changing the electrical properties
of cells could be a much easier way to
promote regeneration than altering
the ways proteins work, says Panagiotis
Tsonis, a developmental molecular biol-
ogist at the University of Dayton in Ohio.
“It is very intriguing and very interest-
ing, but of course, the mechanism is not
While Levin’s group has had success
regrowing a tadpole’s tail and creating
eyes where none should be in animals,
Tsonis doubts electrical manipulation
will work as well for coaxing stem cells
in lab dishes to grow into specific organs.
Development may depend upon a cell’s
electrical status relative to surrounding
cells, not just on reaching a particular
Levin’s group is working to fill in the
details about how the membrane potential is generated and how it leads to eye
development. He also wants to determine whether other organs have particular electrical signatures.
Biological electricity has mostly been
ignored except by scientists studying nerves and muscles, but now more
researchers may consider how electrical
properties affect development.
“The thing about this that is so cool is
that the eye is thought of as the epitome
of a complex structure,” Coffman says.
“The fact that a narrow range of voltage is enough to specify an eye is kind of
michael Levin’s group is just about the only one currently
investigating how bioelectricity influences development, but
the field has a long history. scientists discovered as early as
1941 that severed amphibian limbs produce current as they
regenerate. that fact was rediscovered in 1977 by richard
borgens of purdue University and colleagues, who measured
electrical currents flowing in the severed limbs of newts.
Levin’s group has taken the observation to a new level and
has shown that manipulating electrical properties of cells
can produce strange results, such as this four-headed planarian worm. the team reported in the Jan. 28 Cell Chemistry
and Biology that particular membrane voltages are needed
to regrow severed heads on the famously regenerative flatworms, which can develop into two whole individuals after
being cut in half.