Electric Frog Face
There are always oddities and strange patterns. For the first time, Tufts University biologists have reported that bioelectrical signals are necessary for normal head and facial formation in an organism and have captured that process in a time-lapse video that reveals never-before-seen patterns of visible bioelectrical signals outlining where eyes, nose, mouth, and other features will appear in an embryonic tadpole. The Tufts biologists found that, before the face of a tadpole develops, bioelectrical signals (ion flux) cause groups of cells to form patterns marked by different membrane voltage and pH levels. When stained with a reporter dye, hyperpolarized (negatively charged) areas shine brightly, while other areas appear darker, creating an electric face.
Bioelectricity) refers to the electrical, magnetic or electromagnetic fields produced by living cells, tissues or organisms. Examples include the cell membrane potential and the electric currents that flow in nerves and muscles, as a result of action potentials.
Frogs have often been in the forefront of bioelectricity. In the late eighteenth century, the Italian physician and physicist Luigi Galvani first recorded the phenomenon while dissecting a frog at a table where he had been conducting experiments with static electricity.
The new discovery was a case of scientific serendipity. Adams One of the authors) has spent years studying bioelectrical patterning and left-right developmental differences. Her frequent research tool is a camera hooked up to a microscope that sends images to a computer.
One evening in September 2009 Adams was making time-lapse movies of early stage tadpole development. The images were coming out particularly clearly—no small achievement when filming tiny living creatures. She decided to leave the camera on overnight even though she anticipated that as the developing embryos began to move, the images would likely become too blurred to be useful.
The imagery revealed three stages, or courses, of bioelectric activity.
First, a wave of hyperpolarization (negative ions) flashed across the entire embryo, coinciding with the emergence of cilia that enable the embryos to move. Next, patterns appeared that matched the imminent shape changes and gene expression domains of the developing face. Bright hyperpolarization marked the folding in of the surface, while both hyperpolarized and depolarized regions overlapped domains of head patterning genes. In the third course, localized regions of hyperpolarization formed, expanded and disappeared, but without disturbing the patterns created during the second stage. At the same time, the spherical embryo began to elongate.
The Tufts team found that disrupting bioelectric signaling by inhibiting ductin (a protein that is part of the machinery that transports hydrogen ions) correlated with craniofacial abnormalities.
Some embryos then grew two brains rather than one; others had thickened optic nerves or lacked normal nasal or jaw development. Interrupting the ion flux also altered the bioelectric patterns on the embryos' surface and expression of important face patterning mRNAs (messenger RNA that acts as a blueprint for proteins).
"Our research shows that the electrical state of a cell is fundamental to development. Bioelectrical signaling appears to regulate a sequence of events, not just one," said Laura Vandenberg. "Developmental biologists are used to thinking of sequences in which a gene produces a protein product that in turn ultimately leads to development of an eye or a mouth. But our work suggests that something else — a bioelectrical signal - is required before that can happen. "
"Studying bioelectrical signaling has led us to a different, and broader, way of thinking about diseases like cancer, birth defects and tissue regeneration," Adams notes. "Potentially we can find electrical switches that turn on entire developmental cascades rather than having to find many specific tools that turn on many specific genes within that cascade, as is the current approach with gene therapy. After all, we already have tools for regulating some of these bioelectrical signals, such as drugs that prevent acid reflux by controlling potassium and hydrogen ions."
For further information: http://www.physorg.com/news/2011-07-frog-time-lapse-video-reveals-never-before-seen.html