Left-right wiring determined by neural communication in the embryonic worm

May 17, 2007
Left-right wiring determined by neural communication in the embryonic worm
The AWC neuron on the worm's left side (red) and the AWC neuron on its right (yellow) reflect a ”handedness” that develops randomly in the C. elegans brain. This pattern is created by an unexpected network of gap junction channels in the worm embryo. Credit: Rockefeller University

Most animals appear symmetrical at first glance, but we're full of internal lop-sidedness. From the hand used to pick up a pencil or throw a baseball, to where language is generated in the brain, to the orientation of our internal organs, humans are a glut of asymmetries. Worms aren't so different: The roundworm Caenorhabditis elegans has nerves on its left and right sides that perform different functions. Like handedness, the determination of which nerves develop on which side seems random from worm to worm.

But now, Rockefeller University and Howard Hughes Medical Institute scientists working to demystify the worm's asymmetry have discovered that the arbitrary left-right configurations of two types of olfactory neurons are established during development. In a study released in the May 18 issue of Cell, the researchers show that embryonic worms have a system of gap junctions -- "broadband" communication channels through which cells pass many kinds of molecules and electrical signals -- that allow growing neurons on the left and right to communicate with each other, a system that dissolves as the worm develops.

Every neuron in the adult C. elegans has been mapped and named. Handedness researchers are particularly interested in two olfactory neurons, AWCON and AWCOFF, one each on the left and right side of the worm's body. AWCON has one set of responsibilities, while AWCOFF has a totally different set of functions. Which side houses each of the nerves -- right or left -- appears to be random, with their positions reversed about 50 percent of the time. "What makes this an interesting puzzle to solve is understanding how the left and the right side become different from each other, and how they coordinate their activity so that every worm still has exactly one of each type of cell," says the paper's senior author Cori Bargmann, Torsten N. Wiesel Professor and head of the Laboratory of Neural Circuits and Behavior at Rockefeller. "What is it that sets up this kind of handedness in the brain?"

Prior studies had shown that a gene involved in human migraine headaches (an asymmetrical affliction) was involved in this decision, but something was happening earlier that researchers had yet to figure out. Bargmann, who also is an investigator at the Howard Hughes Medical Institute, and postdoctoral associate Chiou-Fen Chuang -- now an assistant professor at Cincinnati Children's Research Foundation -- found that the first step of left-right communication is carried out by a gene that makes gap junctions. And yet strangely, as far as worm researchers knew, no gap junctions existed anywhere on adult worm AWC neurons.

Then Bargmann and Chuang had a flash of insight: Since, like handedness, AWC asymmetry arises before the animal is fully developed, maybe they needed to examine the nervous system of the embryonic worm. Using an electron microscope, they discovered that the developing worm's neural network, which had not previously been mapped, was completely different from that of the mature animal. "A large number of embryonic neurons are heavily interconnected by gap junctions," says Bargmann, who is also an HHMI Investigator. "They all grow to the midline, communicate with each other, and create a conduit of information that links together these two different sides of the brain." Then, after the gap junctions do their job, they disappear. "This network is transient; we only know about it because we were able to look at this early period."

A similar system of extensive gap junctions appears in the developing mammalian brain, but researchers have yet to figure out exactly what it does. In worms, at least, they now know that it's involved in differentiating the left and right sides. Now, Bargmann says, she's interested in finding out how this brief embryonic communication translates into a permanent change that lasts for the rest of the animal's life.

Source: Rockefeller University

Explore further: Manipulating wrinkles could lead to graphene semiconductors

Related Stories

Manipulating wrinkles could lead to graphene semiconductors

October 23, 2015

Graphene has generally been described as a two-dimensional structure—a single sheet of carbon atoms arranged in a regular structure—but the reality is not so simple. In reality, graphene can form wrinkles which make the ...

Phagraphene, a relative of graphene, discovered

September 3, 2015

A group of scientists from Russia, the USA and China have predicted the existence of a new two-dimensional carbon material via computer generated simulation, a "patchwork" analogue of graphene called phagraphene. The results ...

New multi-junction solar cell could break efficiency barrier

January 14, 2013

U.S. Naval Research Laboratory scientists in the Electronics Technology and Science Division, in collaboration with the Imperial College London and MicroLink Devices, Inc., Niles, Ill., have proposed a novel triple-junction ...

A single-sheet graphene p-n junction with two top gates

November 6, 2014

Researchers in Canada have designed and fabricated a single-sheet graphene p-n junction with two top gates. The standard technique, using a top and a bottom gate, can lead to damaging of the graphene layer. This is avoided ...

Recommended for you

How the finch changes its tune

August 3, 2015

Like top musicians, songbirds train from a young age to weed out errors and trim variability from their songs, ultimately becoming consistent and reliable performers. But as with human musicians, even the best are not machines. ...

Machine Translates Thoughts into Speech in Real Time

December 21, 2009

(PhysOrg.com) -- By implanting an electrode into the brain of a person with locked-in syndrome, scientists have demonstrated how to wirelessly transmit neural signals to a speech synthesizer. The "thought-to-speech" process ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.