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.