UC Davis researchers visualize formation of a new synapse

'Movie' shows dynamics of molecule implicated in autism

(SACRAMENTO, Calif.) — A protein called neuroligin that is implicated in some forms of autism is critical to the construction of a working synapse, locking neurons together like "molecular Velcro," a study lead by a team of UC Davis researchers has found.

Published online in the June issue of the journal Neural Development, the study is accompanied by groundbreaking images that are the first to show two neurons coming together using neuroligin to construct a new synapse.

"Previous research has suggested that neuroligin is critical for the formation and stabilization of synapses," said Kimberley McAllister, an associate professor of neurology in the UC Davis School of Medicine and a researcher at the UC Davis Center for Neuroscience. "Our work suggests that neuroligin is one of the first molecules to be recruited to new synapses and that it also acts as Velcro to strengthen those new connections."

Neuroligin is a member of a family of four protein molecules that bind to another family of proteins, the β-neurexins, across synapses. During the past decade, scientists have observed that neuroligin is critical for synapse formation and function, but it is only recently that a link between the two synapse-forming molecules and autism has been recognized, McAllister said.

Lead study author and UC Davis postdoctoral fellow Stephanie Barrow said that researchers had hypothesized that neuroligin could facilitate the recruitment of other proteins important in building synapses, but no one had been able to directly visualize the process. That's because synapses are less than 1 micron wide — 100 times narrower than a strand of human hair. To view the process, the researchers cultured neurons taken from newly born rats and flourescently labled the proteins —neuroligin, PSD-95 and NMDA — which are critical to synapse formation.

"We are the first to observe that neuroligin zips around dendrites (the branched projections of neurons) before synapses form and can accumulate very soon after contact between cells," Barrow said.

Barrow described what the team was able to visualize: