Information in the brain travels along neuronal axons that form junctions, or ‘synapses’, with tree-like dendrites of other neurons. Normally, the myriad of neuronal pathways develop into highly organized layers called lamina—distinct areas where axons physically meet dendrites, providing a structural basis for integrating information. How such patterning of neurons actually occurs has long eluded brain scientists.
Now, a team led by Shigeyoshi Itohara at the Brain Science Institute in Wako, has determined that adhesion molecules on terminally projecting axons instruct the laminar configuration within ‘target’ dendrites—branches of neurons that receive signals from axons (1). The researchers found that individual dendrites are divided molecularly and functionally into ‘sub-dendritic segments’, each of which corresponds to information input from a specific group of axons.
Netrin-G1 and netrin-G2 belong to a family of molecules that promote attraction between cells. Previous studies have demonstrated that netrin-G1 and -G2 proteins bind specific receptors, NGL-1 and NGL-2, respectively. Itohara’s team initially demonstrated selective expression of netrin-G1 and -G2 on axons that project onto individual layers of the brain cortex and hippocampus (Fig. 1); even layers physically juxtaposed to one another express only one of the netrin-G proteins. Interestingly, the team also found similar laminar patterns of netrin-G partner proteins NGL-1 and NGL-2 on target dendrites.
These one-to-one expression patterns of netrin-G and NGL protein suggested that a ‘lock-and-key’ configuration of the proteins might account for lamina-specific organization within sub-dendritic segments. To address this possibility, the team analyzed mice lacking either netrin-G1 or -G2 and found, surprisingly, disruption of laminar neuronal patterns but normal gross brain structure and arrangements of neurons. Closer examination revealed that in the absence of its netrin-G partner, the cognate NGL protein was now distributed diffusely along a given dendrite rather than restricted to a specific segment.
Itohara and team concluded that the interaction between axon-expressed netrin-G and dendrite-expressed NGL functionally and physically divides dendrites into segments. In other words, ‘trans-neuronal’ mechanisms, rather than cell-intrinsic factors, account for neuronal circuit specificity within a single neuron.
“We are working hard to investigate the role of netrin-G/NGL interactions on structure and function of the neurons, and to understand how netrin-G1- and -G2-dependent neuronal circuits integrate information,” says Itohara. For now, the team’s data point to an essential role for netrin-G/NGL interactions in determining specific interaction between axon projections and dendrites, which give the characteristic laminar organization of the brain.
1. Nishimura-Akiyoshi, S., Niimi, K., Nakashiba, T. & Itohara, S. Axonal netrin-Gs transneuronally determine lamina-specific subdendritic segments. Proceedings of the National Academy of Sciences USA 104, 14801–14806 (2007).
Single-stranded DNA and RNA origami go live
15.12.2017 | Wyss Institute for Biologically Inspired Engineering at Harvard
New antbird species discovered in Peru by LSU ornithologists
15.12.2017 | Louisiana State University
DNA molecules that follow specific instructions could offer more precise molecular control of synthetic chemical systems, a discovery that opens the door for engineers to create molecular machines with new and complex behaviors.
Researchers have created chemical amplifiers and a chemical oscillator using a systematic method that has the potential to embed sophisticated circuit...
MPQ scientists achieve long storage times for photonic quantum bits which break the lower bound for direct teleportation in a global quantum network.
Concerning the development of quantum memories for the realization of global quantum networks, scientists of the Quantum Dynamics Division led by Professor...
Researchers have developed a water cloaking concept based on electromagnetic forces that could eliminate an object's wake, greatly reducing its drag while...
Tiny pores at a cell's entryway act as miniature bouncers, letting in some electrically charged atoms--ions--but blocking others. Operating as exquisitely sensitive filters, these "ion channels" play a critical role in biological functions such as muscle contraction and the firing of brain cells.
To rapidly transport the right ions through the cell membrane, the tiny channels rely on a complex interplay between the ions and surrounding molecules,...
The miniaturization of the current technology of storage media is hindered by fundamental limits of quantum mechanics. A new approach consists in using so-called spin-crossover molecules as the smallest possible storage unit. Similar to normal hard drives, these special molecules can save information via their magnetic state. A research team from Kiel University has now managed to successfully place a new class of spin-crossover molecules onto a surface and to improve the molecule’s storage capacity. The storage density of conventional hard drives could therefore theoretically be increased by more than one hundred fold. The study has been published in the scientific journal Nano Letters.
Over the past few years, the building blocks of storage media have gotten ever smaller. But further miniaturization of the current technology is hindered by...
11.12.2017 | Event News
08.12.2017 | Event News
07.12.2017 | Event News
15.12.2017 | Power and Electrical Engineering
15.12.2017 | Materials Sciences
15.12.2017 | Life Sciences