Scientists question a popular theory about how the nervous system trims its branches
As tiny embryos in the womb, we start out with a lot more neuronal material than we actually need. During development, the body drastically prunes back the excess—cutting the branches from nerve cell bodies, known as axons, as well as entire neurons.
Scientists have long assumed that the decision whether to cull or keep an axon was coordinated by the axon itself, rather than by the cell body from which it extends. In recent years, tantalizing clues from several research groups have challenged that assumption. Now researchers at The Rockefeller University have proven that the cell body actively controls axon degeneration, and have uncovered many of the molecular details that allow this long-range communication.
In a report published online in Cell, they report that the instructions telling axons in developing embryos whether to live or die come from the cell body, not the axon. “This is a surprising finding,” notes senior author Marc Tessier-Lavigne, president of Rockefeller University and the Carson Family Professor and head of the Laboratory of Brain Development and Repair. “When the axon senses a ‘distress signal’—a lack of a growth factor called NGF—it doesn’t make the decision to degenerate by itself. It actually sends the information to the cell body, which is quite far away, and the cell body sends its decision back down the axon.”
Source & further reading:
http://newswire.rockefeller.edu/2016/02/18/scientists-question-a-popular-theory-about-how-the-nervous-system-trims-its-branches/
Paper:
http://www.cell.com/cell/abstract/S0092-8674(16)30046-0
Image:
Axons of normal neurons, shown on top, degenerate when deprived of NGF. However, the axons of neurons that lack the protein Puma remain intact (shown below), indicating that their degeneration is controlled by Puma and the cell body.
#neuroscience #axons #neurons #research
I think this is interesting and surprising because the chemical diffusion time from an axon to the cell body (and back!) is really slow. I thought I remembered times measured in days. (Presumably in a fetus it would be a lot faster, though, since it's not two meters tall.)
ReplyDeleteI'm much more surprised by "who's in charge" than the timing.
ReplyDeleteI've been working my way through the harvard neurobiology course at https://www.mcb80x.org/ and they talk a lot about local control and axonal signal summing. Apparently there's a ton of stuff going on out there -- which, again, at that distance from the nucleus, is weird.
ReplyDeleteThe cell body... therefore likely the nucleus?
ReplyDeleteAnd then the cell's logic gates transmit then receive their Boolean function from the controller brain which is connected by cosmic strings to the universal mainframe. O.o
ReplyDelete