In vivo assembly of the axon initial segment in motor neurons

1. Brain Struct Funct. 2014 Jul;219(4):1433-50. doi: 10.1007/s00429-013-0578-7.
Epub 2013 Jun 2.

In vivo assembly of the axon initial segment in motor neurons.

Le Bras B(1), Fréal A, Czarnecki A, Legendre P, Bullier E, Komada M, Brophy PJ,
Davenne M, Couraud F.

Author information:
(1)INSERM, UMRS 952, 9 Quai St Bernard, 75005, Paris, France.

The axon initial segment (AIS) is responsible for both the modulation of action
potentials and the maintenance of neuronal polarity. Yet, the molecular
mechanisms controlling its assembly are incompletely understood. Our study in
single electroporated motor neurons in mouse embryos revealed that AnkyrinG
(AnkG), the AIS master organizer, is undetectable in bipolar migrating motor
neurons, but is already expressed at the beginning of axonogenesis at E9.5 and
initially distributed homogeneously along the entire growing axon. Then, from
E11.5, a stage when AnkG is already apposed to the membrane, as observed by
electron microscopy, the protein progressively becomes restricted to the
proximal axon. Analysis on the global motor neurons population indicated that
Neurofascin follows an identical spatio-temporal distribution, whereas sodium
channels and β4-spectrin only appear along AnkG(+) segments at E11.5. Early
patch-clamp recordings of individual motor neurons indicated that at E12.5 these
nascent AISs are already able to generate spikes. Using knock-out mice, we
demonstrated that neither β4-spectrin nor Neurofascin control the
distal-to-proximal restriction of AnkG.

DOI: 10.1007/s00429-013-0578-7
PMCID: PMC4072062
PMID: 23728480 [Indexed for MEDLINE]

Auteurs Bordeaux Neurocampus