Role of Ectosomes in the Design of the Myelinated Axon: Structural Find

Abstract

The evolution of vertebrates required an energy efficient mechanism of fast nerve conduction. Two events: formation of a myelin sheath ­– an insulator ­– and a segmented mode of covering the axon by myelin fulfilled this need. This arrangement, coordinated by oligodendrocytes and neurons, generates saltatory nerve conduction, but the mechanism is indeterminate. Disruption of this structure impairs nervous system function. We performed a developmental study of embryonic avian optic nerve, using transmission electron microscopy and 3D-electron tomography. We present structural evidence – in vivo – of three sequential events that set a platform for oligodendrocyte/neuron communication. First, they embrace, thereby positioning their plasma membranes face to face; second, they create a shared compartment for interchanging information; third, they release and exchange ectosomes to, we posit, transduce signals for structuring the myelinated axon. These data identity the earliest developments following oligodendrocyte/neuron encounter, set the stage to identifying their cross-talk and searching for the aetiology of nervous system diseases.