Mechanisms of Polarized Organelle Distribution in Neurons.

Dylan J Britt,Carlos M Guardia,Juan S Bonifacino,Ginny G Farías

doi:10.3389/fncel.2016.00088

Abstract

Neurons are highly polarized cells exhibiting axonal and somatodendritic domains with distinct complements of cytoplasmic organelles. Although some organelles are widely distributed throughout the neuronal cytoplasm, others are segregated to either the axonal or somatodendritic domains. Recent findings show that organelle segregation is largely established at a pre-axonal exclusion zone (PAEZ) within the axon hillock. Polarized sorting of cytoplasmic organelles at the PAEZ is proposed to depend mainly on their selective association with different microtubule motors and, in turn, with distinct microtubule arrays. Somatodendritic organelles that escape sorting at the PAEZ can be subsequently retrieved at the axon initial segment (AIS) by a microtubule- and/or actin-based mechanism. Dynamic sorting along the PAEZ-AIS continuum can thus explain the polarized distribution of cytoplasmic organelles between the axonal and somatodendritic domains.

Highlights

Among the first properties of neurons described by neuroanatomists was their polarization into distinct compartments—an axon, dendrites, and cell body or soma (Figure 1A; Deiters, 1865)
Neurites are further subdivided into branched, tapering dendrites and a single thin axon, which may extend for long distances before branching into terminals (Peters et al, 1991; Raine, 1999)
The soma and dendrites differ in shape, in terms of protein and organelle distribution the two are often treated as a unified somatodendritic domain

Summary

Mechanisms of Polarized Organelle Distribution in Neurons

Cell Biology and Neurobiology Branch, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA. Neurons are highly polarized cells exhibiting axonal and somatodendritic domains with distinct complements of cytoplasmic organelles. Some organelles are widely distributed throughout the neuronal cytoplasm, others are segregated to either the axonal or somatodendritic domains. Polarized sorting of cytoplasmic organelles at the PAEZ is proposed to depend mainly on their selective association with different microtubule motors and, in turn, with distinct microtubule arrays. Somatodendritic organelles that escape sorting at the PAEZ can be subsequently retrieved at the axon initial segment (AIS) by a microtubule- and/or actinbased mechanism. Dynamic sorting along the PAEZ-AIS continuum can explain the polarized distribution of cytoplasmic organelles between the axonal and somatodendritic domains.

INTRODUCTION

Polarized Organelle Distribution in Neurons