Compartmentalization within neurites: its mechanisms and implications

Neurons are morphologically characterized by long processes extending from a cell body. These processes, the dendrites and axon, are major sub-cellular compartments defined by morphological, molecular, and functional differences. However, evidence from vertebrates and invertebrates suggests that, based on molecular distribution, individual axons and dendrites are further divided into distinct compartments; many membrane molecules involved in axon guidance and synapse formation are localized to specific segments of axons or dendrites that share a boundary of localization. In this review, we describe recent progress in understanding the mechanisms of intra-neurite patterning, and discuss its potential roles in the development and function of the nervous system. Each protein employs different ways to achieve compartment-specific localization; some membrane molecules localize via cell-autonomous ability of neurons, while others require extrinsic signals for localization. The underlying regulatory mechanisms include transcriptional regulation, local translation, diffusion barrier, endocytosis, and selective membrane targeting. We propose that intra-neurite compartmentalization could provide platforms for structural and functional diversification of individual neurons.