Transcytosis of TrkA leads to diversification of dendritic signaling endosomes

Kelly Barford,Lloyd Mcmahon,Kathryn Mcdaniel,Christopher D Deppmann,Chan Choo Yap,Austin Keeler,Bettina Winckler

doi:10.1038/s41598-018-23036-8

Abstract

The development of the peripheral nervous system relies on long-distance signaling from target organs back to the soma. In sympathetic neurons, this long-distance signaling is mediated by target derived Nerve Growth Factor (NGF) interacting with its axonal receptor, TrkA. This ligand receptor complex internalizes into what is commonly referred to as the signaling endosome which is transported retrogradely to the soma and dendrites to mediate survival signaling and synapse formation, respectively. The molecular identity of signaling endosomes in dendrites has not yet been determined. Here, we perform a detailed analysis of TrkA endosomal compartments and trafficking patterns. We find that signaling endosomes are not uniform but molecularly diversified into Rab7 (late endosome) and Rab11 (recycling endosome) populations in axons and dendrites in vitro and in the soma in vivo. Surprisingly, TrkA-NGF signaling endosomes in dendrites undergo dynamic trafficking events, including putative fusion and fission. Overall, we find that signaling endosomes do not remain as a singular endosomal subtype but instead exist in multiple populations that undergo dynamic endosomal trafficking events. These dynamic events might drive functional diversification of the signaling endosome.

Highlights

The development of the sympathetic and sensory nervous systems requires the target derived neurotrophic factor, Nerve Growth Factor (NGF)[1]
We took advantage of sympathetic neurons isolated from FLAG-TrkA knock-in mice, TrkAFLAG/FLAG, which have a FLAG tag knocked into the endogenous TrkA locus in frame with the extracellular domain of the protein[10]
There are two possible pathways for how dendritic signaling endosomes are diversified into Rab11- or Rab7-positive endosomal pools: FLAG-TrkA might already be transported in multiple compartments in the axon to arrive in the soma diversified, or FLAG-TrkA is sorted within the somatodendritic region into two distinct endosomal populations after undergoing retrograde transcytosis

Summary

Introduction

The development of the sympathetic and sensory nervous systems requires the target derived neurotrophic factor, Nerve Growth Factor (NGF)[1]. No staining was observed in WT cultures, demonstrating that the antibody does not enter axons non- (Supplementary Figure 1C) and can be used to faithfully track NGF-TrkA SEs. we have developed advanced quantification techniques to analyze endosomal co-localization.

Results

Conclusion