Close

SorCS1-mediated Sorting of Neurexin in Dendrites Maintains Presynaptic Function

Luis Filipe Ribeiro, Ben Verpoort, Julie Nys, Kristel M Vennekens, Keimpe D Wierda, Joris de Wit

Preprint posted on 17 February 2019 https://www.biorxiv.org/content/10.1101/552695v1

Article now published in PLOS Biology at http://dx.doi.org/10.1371/journal.pbio.3000466

What mechanisms instruct axon-dendritic polarity of neurons? The dendritic sorting receptor SorCS1 maintains cell compartment-specific protein composition.

Selected by Carmen Adriaens

Categories: cell biology, neuroscience

Background

Neurons are polarized cells with two distinct compartments: dendrites and axons. These contain the post-and pre-synaptic specialization, respectively, which vary greatly in protein composition. Proper neuronal development, neuronal function and neuronal plasticity depend on the precise targeting of proteins to the right compartment. The bulk of protein synthesis in neurons occurs at the cell body. Thus, a central conundrum in Neuroscience remains: how are axonal and dendritic proteins differentially located to distinct compartments within the same cell?

Neurons have developed different mechanisms to ensure proper axonal protein targeting1. For instance, when protein subcellular distribution initially happens in a non-discriminatory fashion, protein cargo can be removed exclusively from the dendritic surface through a mechanism called selective endocytosis/retention2. As a result, protein cargo becomes enriched at the axonal surface. Alternatively, axonal cargo can be first inserted into the somatodendritic plasma membrane, and only then internalized from the cell surface and rerouted via endosomally derived carriers to the axon through a mechanism called transcytosis2.

In this preprint, Ribeiro et al. examined the role of the sorting receptor SorCS1 in the transcytosis-mediated axonal targeting of Neurexin (Nrxn), a presynaptic cell adhesion molecule essential for synaptogenesis and neuronal transmission3. SorCS1 belongs to the family of VPS10P-domain sorting receptors4, which are prominently expressed in the brain. They have recently emerged as key regulators of intracellular trafficking of synaptic receptors5–7 , but the mechanism through which they do this is yet uncharacterized. Here, Ribeiro and colleagues elucidate part of the cellular and molecular mechanisms that SorCS proteins use to regulate the trafficking of synaptic receptors.

 

Key Findings

First, the authors show that the axonal surface of mature cortical primary neurons displays twice as much endogenous Nrxn1a as the dendritic surface, indicating polarization towards the axon (see figure below). However, when the cells are permeabilized, Nrxn1a is mostly detected in dendrites. Permeabilization makes it possible to detect also intracellular proteins, indicating that Nrxn1a is trafficked to both compartments. To understand the mechanism responsible for axonal polarization of Nrxn1α the authors performed live-cell imaging experiments to monitor the transport of Nrxn1a throughout the secretory pathway. They showed that Nrxn1a is first trafficked to dendrites, appearing in the axon only after a long delay. Thus, they hypothesized that newly synthesized Nrxn1a is first trafficked to the somatodendritic compartment, where it is inserted into the plasma membrane. Indeed, when they monitored endocytosis, Nrxn1a was internalized from this membrane and further transcytosed, through the cell, from the dendritic surface to the axonal compartment.

Figure. (a) Surface endogenous Nrxn1a is axonally polarized in mouse cortical neurons. Red arrowheads indicate the axon and blue asterisks mark the cell body. (b) ratio of the axonal/dendritic HA intensity. DIV, days in vitro. Figure adapted from the preprint figure 3 by Ribeiro et al. made available under a CC-BY-NC-ND 4.0 International license.

 

One factor that could be involved in this process is SorCS1, an endosomal sorting receptor that cycles between the plasma membrane and the endosomal pathway4. Indeed, as previous work had shown that SorCS1 directly binds Nrxn in cis7, the authors tested whether this protein was required for Nrxn1α transcytosis. Loss of SorCS1 resulted in an accumulation of Nrxn1a on the dendritic surface and its depletion from the axonal surface, shifting Nrxn1α surface polarization from axonal to dendritic. This polarization defect was due to an impaired transition of internalized Nrxn1a from early endosomes (EEs) to recycling endosomes (REs) in the somatodendritic compartment. Normally, upon internalization from the dendritic plasma membrane, cargo proteins are incorporated into small carrier vesicles that fuse with existing EEs. From EEs, cargo is sorted to REs. When this transition is affected (like in the case of SorCS1 loss), cargo accumulates in EE, and is either degraded via lysosomes or recycled back to the dendritic membrane.

To gain more mechanistic insight into how SorCS1 functions, the authors set out to find factors that interact with this protein. They identified the endosomal associated protein, Rip11, as a new SorCS1 binding partner. Rip11 has been previously involved in sorting of cargo from early to recycling endosomes in non-neuronal cells, and here they showed that it is also required to maintain axon-dendritic polarity of Nrxn1a.

With these findings in mind, Ribeiro et al. proposed that SorCS1 and Rip11 form a protein complex that localizes to dendritic endosomes and sorts internalized Nrxn1α from early to recycling endosomes. This could explain the increase in surface dendritic levels of Nrxn1α and the concomitant decrease in surface axonal levels observed in Sorcs1 KO cells.

Finally, the authors tested the impact of genetic ablation of SorCS1, which decreases the axonal surface targeting of Nrxn1a, on Nrxn-dependent neuronal transmission and synaptogenesis. Indeed, depletion of SorCS1 compromised Nrxn-dependent synapse assembly and neuronal transmission. In summary, these findings expand the list of neuronal cargoes that undergo transcytosis, which so far is very limited2, and support the notion that SorCS1-mediated sorting in dendrites is required to maintain axon-dendritic polarity and normal neuronal function.

 

What do I think about this preprint / Open Questions?

I like this preprint a lot! It is a detailed study, and carefully performed. One experiment I particularly like, and that I think should become more common in cell biology research, is the endogenous tagging of proteins using CRISPR/Cas9. For instance, with this technique, the authors showed that Nrxn1α does not only localize to axons, but could also be found (albeit potentially temporarily) in the dendrites. As such, the authors could overcome the lack of good antibodies, and used these observations as the basis for their study. In addition, the live-cell imaging experiments in this work are very impressive. I thought the videos of cargo trafficking from one cellular compartment to the other in real life were awesome!

However, these observations also raise some questions that, in the future, may need further clarification. For instance, what is the biological function of the dendritic pool of Nrxn? Is dendritic Nrxn merely a reservoir of readily-synthesized protein to be delivered to the axonal membrane, or does dendritically localized Nrxn have a function in the dendritic compartment? As dendritic/postsynaptically expressed Nrxn has been shown to inhibit synapse formation8, it would be interesting to further study other possible functions of dendritic Nrxn, particularly of intracellular Nrxn, which is abundantly present in dendrites.

One important finding is that the axonal-dendritic balance of Nrxn is regulated by neuronal activity. Does this mean that SorCS1-mediated sorting can dynamically regulate Nrxn polarity? How do neuronal activity and SorCS1-mediated sorting of Nrxn crosstalk in order to ensure proper protein distribution and neuronal functioning? And further, how much can these Nrxn-specific observations be generalized to explain neuronal activity-dependent compartment diversification?

In summary, I think this study provides important insights into the mechanisms controlling the intracellular trafficking of a compartmentally polarized protein, which helps to better understand subcellular protein distribution in polarized cells. With the toolbox the authors developed for this study, I am convinced many more questions can be answered, and thus I look forward to read the follow up stories, too!

 

References

  1. Bentley, M. & Banker, G. Nat. Rev. Neurosci. 17, 611–622 (2016).
  2. Winckler, B. & Mellman, I. Cold Spring Harb. Perspect. Biol. 2, a001826–a001826 (2010).
  3. Südhof, T.C. Cell 171, 745–769 (2017).
  4. Willnow, T.E., Petersen, C.M. & Nykjaer, A. Nat. Rev. Neurosci. 9, 899–909 (2008).
  5. Ma, Q. et al. JCI Insight 2, (2017).
  6. Glerup, S. et al. Mol. Psychiatry 21, 1740–1751 (2016).
  7. Savas, J.N. et al. Neuron 87, 764–780 (2015).
  8. Taniguchi, H. et al. J. Neurosci. 27, 2815–2824 (2007).

 

 

Tags: axonal targeting, cell biology, cell compartment specialization, intracellular trafficking, neurexins, neuroscience, sorcs1, transcytosis

Posted on: 27 February 2019

doi: https://doi.org/10.1242/prelights.8991

Read preprint (No Ratings Yet)

Author's response

Luis Ribeiro shared

Thank you for highlighting our work!

 

Q1: Is dendritic Nrxn merely a reservoir of readily-synthesized protein to be delivered to the axonal membrane, or does dendritically localized Nrxn have a function in the dendritic compartment?

Perhaps one of the most puzzling issues that remains to be addressed is the biological function of this circuitous transcytotic trafficking route. One hypothesis that has been put forward is that transcytosis in neurons provides an efficient way of delivering receptors from a reservoir of readily-synthesized proteins (Winckler and Mellman, 2010). Like it has been suggested for other transcytotic axonal cargoes, either constitutively (Ascano et al., 2009; Leterrier, 2006) or in response to ligand-receptor interactions and signalling (Ascano et al., 2009; Yamashita et al., 2017), a dendritic pool of Nrxn may sustain the demand for receptors along the axonal surface. In agreement, neurotrophin signalling (initiated in axon terminals) is necessary for the transport of new TrkA receptors originated from the somatodendritic plasma membrane via transcytosis, increasing receptor availability along the axonal surface (Ascano et al., 2009; Yamashita et al., 2017).

 

As you point out in the prelight, dendritically/postsynaptically localized Nrxn might also have a function in this compartment. So far, few hints in the literature have provided insights into a possible postsynaptic function of Nrxns at mammalian CNS synapses. One group suggested that postsynaptic Nrxn1 might interact with Nlgn1 in cis, thereby preventing trans-synaptic interactions of Nlgn1 with presynaptic Nrxn1 (“cis-inhibition hypothesis”). In agreement, postsynaptic expression (cell-autonomous) of Nrxn1 decreased the Nlgn1-dependent synaptogenic activity, reducing synapse density in vitro (Taniguchi et al., 2007). Rather than influencing synaptogenesis, others uncovered a role for postsynaptic Nrxns in NMDA receptor function. Although the exact mechanisms were not fully elucidated, the observed reduction in NMDA receptor-dependent postsynaptic currents in alpha Nrxns KO slices was shown to be cell-autonomous and likely reflects a change in the postsynaptic localization of NMDA receptors (Kattenstroth et al., 2004). Additionally, at the C. elegans neuromuscular junction, the ectodomain of postsynaptic Nrxn is proteolytically cleaved and binds to the presynaptic α2δ calcium channel subunit to inhibit presynaptic release (Tong et al., 2017). In summary, we cannot currently provide a definitive answer, but as suggested by the literature, it may very well be that Nrxns are first trafficked to dendrites, where they can provide a reservoir of Nrxn for the axonal membrane and/or modulate synaptogenesis and postsynaptic receptor function.

 

Q2: How do neuronal activity and SorCS1-mediated of Nrxn crosstalk in order to ensure proper protein distribution and neuronal functioning? How much can these Nrxn-specific observations be generalized to explain neuronal activity-dependent compartment diversification?

 

Although these are very interesting questions, we cannot currently answer them. Experimentally, we could show that a chronic increase in neuronal firing activity shifts the axonal/dendritic balance of Nrxn from axonal to dendritic. On the other hand, tetradotoxin (TTX) treatment, which decreases neuronal firing activity, augmented the axonal surface polarization of Nrxn. These observations nicely support a model in which neurons can dynamically change the axonal/dendritic surface balance of Nrxn in response to bidirectional changes in activity. However, if these bidirectional changes in neuronal activity can control neuronal compartmentalized distribution of other polarized proteins, to my knowledge, has never been tested. Interestingly, in Sorcs1 KO cells TTX treatment failed to increase the axonal surface polarization of Nrxn, which suggests that SorCS1-mediated sorting is required for TTX-dependent increase in axonal surface levels of Nrxn. Future work is required to understand how neuronal activity regulates SorCS1-dependent transcytosis of Nrxn.

 

References:

Ascano, M., Richmond, A., Borden, P., and Kuruvilla, R. (2009). Axonal Targeting of Trk Receptors via Transcytosis Regulates Sensitivity to Neurotrophin Responses. J. Neurosci. 29, 11674–11685.

Kattenstroth, G., Tantalaki, E., Sudhof, T.C., Gottmann, K., and Missler, M. (2004). Postsynaptic N-methyl-D-aspartate receptor function requires -neurexins. Proc. Natl. Acad. Sci. 101, 2607–2612.

Leterrier, C. (2006). Constitutive Activation Drives Compartment-Selective Endocytosis and Axonal Targeting of Type 1 Cannabinoid Receptors. J. Neurosci. 26, 3141–3153.

Taniguchi, H., Gollan, L., Scholl, F.G., Mahadomrongkul, V., Dobler, E., Limthong, N., Peck, M., Aoki, C., and Scheiffele, P. (2007). Silencing of Neuroligin Function by Postsynaptic Neurexins. J. Neurosci. 27, 2815–2824.

Tong, X.-J., López-Soto, E.J., Li, L., Liu, H., Nedelcu, D., Lipscombe, D., Hu, Z., and Kaplan, J.M. (2017). Retrograde Synaptic Inhibition Is Mediated by α-Neurexin Binding to the α2δ Subunits of N-Type Calcium Channels. Neuron 95, 326-340.e5.

Winckler, B., and Mellman, I. (2010). Trafficking Guidance Receptors. Cold Spring Harb. Perspect. Biol. 2, a001826–a001826.

Yamashita, N., Joshi, R., Zhang, S., Zhang, Z.-Y., and Kuruvilla, R. (2017). Phospho-Regulation of Soma-to-Axon Transcytosis of Neurotrophin Receptors. Dev. Cell 42, 626-639.e5.

 

Have your say

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Sign up to customise the site to your preferences and to receive alerts

Register here

preLists in the cell biology category:

‘In preprints’ from Development 2022-2023

A list of the preprints featured in Development's 'In preprints' articles between 2022-2023

 



List by Alex Eve, Katherine Brown

preLights peer support – preprints of interest

This is a preprint repository to organise the preprints and preLights covered through the 'preLights peer support' initiative.

 



List by preLights peer support

The Society for Developmental Biology 82nd Annual Meeting

This preList is made up of the preprints discussed during the Society for Developmental Biology 82nd Annual Meeting that took place in Chicago in July 2023.

 



List by Joyce Yu, Katherine Brown

CSHL 87th Symposium: Stem Cells

Preprints mentioned by speakers at the #CSHLsymp23

 



List by Alex Eve

Journal of Cell Science meeting ‘Imaging Cell Dynamics’

This preList highlights the preprints discussed at the JCS meeting 'Imaging Cell Dynamics'. The meeting was held from 14 - 17 May 2023 in Lisbon, Portugal and was organised by Erika Holzbaur, Jennifer Lippincott-Schwartz, Rob Parton and Michael Way.

 



List by Helen Zenner

9th International Symposium on the Biology of Vertebrate Sex Determination

This preList contains preprints discussed during the 9th International Symposium on the Biology of Vertebrate Sex Determination. This conference was held in Kona, Hawaii from April 17th to 21st 2023.

 



List by Martin Estermann

Alumni picks – preLights 5th Birthday

This preList contains preprints that were picked and highlighted by preLights Alumni - an initiative that was set up to mark preLights 5th birthday. More entries will follow throughout February and March 2023.

 



List by Sergio Menchero et al.

CellBio 2022 – An ASCB/EMBO Meeting

This preLists features preprints that were discussed and presented during the CellBio 2022 meeting in Washington, DC in December 2022.

 



List by Nadja Hümpfer et al.

Fibroblasts

The advances in fibroblast biology preList explores the recent discoveries and preprints of the fibroblast world. Get ready to immerse yourself with this list created for fibroblasts aficionados and lovers, and beyond. Here, my goal is to include preprints of fibroblast biology, heterogeneity, fate, extracellular matrix, behavior, topography, single-cell atlases, spatial transcriptomics, and their matrix!

 



List by Osvaldo Contreras

EMBL Synthetic Morphogenesis: From Gene Circuits to Tissue Architecture (2021)

A list of preprints mentioned at the #EESmorphoG virtual meeting in 2021.

 



List by Alex Eve

FENS 2020

A collection of preprints presented during the virtual meeting of the Federation of European Neuroscience Societies (FENS) in 2020

 



List by Ana Dorrego-Rivas

Planar Cell Polarity – PCP

This preList contains preprints about the latest findings on Planar Cell Polarity (PCP) in various model organisms at the molecular, cellular and tissue levels.

 



List by Ana Dorrego-Rivas

BioMalPar XVI: Biology and Pathology of the Malaria Parasite

[under construction] Preprints presented at the (fully virtual) EMBL BioMalPar XVI, 17-18 May 2020 #emblmalaria

 



List by Dey Lab, Samantha Seah

1

Cell Polarity

Recent research from the field of cell polarity is summarized in this list of preprints. It comprises of studies focusing on various forms of cell polarity ranging from epithelial polarity, planar cell polarity to front-to-rear polarity.

 



List by Yamini Ravichandran

TAGC 2020

Preprints recently presented at the virtual Allied Genetics Conference, April 22-26, 2020. #TAGC20

 



List by Maiko Kitaoka et al.

3D Gastruloids

A curated list of preprints related to Gastruloids (in vitro models of early development obtained by 3D aggregation of embryonic cells). Updated until July 2021.

 



List by Paul Gerald L. Sanchez and Stefano Vianello

ECFG15 – Fungal biology

Preprints presented at 15th European Conference on Fungal Genetics 17-20 February 2020 Rome

 



List by Hiral Shah

ASCB EMBO Annual Meeting 2019

A collection of preprints presented at the 2019 ASCB EMBO Meeting in Washington, DC (December 7-11)

 



List by Madhuja Samaddar et al.

EMBL Seeing is Believing – Imaging the Molecular Processes of Life

Preprints discussed at the 2019 edition of Seeing is Believing, at EMBL Heidelberg from the 9th-12th October 2019

 



List by Dey Lab

Autophagy

Preprints on autophagy and lysosomal degradation and its role in neurodegeneration and disease. Includes molecular mechanisms, upstream signalling and regulation as well as studies on pharmaceutical interventions to upregulate the process.

 



List by Sandra Malmgren Hill

Lung Disease and Regeneration

This preprint list compiles highlights from the field of lung biology.

 



List by Rob Hynds

Cellular metabolism

A curated list of preprints related to cellular metabolism at Biorxiv by Pablo Ranea Robles from the Prelights community. Special interest on lipid metabolism, peroxisomes and mitochondria.

 



List by Pablo Ranea Robles

BSCB/BSDB Annual Meeting 2019

Preprints presented at the BSCB/BSDB Annual Meeting 2019

 



List by Dey Lab

MitoList

This list of preprints is focused on work expanding our knowledge on mitochondria in any organism, tissue or cell type, from the normal biology to the pathology.

 



List by Sandra Franco Iborra

Biophysical Society Annual Meeting 2019

Few of the preprints that were discussed in the recent BPS annual meeting at Baltimore, USA

 



List by Joseph Jose Thottacherry

ASCB/EMBO Annual Meeting 2018

This list relates to preprints that were discussed at the recent ASCB conference.

 



List by Dey Lab, Amanda Haage

Also in the neuroscience category:

‘In preprints’ from Development 2022-2023

A list of the preprints featured in Development's 'In preprints' articles between 2022-2023

 



List by Alex Eve, Katherine Brown

CSHL 87th Symposium: Stem Cells

Preprints mentioned by speakers at the #CSHLsymp23

 



List by Alex Eve

Journal of Cell Science meeting ‘Imaging Cell Dynamics’

This preList highlights the preprints discussed at the JCS meeting 'Imaging Cell Dynamics'. The meeting was held from 14 - 17 May 2023 in Lisbon, Portugal and was organised by Erika Holzbaur, Jennifer Lippincott-Schwartz, Rob Parton and Michael Way.

 



List by Helen Zenner

FENS 2020

A collection of preprints presented during the virtual meeting of the Federation of European Neuroscience Societies (FENS) in 2020

 



List by Ana Dorrego-Rivas

ASCB EMBO Annual Meeting 2019

A collection of preprints presented at the 2019 ASCB EMBO Meeting in Washington, DC (December 7-11)

 



List by Madhuja Samaddar et al.

SDB 78th Annual Meeting 2019

A curation of the preprints presented at the SDB meeting in Boston, July 26-30 2019. The preList will be updated throughout the duration of the meeting.

 



List by Alex Eve

Autophagy

Preprints on autophagy and lysosomal degradation and its role in neurodegeneration and disease. Includes molecular mechanisms, upstream signalling and regulation as well as studies on pharmaceutical interventions to upregulate the process.

 



List by Sandra Malmgren Hill

Young Embryologist Network Conference 2019

Preprints presented at the Young Embryologist Network 2019 conference, 13 May, The Francis Crick Institute, London

 



List by Alex Eve
Close