Uncovering the machinery for the sorting of newly synthesized proteins into the axon

Projektbeschreibung

Ein alternativer Weg der Proteinsortierung in Neuronen wird entschlüsselt

Neu synthetisierte Transmembranproteine gelangen über das raue endoplasmatische Retikulum und den Golgi-Apparat in die Plasmamembran. Doch noch ist unklar, ob die Proteinsortierung in den Axonen der Nervenzellen demselben Weg folgt oder den Golgi-Apparat umgeht. Das EU-finanzierte Projekt NEUROSORTER will die Mechanismen eruieren, die für die polarisierte Verteilung von Proteinen in Neuronen verantwortlich sind, da diese für deren Funktionieren essenziell ist. Das Forschungsteam wird die Sortierwege neu synthetisierter Axonproteine mit Hilfe von Bildgebung in räumlich-zeitlicher Auflösung und Massenspektrometrie nachvollziehen. Die Ergebnisse liefern wichtige Erkenntnisse über die Existenz alternativer Wege der Proteinsortierung in Neuronen und ermöglichen ein tieferes Verständnis von Erkrankungen, die mit diesem Pfad zusammenhängen.

Ziel

Neuronal development and function rely on the polarized distribution of organelles and transmembrane proteins (cargoes) across their somatodendritic and axonal domains. However, it is unknown how organelle organization regulates the polarized sorting of transmembrane proteins to ensure proper neuronal function.

The classical model for sorting of newly synthesized transmembrane proteins to the plasma membrane (PM) follows the biosynthetic pathway via the rough endoplasmic reticulum (ER) and Golgi, which are restricted to the somatodendritic domain in neurons. It is unclear whether this classical secretion pathway is the main route for cargo sorting into the axon or whether an alternative route to the axon is used for most axonal cargoes. Intriguingly, evidence indicates that cargoes can bypass the Golgi for their sorting to the axonal PM. However, the identity of an unconventional secretory pathway has not been demonstrated yet. Here, I propose that selective machinery, including the axonal ER and undefined intermediate compartments, allows local axonal cargo secretion.

Previously, I advanced our knowledge on Golgi-dependent sorting of somatodendritic cargoes and elucidated the mechanisms behind ER organization in neurons. Here, for the first time we will:
1) Identify the sorting routes for newly synthesized axonal proteins
2) Unravel the machinery required for Golgi-independent cargo sorting into the axon, and
3) Elucidate its impact on neuronal development and function

We will use high spatio-temporal resolution imaging and mass-spectrometry combined with novel strategies to control and track cargo secretion, as well as proximity-based labeling to identify key players in the newly identified machinery.

A broad spectrum of human diseases is associated to cargo Golgi-bypass. Neurons offer a unique advantage in spatial resolution to characterize this unconventional route, which could play a key role in human health and disease.