Georgia tushev max planck biography
Abstract
N-glycosylation – the sequential addition of complex sugars to adhesion proteins, neurotransmitter receptors, ion channels and secreted trophic factors as they progress through the endoplasmic reticulum and the Golgi apparatus – is one of the most frequent protein modifications. In mammals, most organ-specific N-glycosylation events occur in the brain. Yet, little is known about the nature, function and regulation of N-glycosylation in neurons. Using imaging, quantitative immunoblotting and mass spectrometry, we show that hundreds of neuronal surface membrane proteins are core-glycosylated, resulting in the neuronal membrane displaying surprisingly high levels of glycosylation profiles that are classically associated with immature intracellular proteins. We report that while N-glycosylation is generally required for dendritic development and glutamate receptor surface expression, core-glycosylated proteins are sufficient to sustain these processes, and are thus functional. This atypical glycosylation of surface neuronal proteins can be attributed to a bypass or a hypo-function of the Golgi apparatus. Core-glycosylation is regulated by synaptic activity, modulates synaptic signaling and accelerates the turnover of GluA2-containing glutamate receptors, revealing a novel mechanism that controls the composition and sensing properties of the neuronal membrane.
https://doi.org/10.7554/eLife.20609.001eLife digest
Information is carried around the nervous system by cells called neurons. The ability of neurons to communicate with each other relies on many proteins that are found on the surfaces of the cells. Like in all animal cells, surface proteins are made inside the cell in a compartment called the endoplasmic reticulum. During this process, one or several complex sugar molecules are usually added to newly made proteins. These sugar molecules are then modified as the proteins leave the endoplasmic reticulum and pass through another compartment called
Abstract
Despite advances in methods to detect protein synthesis, it has not been possible to measure endogenous protein synthesis levels in vivo in an entire vertebrate brain. We developed a transgenic zebrafish line that allows for cell-type-specific labeling and imaging of nascent proteins in the entire animal. By replacing leucine with glycine in the zebrafish MetRS-binding pocket (MetRS-L270G), we enabled the cell-type-specific incorporation of the azide-bearing non-canonical-amino-acid azidonorleucine (ANL) during protein synthesis. Newly synthesized proteins were then labeled via 'click chemistry'. Using a Gal4-UAS-ELAV3 line to express MetRS-L270G in neurons, we measured protein synthesis intensities across the entire nervous system. We visualized endogenous protein synthesis and demonstrated that seizure-induced neural activity results in enhanced translation levels in neurons. This method allows for robust analysis of endogenous protein synthesis in a cell-type-specific manner, in vivo at single-cell resolution.
Research organism: Zebrafish
Introduction
Protein synthesis is critical for remodeling synaptic proteomes, especially when this process is associated with information storage (Sutton and Schuman, 2006). Chemical stimuli and changes in behavioral states alter protein expression in the nervous system. It has been shown in different model organisms that protein synthesis, during or shortly after learning, is essential for the formation of long-term memory (Davis and Squire, 1984; Agranoff et al., 1966; Agranoff and Klinger, 1964; Costa-Mattioli et al., 2009). Despite the importance of neuronal protein synthesis for many biological processes such as learning (Flexner et al., 1962; Hinz et al., 2013; Roberts et al., 2013), stress responses (Langebeck‐Jensen et al., 2019), and epilepsy (Brooks-Kayal et al., 1998; Hinz et al., 2012; Baraban et al., 2005; Del Bel et al., 1998), little is known about the endogenous neuronal protein synthesis levels Neurons exhibit spatial compartmentalization of gene expression where localization of messenger RNAs (mRNAs) to distal processes allows for site-specific distribution of proteins through local translation. Recently, there have been reports of coordination between mRNA transport with vesicular and organellar trafficking. In this review, we will highlight the latest literature on axonal and dendritic local protein synthesis with links to mRNA–organelle cotransport followed by emerging technologies necessary to study these phenomena. Recent high-resolution imaging studies have led to insights into the dynamics of RNA–organelle interactions, and we can now peer into these intricate interactions within subcellular compartments of neurons. Keywords: mRNA transport, mRNA translation, vesicular trafficking, organellar trafficking, single molecule imaging, high-resolution imaging, neurons Messenger RNAs (mRNAs) are distributed throughout subcellular compartments and subject to locally organized translation for the purpose of protein enrichment or sequestration. One clear advantage of transporting mRNAs is that the transcript can serve as a blueprint to rapidly produce multiple copies of the protein when and where the cell needs them. Targeting mRNAs to specific subcellular sites requires three major components. First, the cis-acting element(s) within the mRNA, referred to as the “localization element” or “zipcode,” are most frequently found in the 3′ untranslated region (UTR). Second, RNA-binding proteins (RBPs) function as trans-acting factors that recognize and bind to the cis-acting elements in a sequence-specific manner. Third, the resulting messenger ribonucleoprotein (mRNP) complex interacts with adaptor proteins that mediate active transport, anchoring, or translational silencing (Figure 1). Recent studies have uncovered the complexity among these components in directing localization in neurons. For example, the 3′UTR of localized .Abstract
Introduction