Biology subjects

Valbuena, F. M.

Publications and source records attributed to Valbuena, F. M..

3 recordsLinked to original sources

bioRxiv2021

Activity-dependent Golgi satellite formation in dendrites reshapes the neuronal surface glycoproteome

Activity-driven changes in the neuronal surface glycoproteome are known to occur with synapse formation, plasticity and related diseases, but their mechanistic basis and significance are unclear. Here, we observed that N-glycans on surface glycoproteins of dendrites shift from immature to mature forms containing sialic acid in response to increased neuronal excitation. In exploring the basis of these N-glycosylation alterations, we discovered they result from the growth and proliferation of Golgi satellites scattered throughout the dendrite. Golgi satellites that formed with neuronal excitation were in close association with ER exit sites and early endosomes and contained glycosylation machinery without the Golgi structural protein, GM130. They functioned as distal glycosylation stations in dendrites, terminally modifying sugars either on newly synthesized glycoproteins passing through the secretory pathway, or on surface glycoproteins taken up from the endocytic pathway. These activities led to major changes in the dendritic surface of excited neurons, impacting binding and uptake of lectins, as well as causing functional changes in neurotransmitter receptors such as nicotinic acetylcholine receptors. Neural activity thus boosts the activity of the dendrites satellite micro-secretory system by redistributing Golgi enzymes involved in glycan modifications into peripheral Golgi satellites. This remodeling of the neuronal surface has potential significance for synaptic plasticity, addiction and disease.

neuroscience↗

bioRxiv2020

The Abelson tyrosine kinase and the Nedd4-family ubiquitin ligase Suppressor of Deltex converge at the Notch PPxY motif to regulate endosomal trafficking and signaling

The conserved Notch signaling pathway coordinates diverse cellular processes during animal development. Unlike most cell surface receptors that use a cytoplasmic cascade to amplify and diversify signaling dynamics, Notch itself transduces external cues directly to the nucleus. How appropriate signaling dynamics and transcriptional responses are achieved with this pathway architecture remains unclear. Here, we report that the cytoplasmic tyrosine kinase Abelson (Abl) fine-tunes Notch signaling by regulating Notch endocytic trafficking. We show that Abl can directly phosphorylate a PPxY motif important for Nedd4-family ubiquitin-ligase-mediated transfer of Notch into degradative endosomal compartments. Consistent with this, loss of Abl or inhibition of its kinase activity results in aberrant endosomal accumulation of Notch, while mutation of the PPxY tyrosine renders Notch insensitive to such regulation. Phenotypic and genetic interaction studies in the wing, together with parallel assays in cultured cells, show that loss or gain of Abl activity can respectively increase or decrease Notch output. We propose that the Notch PPxY motif operates as a molecular hub that integrates multiple post-translational modifications to regulate Notch trafficking and fine-tune signaling output.

developmental biology↗

bioRxiv2020

ESCargo: a regulatable fluorescent secretory cargo for diverse model organisms

Membrane traffic can be studied by imaging a cargo protein as it transits the secretory pathway. The best tools for this purpose initially block exit of the secretory cargo from the endoplasmic reticulum (ER), and then release the block to generate a cargo wave. However, previously developed regulatable secretory cargoes are often tricky to use or specific for a single model organism. To overcome these hurdles for budding yeast, we recently optimized an artificial fluorescent secretory protein that exits the ER with the aid of the Erv29 cargo receptor, which is homologous to mammalian Surf4. The fluorescent secretory protein forms aggregates in the ER lumen and can be rapidly disaggregated by addition of a ligand to generate a nearly synchronized cargo wave. Here we term this regulatable secretory protein ESCargo (Erv29/Surf4-dependent Secretory Cargo) and demonstrate its utility not only in yeast cells, but also in cultured mammalian cells, Drosophila cells, and the ciliate Tetrahymena thermophila. Kinetic studies indicate that rapid transport out of the ER requires recognition by Erv29/Surf4. By choosing an appropriate ER signal sequence and expression vector, this simple technology can likely be used with many model organisms.

cell biology↗