The Retinal Ganglion Cell Transportome Identifies Proteins Transported to Axons and Presynaptic Compartments in the Visual System In Vivo

Summary: The brain processes information and generates cognitive and motor outputs through functions of spatially organized proteins in different types of neurons. More complete knowledge of proteins and their distributions within neuronal compartments in intact circuits would help in the understanding of brain function. We used unbiased in vivo protein labeling with intravitreal NHS-biotin for discovery and analysis of endogenous axonally transported proteins in the visual system using tandem mass spectrometric proteomics, biochemistry, and both light and electron microscopy. Purification and proteomic analysis of biotinylated peptides identified ∼1,000 proteins transported from retinal ganglion cells into the optic nerve and ∼575 biotinylated proteins recovered from presynaptic compartments of lateral geniculate nucleus and superior colliculus. Approximately 360 biotinylated proteins were differentially detected in the two retinal targets. This study characterizes axonally transported proteins in the healthy adult visual system by analyzing proteomes from multiple compartments of retinal ganglion cell projections in the intact brain. : Axonal protein transport is essential for circuit function. Schiapparelli et al. use unbiased in vivo protein labeling and mass spectrometry to identify ∼1,000 proteins in the “RGC axonal transportome.” About 350 retinal proteins are differentially transported to the lateral geniculate nucleus or the superior colliculus, indicating target-specific diversity in presynaptic protein content. Keywords: NHS-biotin, DiDBiT, axon transport, proteomics, protein labeling, optic nerve, superior colliculus, lateral geniculate nucleus, retinal ganglion cell, electron microscopy