Pak, A. | bioRxiv Science

bioRxiv2020

A helical assembly of human ESCRT-I scaffolds reverse-topology membrane scission

The ESCRT complexes drive membrane scission in HIV-1 release, autophagosome closure, MVB biogenesis, cytokinesis, and other cell processes. ESCRT-I is the most upstream complex and bridges the system to HIV-1 Gag in virus release. The crystal structure of the headpiece of human ESCRT-I comprising TSG101:VPS28:VPS37B:MVB12A was determined, revealing an ESCRT-I helical assembly with a 12 molecule repeat. Electron microscopy confirmed that ESCRT-I subcomplexes form helical filaments in solution. Mutation of VPS28 helical interface residues blocks filament formation in vitro and autophagosome closure and HIV-1 release in human cells. Coarse grained simulations of ESCRT assembly at HIV-1 budding sites suggest that formation of a 12-membered ring of ESCRT-I molecules is a geometry-dependent checkpoint during late stages of Gag assembly and HIV-1 budding, and templates ESCRT-III assembly for membrane scission. These data show that ESCRT-I is not merely a bridging adaptor, but has an essential scaffolding and mechanical role in its own right.

biophysics↗

bioRxiv2020

Differential processing and habituation in distinct spatial frequency channels in V1 of a mouse model of fragile X syndrome

Extraction of both common and unique features across different visual inputs is crucial for animal survival. Regularities in the visual input lead to learning of the general principles governing an environment, whereas unique features are important for novelty detection. Low and high spatial frequencies (SF) represent two different channels of visual perception, which may be playing different roles in the processing of global pattern and local details. Alterations in the processing of these different SF channels may lead to impaired visual perception. Excessive detail-oriented processing and reduced habituation to sensory stimuli are some of the hallmarks of altered sensory perception in autism. However, the underlying neural mechanisms of these impairments are not understood. To gain insight into the pathophysiology of these impairments, we investigated the low and high SF channels in V1 of Fmr1 KO mice, the mouse model of Fragile X syndrome (FX). We first provide behavioral evidence for reduced habituation of both pupillary baseline and surprise responses in FX mice. Using silicon probe recordings, we demonstrate excessive processing of high SF stimuli in the late stages of visual responses in V1 of FX mice. We then show a reduced adaptation during a visual oddball paradigm in neurons preferring low but not high SF. Overall, our findings suggest that altered processing in distinct SF channels might contribute to altered visual perception and learning in FX and autism.

neuroscience↗