Biology subjects

M'Saad, O.

Publications and source records attributed to M'Saad, O..

5 recordsLinked to original sources

bioRxiv2025

The Golgi Rim is a Precise Tetraplex of Golgin Proteins that Can Self-Assemble into Filamentous Bands

Golgin proteins have long been suspected to be organizers of the Golgi stack. Using three-dimensional super-resolution microscopy, we comprehensively localize the human golgin family at the rim of the Golgi apparatus at 10-20 nm resolution in situ. Unexpectedly, we find that the golgins are precisely organized into a tetraplex with four discrete layers, each containing a specific set of rim golgins. We observe no golgins inside the stack between its membrane-bound cisternae. Biochemically characterizing most of the golgins as isolated proteins, we find that they form anti-parallel dimers and further self-assemble into bands of multi-micron-long filaments. Based on our findings, we propose an "outside-in" physical model, the Golgin Organizer Hypothesis, in which the Golgi stack of cisternae and its overall ribbon morphology directly result from bending circumferential bands of rim golgin filaments onto a membrane surface, explaining stack formation without the need for special "stacking proteins."

cell biology↗

bioRxiv2022

Unclearing Microscopy

The spatial resolution and contrast sensitivity of the human eye is limited, restricting our ability to directly see subcellular structures. We report a new principle for unaided eye cellular visualization in a method we call Unclearing Microscopy. By expanding cells and tissue >8,000 volumetrically and opaquing their bulk with light-scattering molecules of sufficient density, cell microstructure can now be discerned with a contrast visible to the unaided eye. We further inspect uncleared samples with transmitted light microscopy modalities and prove that 3D ultrastructural features, previously accessible only with super-resolution fluorescence or electron microscopy methods, can now be visualized with simple magnification optics alone.

bioengineering↗

bioRxiv2022

All-optical visualization of specific molecules in the ultrastructural context of brain tissue

Understanding the molecular anatomy and neural connectivity of the brain requires imaging technologies that can map the 3D nanoscale distribution of specific proteins in the context of brain ultrastructure. Light and electron microscopy (EM) enable visualization of either specific labels or anatomical ultrastructure, but combining molecular specificity with anatomical context is challenging. Here, we present pan-Expansion Microscopy of tissue (pan-ExM-t), an all-optical mouse brain imaging method that combines [~]24-fold linear expansion of biological samples with fluorescent pan-staining of protein densities (providing EM-like ultrastructural context), and immunolabeling of protein targets (for molecular imaging). We demonstrate the versatility of this approach by imaging the established synaptic markers Homer1, Bassoon, PSD-95, Synaptophysin, the astrocytic protein GFAP, myelin basic protein (MBP), and anti-GFP antibodies in dissociated neuron cultures and mouse brain tissue sections. pan-ExM-t reveals these markers in the context of ultrastructural features such as pre and postsynaptic densities, 3D nanoarchitecture of neuropil, and the fine structures of cellular organelles. pan-ExM-t is adoptable in any neurobiological laboratory with access to a confocal microscope and has therefore broad applicability in the research community. HighlightsO_LIpan-ExM-t visualizes proteins in the context of synaptic ultrastructure C_LIO_LILipid labeling in pan-ExM-t reveals organellar and cellular membranes C_LIO_LIAll-optical, easily accessible alternative to correlative light/electron microscopy C_LIO_LIHigh potential for high throughput connectomics studies C_LI

neuroscience↗

bioRxiv2020

Light microscopy of proteins in their ultrastructural context

Resolving the distribution of specific proteins at the nanoscale in the structural context of the cell is a major challenge in fluorescence microscopy. Here we present a new concept that decrowds the intracellular space through 13 to 21-fold physical expansion while simultaneously retaining the proteins. This combination makes labeling of the proteome efficient enough that local protein densities are revealed and the cellular nanoarchitecture can be visualized by standard light microscopy.

cell biology↗

bioRxiv2019

3D super-resolution deep-tissue imaging in living mice

Stimulated emission depletion (STED) microscopy enables the three-dimensional (3D) visualization of dynamic nanoscale structures in living cells, offering unique insights into their organization. However, 3D-STED imaging deep inside biological tissue is obstructed by optical aberrations and light scattering. We present a STED system that overcomes these challenges. Through the combination of 2-photon excitation, adaptive optics, far-red emitting organic dyes, and a long-working distance water-immersion objective lens, our system achieves aberration-corrected 3D super-resolution imaging, which we demonstrate 164 {micro}m deep in fixed mouse brain tissue and 76 {micro}m deep in the brain of a living mouse.

biophysics↗