Biology subjects

Selvin, P. R.

Publications and source records attributed to Selvin, P. R..

10 recordsLinked to original sources

bioRxiv2024

Nanoscale organization is changed in native, surface AMPARs by mouse brain region and tauopathy

The distribution of synaptic and extra-synaptic AMPA receptors (AMPARs) on neuronal plasma membranes is correlated with learning and memory. Although AMPAR organization has been extensively studied in neuronal cultures, its native cell-surface distribution in intact adult brain tissue across distinct brain regions and in neurodegenerative pathology remains poorly understood. Here, we combine a selective small-molecule labeling strategy with two-color 3D super-resolution dSTORM imaging to map native surface AMPAR organization at the nanoscale in 30 micron thick mouse brain slices. We find that wild-type mice exhibit marked regional differences in AMPAR organization, with the CA1 hippocampus containing a substantially larger extrasynaptic AMPAR pool than the nearby motor and somatosensory cortex. In the PS19 tauopathy mouse model, at an age preceding overt neurodegeneration, AMPAR organization is selectively disrupted in the hippocampus but largely preserved in the cortex. Specifically, we observe depletion of the extrasynaptic receptor pool together with reduced synaptic nanodomain organization, revealing early molecular-scale synaptic remodeling associated with tau pathology. These findings provide direct structural insight into region- and disease-dependent AMPAR organization in intact adult brain tissue and establish a broadly applicable framework for nanoscale investigation of synaptic receptor architecture in health and neurological disease.

neuroscience↗

bioRxiv2024

Automatic dendritic spine segmentation in widefield fluorescence images reveal synaptic nanostructures distribution with super-resolution imaging

Relating dendritic spine morphology to synaptic organization in brain tissue is essential for understanding excitatory synaptic transmission and plasticity. Single-molecule localization microscopy (SMLM) offers the spatial precision needed to study the synaptic protein distribution at the nanoscale. However, the widefield setup required for SMLM produces diffraction-limited images with poor contrast and resolution in thick brain slices (> 30 m), making accurate segmentation of dendritic spines challenging. To overcome this challenge, we developed an automated 3D segmentation approach tailored to this condition by combining two existing machine-learning models. We integrated this strategy with SMLM-based localization of synaptic proteins to map post-synaptic protein PSD-95 within spines at nanoscale resolution. This framework, named ISEPLA (Integrated Spine Extraction and Protein Localization Analysis), revealed a hierarchical organization of synaptic proteins: spines contain multiple nanomodules, each composed of smaller nanodomains. Larger spines contain more nanomodules, and larger nanomodules comprise more nanodomains. Therefore, our method enables precise morphological and molecular analysis under physiologically relevant imaging conditions, providing new insights into the synaptic organization in spines.

neuroscience↗

bioRxiv2024

Stepping dynamics of dynein characterized by MINFLUX

Cytoplasmic dynein is the principal motor for minus-end-directed motility and force generation functions along microtubules (MTs)1. Dynein converts the chemical energy of ATP hydrolysis into coordinated structural changes to step processively along MTs, but how dynein couples ATP hydrolysis to a minus-end-directed step remains controversial2, 3. The dynamics of dynein stepping have previously been characterized by tracking flexible regions of the motor with limited resolution4-6. Here, we site-specifically labeled yeast dynein at its MT-binding domain by developing a cysteine-light mutant and tracked its stepping at sub-millisecond and nanometer resolution at physiological ATP concentrations using MINFLUX7. We show that dynein hydrolyzes one ATP per step and takes multiples of 8 nm steps. Steps are preceded by a transient movement towards the plus end. These backward "dips" correspond to MT release upon ATP binding and subsequent diffusion of the stepping monomer around its MT-bound partner. Functional assays showed that dips terminate with a minus-end-directed movement upon ATP hydrolysis. These results provide critical insights into the order of mechanochemical events that result in a productive step of dynein.

biophysics↗

bioRxiv2023

Synapses without tension fail to fire in an in vitro network of hippocampal neurons.

Neurons in the brain communicate with each other at their synapses. It has long been understood that this communication occurs through biochemical processes. Here, we reveal a previously unrecognized paradigm wherein mechanical tension in neurons is essential for communication. Using in vitro rat hippocampal neurons, we find that (1) neurons become tout/tensed after forming synapses resulting in a contractile neural network, and (2) without this contractility, neurons fail to fire. To measure time evolution of network contractility in 3D (not 2D) extracellular matrix, we developed an ultra-sensitive force sensor with 1 nN resolution. We employed Multi-Electrode Array (MEA) and iGluSnFR, a glutamate sensor, to quantify neuronal firing at the network and at the single synapse scale, respectively. When neuron contractility is relaxed, both techniques show significantly reduced firing. Firing resumes when contractility is restored. Neural contractility may play a crucial role in memory, learning, cognition, and various neuropathologies.

neuroscience↗

bioRxiv2022

Peptide-PAINT using a transfected-docker enables live- and fixed-cell super-resolution imaging

Point accumulation for imaging in nanoscale topography (PAINT) is a single-molecule technique for super-resolution microscopy, achieving [~]5-25 nanometer resolution. Here we show that by transfecting the protein-of-interest with a docker-coil, rather than by adding the docker externally--as is the norm when using DNA tethers or antibodies as dockers--we can achieve similar localization, [~]10 nm. However, using a transfected docker has several experimental advances and simplifications. Most importantly, it allows Peptide-PAINT to be applied to transfected live cells, including surface proteins in mammalian cells and neurons under physiological conditions. The enhance resolution of Peptide-PAINT is also shown for organelles in fixed cells to unravel structural details including {approx}40-nm and {approx}60-nm axial repeats in vimentin filaments in the cytoplasm, and fiber shapes of sub-100-nm histone-rich regions in the nucleus.

biophysics↗

bioRxiv2021

Single molecule tracking of AMPA receptors shows the role of synaptic insertion during maintenance of chemical LTP

Long term potentiation (LTP) likely contributes to memory formation. Early expression of LTP involves insertion of AMPA receptors (AMPARs) to the extrasynaptic membrane followed by their lateral diffusion into the synaptic membrane. However, whether a similar mechanism mediates the maintenance of LTP is unclear. Using single-molecule microscopy, we quantified that 6 GluA1- and 11 GluA2-containing endogenous AMPARs were added per synapse in cultured hippocampal neurons at 20 min following chemical LTP (cLTP) induction for 10 min, resulting in a 54% increase for both subunits. Single molecular tracking of transfected subunits revealed that the number of exocytosed subunits at the synapse increased by 15-18% from 5 to 20 min following cLTP induction, but their lateral exchange between synaptic and extrasynaptic membranes was minimal. These findings suggest that cLTP maintenance is contributed largely by synaptic insertion of AMPARs rather than the surface diffusion of exocytosed AMPARs from extrasynaptic to synaptic regions.

biophysics↗

bioRxiv2021

Individual Molecular Motors use Low Forces to bypass Roadblocks during Collective Cargo Transport

A cargo encounters many obstacles during its transport by molecular motors as it moves throughout the cell. Multiple motors on the cargo exert forces to steer the cargo to its destination. Measuring these forces is essential for understanding intracellular transport. Using kinesin as an example, we measured the force exerted by multiple stationary kinesins in vitro, driving a common microtubule. We find that individual kinesins generally exert less than a piconewton (pN) of force, even while bypassing obstacles, whether these are artificially placed 20-100 nm particles or tau, a Microtubule Associated Protein. We demonstrate that when a kinesin encounters an obstacle, the kinesin either becomes dislodged and then re-engages or switches protofilaments while the other kinesins continue to apply their (sub-)pN forces. By designing a high-throughput assay involving nanometer-resolved multicolor-fluorescence and a force-sensor able to measure picoNewtons of force, our technique is expected to be generally useful for many different types of molecular motors.

biophysics↗

bioRxiv2019

Asymmetric Tug-of-War leads to Cooperative Transport of a Cargo by Multiple Kinesins

How cargoes move within a crowded cell--over long distances and at speeds that are nearly the same as when moving on an unimpeded pathway--has long been mysterious. Through an in vitro gliding assay, which involves measuring nanometer displacement and piconewtons of force, we have evidence that when kinesins, a cytoplasmic molecular motor, operate in small groups, from 2-10, they can communicate among themselves through an asymmetric tug-of-war by inducing tension (up to 4 pN) on the cargo. Surprisingly, the primary role of approximately one-third of kinesins is to develop tension, which instantaneously slows forward motion but helps increase cargo run length. These hindering kinesins fall off rapidly when experiencing a forward tug. Occasionally, they may be ripped off from their anchors by other driving kinesins working in tandem. Furthermore, with roadblocks on the microtubule, multiple kinesins cooperate to overcome impediments. Hence, kinesin may employ an asymmetric tug-of-war and a cooperative motion to navigate through cellular environment.

biophysics↗

bioRxiv2018

Photon-separation to enhance the spatial resolution in pulsed STED microscopy

Stimulated emission depletion microscopy (STED) is one of the pivotal super-resolution techniques. It overcomes the spatial resolution limit imposed by the diffraction by using an additional laser beam, the STED beam, whose intensity is directly related to the achievable resolution. Despite achieving nanometer resolution, much effort in recent years has been devoted to reduce the STED beam intensity because it may lead to photo-damaging effects. Exploring the temporal dynamics of the detected fluorescence photons and accessing the encoded spatial information has proven to be a powerful strategy, and has contributed to the separation by lifetime tuning (SPLIT) technique. The SPLIT technique uses the phasor analysis to efficiently distinguish photons emitted from the center and the periphery of the excitation spot. It thus improves the resolution without increasing the STED beam intensity. This method was proposed for architectures based on STED beam running in continuous wave (CW-STED microscopy). Here, we extend it to architectures based on pulsed STED beam (pSTED microscopy). We show, through simulated and experimental data, that the SPLIT-pSTED method reduces the detection volume of the pSTED microscope without significantly reducing the signal-to-noise ratio of the final image, thus effectively improving the resolution without increasing the STED beam intensity.

biophysics↗

bioRxiv2016

Super-resolution Imaging of Synaptic and Extra-synaptic Pools of AMPA Receptors with Different-sized Fluorescent Probes

Whether AMPA receptors (AMPARs) enter into neuronal synapses, by exocytosis from an internal pool, or by diffusion from an external membrane-bound pool, is hotly contested. 3D super-resolution fluorescent nanoscopy to measure the dynamics and placement of AMPAR is a powerful method for addressing this issue. However, probe size and accessibility to tightly packed spaces can be limiting. We have therefore labeled AMPARs with differently sized fluorophores: small organic fluorescent dyes (~ 4 nm), small quantum dots (sQD, ~10 nm in diameter), or big (commercial) quantum dots (bQD, ~ 20 nm in diameter). We then compared their diffusion rate, trajectories, and placement with respect to a postsynaptic density (PSD) protein, Homer 1c. Labeled with the small probes of sQDs or organic fluorophores, we find that AMPARs are located largely within PSDs (~73-93%), and generally reside in \"nanodomains\" with constrained diffusion. In contrast, when labeled with bQDs, only 5-10% of AMPARs are within PSDs. The results can be explained by relatively free access, or lack thereof, to synaptic clefts of the AMPARs when labeled with small or big probes, respectively. This implies that AMPARs primarily enter PSDs soon after their exocytosis and not from a large diffusive pool of extrasynaptic AMPARs.

neuroscience↗