Biology subjects

Sabri, E.

Publications and source records attributed to Sabri, E..

6 recordsLinked to original sources

bioRxiv2026

Light-controlled membrane remodeling in gel-fluid phase-separated giant vesicles using photoswitchable lipids

Photoswitchable lipids enable optical control of membrane area, mechanics and phase behavior, offering a platform to study stimuli-responsive biomimetic systems. However, it remains unclear how the spatial organization of coexisting membrane phases governs photoinduced mechanical responses. Here, we incorporate the photoswitch azobenzene-phosphatidylcholine (azoPC) and dipalmitoyphosphatidylcholine (DPPC) into gel-fluid phase-separated giant unilamellar vesicles (GUVs) to probe how domain architecture controls light-driven deformation. We combine differential scanning calorimetry, temperature-controlled confocal microscopy, and a calibrated heating stage to quantify phase transitions and visualize domain dynamics. Dispersed domains produce global GUV crumpling upon UV-light-induced trans-to-cis isomerization of azoPC, whereas coarsened fluid domains locally confine deformation to budding regions of the GUVs; both responses are reversed by blue light. Temperature-controlled imaging reveals that the gel-fluid transition in GUVs is considerably broader than the calorimetric profile suggests, with coexisting phases detectable well above the calorimetry peak transition temperature. Well above the transition temperature, i.e. in the fully melted membrane, UV irradiation unexpectedly induces reversible nucleation of gel-like flower domains, consistent with an increased transition temperature in the cis azoPC state due to lipid packing incompatibility with DPPC. These results demonstrate that membrane domain architecture dictates the spatial distribution of photoinduced remodeling and that photoswitchable lipids can tune both membrane morphology and phase equilibria, enabling new strategies for stimuli-responsive synthetic cells and soft actuators.

biophysics↗

bioRxiv2025

Label-free in situ approach for characterizing the macromolecular composition and water content in biomolecular condensates

Biomolecular condensates are membraneless cellular organelles that form via liquid-liquid phase separation of proteins and nucleic acids. Their functional roles are tightly coupled to material properties like viscosity and hydrophobicity, which serve as key markers of cellular state. However, conventional determination of condensate composition and water content relies on invasive procedures that can damage samples. Here, we introduce Raman spectroscopy coupled with spectral phasor analysis as an in situ, label-free approach to resolve the chemical profiles and molecular concentrations within both the dense and dilute phases of biomolecular condensates. This method outperforms traditional regression and deconvolution approaches, yielding a precise readout of client molecule partitioning. By accounting for contributions of the protein backbone to the Raman spectra of condensates, we assess the signature of "solid-like" hydrogen-bonded water from protein hydration, revealing that most water molecules within condensates retain bulk, "liquid-like" properties. Finally, using environment-sensitive fluorescent probes, we demonstrate that macromolecular structure and water content--rather than hydrogen bonding alone--drive condensate hydrophobicity; notably, the dense phase remains predominantly water-rich even at low apparent dielectric constants.

biophysics↗

bioRxiv2025

Fluorescence-based mapping of dielectric permittivity of condensates and their environment

Biomolecular condensates, essential for cellular organization, possess mesoscale properties largely governed by hydrophobicity, influencing molecule partitioning and material characteristics like viscosity, surface tension, and hydration. While hydrophobicitys role is increasingly recognized, its impact on membrane-condensate interactions remains unexplored. Here, we introduce a novel approach, combining hyperspectral imaging of an environment-sensitive dye and phasor analysis, to quantitatively map the local dielectric permittivity of both condensates and their environment with pixel resolution as sensed by the dye. This robust method reveals a surprisingly broad range of condensate permittivities, from oil-like to water-like. Importantly, we uncover that membrane affinity is not dictated by condensate permittivity itself, but by the permittivity contrast with their surroundings. Indeed, membrane wetting affinity is found to scale linearly with this contrast, unveiling a unifying dielectric principle governing condensate-membrane interactions. Compatible with live-cell and in vitro imaging, this technique provides unprecedented insights into condensate biophysics and function and opens new avenues for studying biomolecular condensate biology.

biophysics↗

bioRxiv2024

Developmental disruption of Mef2c in Medial Ganglionic Eminence-derived cortical inhibitory interneurons impairs cellular and circuit function

MEF2C is strongly linked to various neurodevelopmental disorders (NDDs) including autism, intellectual disability, schizophrenia, and attention-deficit/hyperactivity. Mice constitutively lacking one copy of Mef2c, or selectively lacking both copies of Mef2c in cortical excitatory neurons, display a variety of behavioral phenotypes associated with NDDs. The MEF2C protein is a transcription factor necessary for cellular development and synaptic modulation of excitatory neurons. MEF2C is also expressed in a subset of cortical GABAergic inhibitory neurons, but its function in those cell types remains largely unknown. Using conditional deletions of the Mef2c gene in mice, we investigated the role of MEF2C in Parvalbumin-expressing Interneurons (PV-INs), the largest subpopulation of cortical GABAergic cells, at two developmental timepoints. We performed slice electrophysiology, in vivo recordings, and behavior assays to test how embryonic and late postnatal loss of MEF2C from GABAergic interneurons impacts their survival and maturation, and alters brain function and behavior. We found that loss of MEF2C from PV-INs during embryonic, but not late postnatal, development resulted in reduced PV-IN number and failure of PV-INs to molecularly and synaptically mature. In association with these deficits, early loss of MEF2C in GABAergic interneurons lead to abnormal cortical network activity, hyperactive and stereotypic behavior, and impaired cognitive and social behavior. Our findings indicate that MEF2C expression is critical for the development of cortical GABAergic interneurons, particularly PV-INs. Embryonic loss of function of MEF2C mediates dysfunction of GABAergic interneurons, leading to altered in vivo patterns of cortical activity and behavioral phenotypes associated with neurodevelopmental disorders.

neuroscience↗

bioRxiv2023

Isolating Single Cycles of Neural Oscillations in Spiking Activity

Neural oscillations are prominent features of brain activity, observable through frequency-specific power changes in electroencephalograms (EEG) and local field potentials (LFP). They also manifest as rhythmic coherence across brain regions. Although the identification of oscillations has primarily relied on EEG and LFP, the intrinsic relation between neural oscillations and neuronal spiking is noteworthy. We investigate the potential to detect individual cycles of neural rhythms solely through the spiking activity of neurons, leveraging recent advances in densely recording large populations of neurons within a local network. The numerous spikes from many neurons within a local network estimate the networks activity over time, enabling the identification of cyclic patterns. Here, we utilize a Long Short Term Memory (LSTM) network to effectively isolate and align individual cycles of neural oscillations from the spiking of a densely recorded population of neurons. We applied this network to robustly isolate specific cycles in different brain regions of mice across different time scales, from gamma to ultra-slow rhythms spanning durations of up to hundreds of seconds. These ultra-slow rhythms, which are usually cut off in the LFP, are also detected in behavioral measures of arousal, such as pupil size and mouse facial motion, and show delayed coherence with corresponding rhythms in the population spiking. We used the isolated neural cycles to investigate two questions: 1) With isolated gamma cycles driven by sensory input, we achieved a more precise alignment of the trials in sensory stimulation experiments in the primary visual cortex (V1) of mice. This alignment compensates for the biological variation in the transmission times of sensory signals from the retina to V1 across trials. As a result, we retrieve more accurate neural dynamics in response to sensory stimulation. 2) We used the distinct cycles in population spiking of simultaneously recorded regions to measure the correlated spiking across brain regions separately on different time scales. We observed that the delay in population spiking between brain regions varies according to brain regions and different time scales.

neuroscience↗

bioRxiv2019

Viral manipulation of functionally distinct neurons from mice to humans

Recent success in identifying gene regulatory elements in the context of recombinant adeno-associated virus vectors have enabled cell type-restricted gene expression. However, within the cerebral cortex these tools are presently limited to broad classes of neurons. To overcome this limitation, we developed a strategy that led to the identification of multiple novel enhancers to target functionally distinct neuronal subtypes. By investigating the regulatory landscape of the disease gene Scn1a, we identified enhancers that target the breadth of its expression, including two that are selective for parvalbumin and vasoactive intestinal peptide cortical interneurons. Demonstrating the functional utility of these elements, we found that the PV-specific enhancer allowed for the selective targeting and manipulation of these neurons across species, from mice to humans. Finally, we demonstrate that our selection method is generalizable to other genes and characterize four additional PV-specific enhancers with exquisite specificity for distinct regions of the brain. Altogether, these viral tools can be used for cell-type specific circuit manipulation and hold considerable promise for use in therapeutic interventions.

neuroscience↗