Biology subjects

Shahid, F.

Publications and source records attributed to Shahid, F..

6 recordsLinked to original sources

bioRxiv2026

Circuit regulation along an activity continuum shapes flexible and stable representations during learning

Learning requires neural representations to flexibly incorporate new information while progressively stabilizing to support enduring memories. How neural circuits balance these demands remains unclear. Here, we identify complementary mechanisms supporting representational flexibility and stability in the medial entorhinal cortex (MEC), a key component of the cognitive map for memory-guided navigation. Longitudinal calcium imaging in mice learning novel virtual environments revealed a persistent axis of excitatory neuronal activity associated with distinct representational dynamics. Low-activity neurons exhibited intermittent activation that varied with learning stages and greater learning-dependent representational refinement, flexibly shifting their encoding from landmarks toward reward locations. By contrast, high-activity neurons exhibited more persistent activation and maintained more stable spatial representations. Dopaminergic pre-reward ramping was associated with the emergence of reward encoding in low-activity neurons, whereas interactions with inhibitory interneurons contributed to the stability of high-activity neurons. Notably, interneurons exhibited activity changes opposing those of excitatory neurons during learning, and their transient activation upon novelty exposure delayed excitatory representational remodeling, stabilization, and behavioral learning, suggesting that inhibitory circuits gate learning-dependent representational dynamics. Together, these findings reveal how activity-dependent excitatory neuronal organization and circuit-level regulation enable complementary forms of representational flexibility and stability to coexist, facilitating the incorporation of novel experiences into stable, context-specific cognitive maps that support learning.

neuroscience↗

bioRxiv2025

Slow synaptic plasticity from the hippocampus underlies gradual mapping and fragmentation of novel spaces by grid cells

Animals construct internal "cognitive maps" of the world during navigation in spatial and non-spatial domains, with grid cells in the medial entorhinal cortex (MEC) playing a key role. This requires associating internal position estimates with external cues to reduce spatial uncertainty over time. However, how grid cell representations evolve in novel spaces to support map formation is unclear. To address this question, we longitudinally imaged calcium dynamics of grid cells over 10 days as mice learn operant tasks in novel virtual linear tracks. We observe that spatial tuning of grid cells is present immediately in novel tracks but evolves as a significant fraction of spatial fields shift backward on a run-by-run basis, within and across days. Backward shifts are more prevalent and persistent in successful learners. The fields gradually stabilize across days, anchored by landmarks, suggesting slow plasticity. The backward shifts partially reset daily, reflecting a slower consolidation timescale. While individual fields of a cell shift differentially, co-active fields of co-modular grid cells shift together, indicating their coupled dynamics on the same two-dimensional torus. Spatial learning leads to systematic changes and stabilization of their population phase trajectory, including lateral shift, rotation, and phase resets at landmarks, forming a landmark-fragmented representation for the environment. Next, we build an entorhinal-hippocampal model that provides a mechanistic explanation of the diverse phenomena - grid field shifts, increasing fidelity, and fragmentation of the spatial map - and predicts slow Hebbian plasticity in the hippocampus-to-entorhinal pathway. Supporting this, electrophysiology demonstrates that learning-performance-correlated weakening of local inhibition facilitates potentiation of indirect hippocampal inputs to superficial MEC. Together, our study provides multifaceted evidence of slow hippocampus-to-MEC plasticity, elucidating the formation of stable and fragmented cognitive maps that combine internal and cue-driven positional estimates in rich environments during learning. This mechanism may extend to broader memory processes involving this circuit.

neuroscience↗

bioRxiv2025

The entorhinal spatial map integrates visual identity information of landmarks

The location and identity of landmarks provide spatial and nonspatial information of an environment, respectively, to guide spatial navigation. While the medial entorhinal cortex (MEC) is essential for representing spatial information, it is unclear whether it also encodes landmark identity. Here, we conducted two-photon calcium imaging of the MEC when mice navigated in multiple virtual environments, and discovered a general ability of the MEC to encode landmark identity through cue cells, which responded to individual landmarks during virtual navigation. Cue cells represented landmark identity by exhibiting more distinct activity patterns between visually disparate landmarks than identical ones. The representation was modulated by the spatial shift of cue cell activity relative to landmark location. Moreover, the identity encoding by the same cue cell population changed between different environments but was maintained within the same environment despite increased experience. In contrast, landmark location encoding by cue cells was regulated by experience, suggesting different mechanisms underlying the encodings of landmark identity and location. Finally, compared to cue cells, grid cells weakly encoded landmark identity but more robustly encoded landmark location. Thus, the MEC integrates both spatial and nonspatial information during navigation, but potentially through different circuit mechanisms.

neuroscience↗

bioRxiv2025

Therapeutic Potential of PRMT1 as a Critical Survival Dependency Target in Multiple Myeloma

Multiple myeloma (MM) is a neoplasm of antibody-producing plasma cells and is the second most prevalent hematological malignancy worldwide. Development of drug resistance and disease relapse significantly impede the success of MM treatment, highlighting the critical need to discover novel therapeutic targets. In a custom CRISPR/Cas9 screen targeting 197 DNA damage response-related genes, Protein Arginine N-Methyltransferase 1 (PRMT1) emerged as a top hit, revealing it as a potential therapeutic vulnerability and survival dependency in MM cells. PRMT1, a major Type I PRMT enzyme, catalyzes the asymmetric transfer of methyl groups to arginine residues, influencing gene transcription and protein function through post-translational modification. Dysregulation or overexpression of PRMT1 has been observed in various malignancies including MM and is linked to chemoresistance. Treatment with the Type I PRMT inhibitor GSK3368715 resulted in a dose-dependent reduction in cell survival across a panel of MM cell lines. This was accompanied by reduced levels of asymmetric dimethylation of arginine (ADMA) and increased arginine monomethylation (MMA) in MM cells. Cell cycle analysis revealed an accumulation of cells in the G0/G1 phase and a reduction in the S phase upon GSK3368715 treatment. Additionally, PRMT1 inhibition led to a significant downregulation of genes involved in cell proliferation, DNA replication, and DNA damage response (DDR), likely inducing genomic instability and impairing tumor growth. This was supported by Reverse Phase Protein Array (RPPA) analyses, which revealed a significant reduction in levels of proteins associated with cell cycle regulation and DDR pathways. Overall, our findings indicate that MM cells critically depend on PRMT1 for survival, highlighting the therapeutic potential of PRMT1 inhibition in treating MM.

cancer biology↗

bioRxiv2024

Optogenetically Induced Microtubule Acetylation Unveils the Molecular Dynamics of Actin-Microtubule Crosstalk in Directed Cell Migration

Microtubule acetylation is implicated in regulating cell motility, yet its physiological role in directional migration and the underlying molecular mechanisms have remained unclear. This knowledge gap has persisted primarily due to a lack of tools capable of rapidly manipulating microtubule acetylation in actively migrating cells. To overcome this limitation and elucidate the causal relationship between microtubule acetylation and cell migration, we developed a novel optogenetic actuator, optoTAT, which enables precise and rapid induction of microtubule acetylation within minutes in live cells. Using optoTAT, we observed striking and rapid responses at both molecular and cellular level. First, microtubule acetylation triggers release of the RhoA activator GEF-H1 from sequestration on microtubules. This release subsequently enhances actomyosin contractility and drives focal adhesion maturation. These subcellular processes collectively promote sustained directional cell migration. Our findings position GEF-H1 as a critical molecular responder to microtubule acetylation in the regulation of directed cell migration, revealing a dynamic crosstalk between the actin and microtubule cytoskeletal networks.

cell biology↗

bioRxiv2020

Designing of a next generation multiepitope based vaccine (MEV) against SARS-COV-2: Immunoinformatics and in silico approaches

Coronavirus disease 2019 (COVID-19) associated pneumonia caused by severe acute respiratory coronavirus 2 (SARS-COV-2) was first reported in Wuhan, China in December 2019. Till date, no vaccine or completely effective drug is available to cure COVID-19. Therefore, an effective vaccine against SARS-COV-2 is crucially needed. This study was conducted to design an effective multiepitope based vaccine (MEV) against SARS-COV-2. Seven antigenic proteins were taken as targets and different epitopes (B-cell, T-cell and IFN-{gamma} inducing) were predicted. Highly antigenic and overlapping epitopes were shortlisted. Selected epitopes indicated significant interactions with the HLA-binding alleles and 99.29% coverage of the worlds population. Finally, 505 amino acids long MEV was designed by connecting sixteen MHC class I and eleven MHC class II epitopes with suitable linkers and adjuvant. Linkers and adjuvant were added to enhance the immunogenicity response of the MEV. The antigenicity, allergenicity, physiochemical properties and structural details of MEV were analyzed in order to ensure safety and immunogenicity. MEV construct was non-allergenic, antigenic, stable and flexible. Molecular docking followed by molecular dynamics (MD) simulation analysis, demonstrated a stable and strong binding affinity of MEV with human pathogenic toll-like receptors (TLR), TLR3 and TLR8. Codon optimization and in silico cloning of MEV ensured increased expression in the Escherichia coli K-12 system. Designed MEV in present study could be a potential candidate for further vaccine production process against COVID-19. However, to ensure its safety and immunogenic profile, the proposed MEV needs to be experimentally validated.

immunology↗