Biology subjects

Narayanan, V.

Publications and source records attributed to Narayanan, V..

7 recordsLinked to original sources

bioRxiv2025

Multiciliated cells adapt the mechanochemical Piezo1-Erk1/2-Yap1 cell proliferation axis to fine-tune centriole number.

Multiciliated cells (MCCs) are specialized epithelial cells that undergo massive amplification of centrioles, constructing several motile cilia to propel fluid flow. The abundance of cilia is critical for efficient fluid flow, yet how MCCs regulate centriole/cilia numbers remains a major knowledge gap. We have shown that mechanical tension plays a central role in regulating apical area and centriole number in MCCs. Here, we demonstrate that centriole amplification is controlled by a mechanochemical pathway essential for cell proliferation in cycling cells. Specifically, MCCs under tension use Piezo1-mediated calcium signaling to drive Erk[1/2] phosphorylation via PKC and subsequent Yap1 activation. Remarkably, MCCs use this pathway to activate a cilia-specific transcription program, influencing the expression of Foxj1, a master regulator of motile ciliogenesis. Our work is the first to identify a novel function for an important mechanochemical pathway in centriole amplification in MCCs, offering new insights into ciliopathies and cancer, where aberrant centriole numbers are implicated. TeaserThis study demonstrates that multiciliated cells utilize the mechanochemical Piezo1-Erk1/2-Yap1 cell proliferation axis to activate the cilia-specific transcriptional factor Foxj1 and amplify centrioles in a tension- dependent manner.

cell biology↗

bioRxiv2024

Characterizing CSNK2A1 Mutant-Induced Morphological Phenotypes in Zebrafish (Danio rerio): Insights into Okur-Chung Neurodevelopmental Syndrome (OCNDS)

Okur-Chung Neurodevelopmental Syndrome (OCNDS) is a rare, autosomal dominant disorder caused by heterozygous pathogenic variants in the CSNK2A1 gene. CSNK2A1 encodes the subunit of protein kinase CK2, involved in diverse biological processes. In 2016, Okur et al. reported the discovery of germline de novo missense and canonical splice site mutations in CSNK2A1 in five female patients with OCNDS. The syndrome is characterized by developmental delays, intellectual disability, hypotonia, feeding difficulties, dysmorphic facial features, and disrupted circadian rhythms, leading to sleep disturbances. The complex phenotypic spectrum of OCNDS underscores the need for robust model systems to investigate genotype-phenotype correlations, disease mechanisms, and potential therapies. In this study, we employed an overexpression strategy in a zebrafish model to investigate the functional consequences of select CSNK2A1 variants implicated in OCNDS. Our findings revealed distinct morphological phenotypes resulting from the overexpression of different CSNK2A1 mutants, indicating a direct correlation between genetic alterations and phenotypic manifestations. Notably, the CSNK2A1 p.Arg191Ter (R191X) mutation had a significant impact on the phenotype. Co-injection of wild-type CSNK2A1 mRNA with mutant CSNK2A1 mRNA rescued morphological abnormalities in zebrafish embryos. Overall our study highlights the utility of zebrafish as an adaptable model system for examining the functional impact of CSNK2A1 mutations and exploring novel therapeutic avenues.

neuroscience↗

bioRxiv2022

Loss of mechanical homeostasis drives epithelial acinar eversion

Epithelial cells lining a gland and cells grown in a soft extracellular matrix polarize with apical proteins exposed to the lumen and basal proteins in contact with the extracellular matrix. Alterations to polarity, including an apical-out polarity, occur in human cancers. While some aberrant polarity states may result from altered protein trafficking, recent observations of an extraordinary tissue-level inside-out unfolding suggest an alternate pathway for altered polarity. Because mechanical alterations are common in human cancer including an upregulation of RhoA mediated actomyosin tension in acinar epithelia, we explored whether perturbing mechanical homeostasis could cause apical-out eversion. Acinar eversion was robustly induced by direct activation of RhoA in normal and tumor epithelial acini, or indirect activation of RhoA through blockage of {beta}1 integrins, disruption of the LINC complex, oncogenic Ras activation, or Rac1 inhibition. Furthermore, laser ablation of a portion of the untreated acinus was sufficient to induce eversion. Analyses of acini revealed high curvature and low phosphorylated myosin in the apical cell surfaces relative to the basal surfaces. A vertex-based mathematical model which balances tension at cell-cell interfaces revealed a five-fold greater basal cell surface tension relative to the apical cell surface tension. The model suggests that the difference in surface energy between the apical and basal surfaces is the driving force for acinar eversion. Our findings raise the possibility that a loss of mechanical homeostasis may cause apical-out polarity states in human cancers.

biophysics↗

bioRxiv2021

A myosin chaperone, UNC-45A, is a novel regulator of intestinal epithelial barrier integrity and repair

The actomyosin cytoskeleton serves as a key regulator of the integrity and remodeling of epithelial barriers by controlling assembly and functions of intercellular junctions and cell-matrix adhesions. While biochemical mechanisms that regulate activity of non-muscle myosin II (NM-II) in epithelial cells have been extensively investigated, little is known about assembly of the contractile myosin structures at the epithelial adhesion sites. UNC-45A is a cytoskeletal chaperone that is essential for proper folding of NM II heavy chains and myofilament assembly. We found abundant expression of UNC-45A in human intestinal epithelial cell (IEC) lines and in the epithelial layer of the normal human colon. Interestingly, protein levels of UNC-45A were decreased in colonic epithelium of patients with ulcerative colitis. CRISPR/Cas9-mediated knock-out of UNC-45A in HT-29 and SK-CO15 IEC disrupted epithelial barrier integrity, impaired assembly of epithelial adherence and tight junctions and attenuated cell migration. Consistently, decreased UNC-45 expression increased permeability of the Drosophila gut in vivo. The mechanisms underlying barrier disruptive and anti-migratory effects of UNC-45A depletion involved disorganization of the actomyosin bundles at epithelial junctions and the migrating cell edge. Loss of UNC-45A also decreased contractile forces at epithelial junctions and matrix adhesions. Expression of deletion mutants revealed roles for the myosin binding domain of UNC-45A in controlling IEC junctions and motility. Our findings uncover a novel mechanism that regulates integrity and restitution of the intestinal epithelial barrier, which may be impaired during mucosal inflammation.

cell biology↗

bioRxiv2021

Pathological LSD1 mutations cause HDAC-mediated aberrant gene repression during early cell differentiation

Lysine-specific demethylase 1 (LSD1/KDM1A) demethylates both histone and non-histone substrates, recruits repressive chromatin complexes, and is increased in cancers. De novo LSD1 mutations impairing protein function lead to a rare developmental disorder, but the molecular details of the pathology remains unclear. Using patient-derived fibroblasts, reprogrammed pluripotent stem cells, and differentiated cells, we found over 4000 differentially expressed genes and 68 transcription factors (TFs) whose motif accessibilities changed upon LSD1 mutation. An enhancer-mediated gene regulatory network approach identified transcriptional repressors with impaired activity in fibroblast and stem cells, leading to erroneous activation of their target genes. We also revealed overall decreases in TF target gene expression during early lineage differentiation of LSD1 mutant stem cells, likely caused by increased activity of repressive histone deacetylases (HDACs), co-factors of LSD1. Indeed, an HDACs inhibitor restored changes in gene expression including downregulation phenotype. Our findings characterize the molecular pathogenesis of LSD1 mutations and suggest potential therapeutic strategies for the developmental disorder and cancers caused by LSD1 dysregulations.

genomics↗

bioRxiv2020

Complex genetic network underlying the convergent of Rett Syndrome like (RTT-L) phenotype in neurodevelopmental disorders

Mutations of the X-linked gene encoding methyl-CpG-binding protein 2 (MECP2) cause classical forms of Rett syndrome (RTT) in girls. Patients with features of classical Rett syndrome, but do not fulfill all the diagnostic criteria (e.g. absence of a MECP2 mutation), are defined as atypical Rett syndrome. Genes encoding for cyclin-dependent kinase-like 5 (CDKL5) and forkhead box G1 (FOXG1) are more commonly found in patients with atypical Rett syndrome. Nevertheless, a subset of patients who are recognized to have an overlapping phenotype with RTT but are lacking a mutation in a gene that causes typical or atypical RTT are described as having Rett syndrome like phenotype (RTT-L). Whole Exome Sequencing (WES) of 8 RTT-L patients from our cohort revealed mutations in the genes GABRG2, GRIN1, ATP1A2, KCNQ2, KCNB1, TCF4, SEMA6B, and GRIN2A, which are seemingly unrelated to Rett syndrome genes. We hypothesized that the phenotypic overlap in RTT and RTT-L is caused by mutations in genes that affect common cellular pathways critical for normal brain development and function. We annotated the list of genes identified causing RTT-L from peer-reviewed articles and performed a protein-protein interaction (PPI) network analysis. We also investigated their interaction with RTT (typical or atypical) genes such as MECP2, CDKL5, NTNG1, and FOXG1. We found that the RTT-L-causing genes were enriched in the biological pathways such as circadian entrainment, the CREB pathway, and RET signaling, and neuronal processes like ion transport, synaptic transmission, and transcription. We conclude that genes that significantly interact with the PPI network established by RTT genes cause RTT-L, explaining the considerable feature overlap between genes that are indicated for RTT-L and RTT.

genomics↗

bioRxiv2019

A Predictive Model of Intercellular Tension and Cell-Matrix Mechanical Interactions in a Multicellular Geometry

Epithelial cells form continuous sheets of cells that exist in tensional homeostasis. Homeostasis is maintained through cell-to-cell adhesions that distribute tension and balance forces between cells and their underlying matrix. Disruption of tensional homeostasis can lead to Epithelial-Mesenchymal Transition (EMT), which is a transdifferentiation process in which epithelial cells adopt a mesenchymal phenotype, where cell-cell adhesion is lost and individual cell migration is acquired. This process is critical during embryogenesis and wound healing, but is also dysregulated in many disease states. To further understand the role of intercellular tension in spatial patterning of epithelial cell monolayers, we developed a multicellular computational model of cell-cell and cell-substrate forces. This work builds on a hybrid Cellular Potts-finite element model to evaluate cell-matrix mechanical feedback of an adherent multicellular cluster. Thermodynamically-constrained cells migrate by generating traction forces on a finite element substrate to minimize the total energy of the system. Junctional forces at cell-cell contacts balance these traction forces, thereby producing a mechanically stable epithelial monolayer. Simulations were compared to in vitro experiments using fluorescence-based junction force sensors in clusters of cells undergoing EMT. Results indicate that the multicellular CPM model can reproduce many aspects of EMT, including epithelial monolayer formation dynamics, changes in cell geometry, and spatial patterning of cell geometry and cell-cell forces in an epithelial colony.\n\nAuthor summaryEpithelial cells line all organs of the human body and act as a protective barrier by forming a continuous sheet. These cells exert force on both their neighboring cells as well as the underlying extracellular matrix, which is a network of proteins that creates the structure of tissues. Here we develop a model that encompasses both cell-cell forces and cell-matrix forces in an epithelial cell sheet. The model accounts for cell migration and proliferation, and regulates how cell-cell adhesions are formed. We demonstrate how the interplay between cell-cell forces and cell-matrix forces can regulate the formation of the epithelial cell sheet, the organization of cells within the sheet, and the pattern of cell geometries and cell forces within the sheet. We compare computational results with experiments in which epithelial cell sheets are disrupted and cell-cell junction forces are measured, and demonstrate that the model captures many aspects of epithelial cell dynamics observed experimentally.

cell biology↗