Biology subjects

Gadadhar, S.

Publications and source records attributed to Gadadhar, S..

6 recordsLinked to original sources

bioRxiv2026

Conformational activation of GSK3β by an environmental toxicant suppresses hedgehog signalling

Primary cilium-dependent hedgehog signalling is essential for embryonic development, tissue patterning, and organ homeostasis, and its dysfunction causes ciliopathies, a clinically diverse spectrum of developmental and reproductive disorders. Whether environmental chemicals can phenocopy genetic ciliopathies by directly targeting ciliary kinase machinery has remained unknown. Here we show that endosulfan, a banned organochlorine pesticide linked to congenital and reproductive defects, suppresses hedgehog signalling by driving proteolytic processing of GLI transcription factors into repressor forms. Excluding ciliary receptor trafficking, cAMP signalling, and GLI-DNA binding, we identify PKA and GSK3{beta} as direct endosulfan targets: endosulfan allosterically fine-tunes PKA activity and, to our knowledge, is the first reported small-molecule activator of GSK3{beta}, stabilising its active conformation, a profile distinct from all known inhibitors. We further identify Cetn3 and Cep250 as novel GLI-regulated genes required for centriole cohesion, both of which are repressed upon endosulfan exposure, linking this kinase axis to the reproductive defects reported in exposed human populations and animal models. These findings establish a chemical-biological axis through which an environmental toxicant hijacks core kinase signalling to phenocopy a genetic ciliopathy.

cell biology↗

bioRxiv2026

Endosulfan rewires PKA and GSK3β to disrupt primary cilia-dependent Hedgehog signalling

Primary cilium-dependent Hedgehog signalling is essential for embryonic development, tissue patterning, and organ homeostasis, and its disruption causes a spectrum of developmental disorders collectively termed ciliopathies. Whether environmental toxicants can chemically induce ciliopathy-like states by targeting this pathway, however, remains poorly understood. Here we show that endosulfan, a banned organochlorine pesticide epidemiologically linked to severe congenital and reproductive defects in exposed human populations, disrupts Hedgehog signalling by driving GLI transcription factor processing into repressor forms and suppressing target gene expression at both transcriptional and protein levels. Having excluded direct effects on core ciliary receptors and GLI-DNA binding, we identify the pathway kinases PKA and GSK3{beta} as direct targets of endosulfan: endosulfan increases PKA activity through allosteric fine-tuning, and -- in a pharmacologically rare finding -- acts as the first reported small-molecule activator of GSK3{beta}, shifting the kinase toward a catalytically active conformation. We further identify Cetn3 and Cep250 as novel GLI-regulated genes required for centriole cohesion, both of which are repressed upon endosulfan exposure, providing a mechanistic link to the reproductive defects reported in exposed populations and animal models. These findings identify endosulfan as a candidate chemical inducer of ciliopathy and reveal how an environmental toxicant can hijack core kinase signalling to disrupt Hedgehog-dependent development.

cell biology↗

bioRxiv2026

Glutamylated vimentin proteoform identified by a synthetic binder links to epithelial-mesenchymal plasticity

Cytoskeletal protein expression and filament dynamics change significantly during cell state transitions. However, post-translational modifications of cytoskeletal proteins during these transitions have rarely been described. Here, using a synthetic glutamylation-binder (SB2B49) selected against a bi-glutamylated peptide epitope, we identify a distinct pool of glutamylated vimentin filaments. We demonstrate that vimentin glutamylation is enzymatically added by tubulin tyrosine ligase-like (TTLLs) and removed by cytosolic carboxypeptidases (CCPs). Mass spectrometry and mutagenesis reveal that glutamylation occurs on specific vimentin residues. We find that glutamylated vimentin levels are dynamically modulated during epithelial-mesenchymal plasticity. During collective migration in scratch-wound assays, glutamylated vimentin filaments are transiently depleted at the wound edge, a process controlled by canonical glutamylation writer-erasers. Our findings reveal a new layer of vimentin regulation via glutamylation and establish the glutamylation-binder as a valuable tool for exploring the diversity of vimentin proteoforms and glutamylation modifications in both physiological and pathological contexts.

cell biology↗

bioRxiv2026

Tubulin glycylation regulates microtubule-protein interactions that are key for ciliary stability and trafficking

Tubulin glycylation, a cilia-specific posttranslational modification is emerging as a potentially key regulator of ciliary axonemal microtubules. However, insights into the functional consequences of glycylation have remained limited. Here, using in vitro reconstitution assays with unmodified or custom-glycylated tubulin, we provide a systematic mechanistic analysis of glycylation-dependent regulation of motors and microtubule-associated proteins. Our studies highlight that glycylation selectively enhances ciliary kinesin-2 motility while reducing kinesin-1 activity, suggesting a role in promoting efficient intraflagellar transport along axonemal microtubules. Moreover, glycylation protects microtubules from decay by suppressing the activities of the depolymerase MCAK and severing enzyme spastin, thereby enhancing stability. Notably, this regulation is dependent on the proportion of glycylation on the microtubule surface, coupled with concomitant reduction of glutamylation. Thus, by generating microtubule surfaces with distinct biochemical states, we establish that combinatorial modification patterns define functional microtubule properties especially in cilia. Together, our findings provide the first comprehensive mechanistic framework for tubulin glycylation in regulating molecular motors and MAPs in cilia, establishing glycylation as a key determinant of motor selectivity and microtubule stability within the axoneme.

biochemistry↗

bioRxiv2025

IntAct-U-ExM: Ultrastructure Expansion microscopy of actin networks via an internally-tagged actin

Expansion microscopy (ExM) has revolutionized super-resolution imaging in cell biology due to its simple and inexpensive workflow. The use of ExM has revealed several novel insights into the nanoscale architectures of cellular protein complexes, especially the microtubule cytoskeleton in model and non-model systems. Despite tremendous progress in expansion microscopy protocols that preserve cellular ultrastructure (U-ExM), compatible probes for imaging actin isoforms with U-ExM are still lacking and have hindered the study of diverse actin isoforms and networks across model systems. Here, we use IntAct, an internally tagged actin that incorporates into cellular actin networks, to develop and optimize U-ExM of diverse actin network types in both yeast and mammalian cells. Using expression of ALFA-tagged IntAct variants in yeast and mammalian cells, we show robust visualization of actin patches, cables, and rings in yeast and diverse actin networks such as actin cortex, stress fibers, filopodia, lamellipodium in mammalian cells at improved resolution. We also detect transient nuclear actin filaments using IntAct-U-ExM underscoring the advantages offered by our approach to image understudied actin structures. Overall, we demonstrate the effectiveness of IntAct-U-ExM for performing super-resolution imaging of various actin structures in an isoform-specific manner and highlight the potential of IntAct to study the nanoscale organization of diverse actin cytoskeletal networks across species. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=76 SRC="FIGDIR/small/654030v1_ufig1.gif" ALT="Figure 1"> View larger version (31K): org.highwire.dtl.DTLVardef@169cd82org.highwire.dtl.DTLVardef@1334af3org.highwire.dtl.DTLVardef@7d9d43org.highwire.dtl.DTLVardef@dfc50b_HPS_FORMAT_FIGEXP M_FIG C_FIG

cell biology↗

bioRxiv2024

Glutamylation imbalance leads to photoreceptor degeneration

The stereotypic structure of microtubules, assembled from conserved /{beta}-tubulin dimers is subject to a complex diversity of Post-translational Modifications (PTMs). PTMs are predicted to fine-tune microtubule properties and interactions with other proteins, thus allowing microtubules to perform specific functions. Cilia accumulate several types of tubulin PTMs, such as polyglutamylation, polyglycylation, detyrosination and acetylation, whose functions are not yet fully understood. Recently, mutations of AGBL5, coding for the deglutamylating enzyme CCP5, have been associated to retinitis pigmentosa, suggesting that perturbation of polyglutamylation leads to the degeneration of photoreceptor cells. However, the molecular mechanisms underlying this degeneration remain unknown. Here, using super-resolution Ultrastructure Expansion Microscopy in mouse and human photoreceptor cells, we found that most tubulin PTMs are accumulated at the level of the connecting cilium, a structure linking the outer and inner segments of photoreceptor cells. Using mouse models with increased glutamylation (Ccp5-/- and Ccp1-/-), or loss of tubulin acetylation (Atat1-/-), we demonstrated that aberrant glutamylation, but not loss of acetylation, resulted in perturbed molecular architecture of the outer segment, with the loss of the bulge region and destabilization of the distal axoneme. Concurrently, we observed a substantial impairment in tubulin glycylation and intraflagellar transport. Altogether our results indicate that glutamylation plays a crucial role in the maintenance of the molecular architecture of the outer segment and point to tubulin PTM imbalance as possible culprit in retinal degeneration.

cell biology↗