Biology subjects

Shin, J.-B.

Publications and source records attributed to Shin, J.-B..

13 recordsLinked to original sources

bioRxiv2026

Sperm development requires TMC5-dependent mechanoresponsive calcium entry

Spermiogenesis, the transformation of round spermatids into streamlined, fertilization-competent sperm, represents cellular morphogenesis at its most extreme. Despite decades of effort, spermiogenesis remains difficult to recapitulate outside the testis, highlighting the importance of cues within the native tissue environment. The nature of these cues, however, remains poorly understood. Here, we discover that mechanical stimulation elicits Ca2+ entry in spermatids and identify transmembrane channel-like protein 5 (TMC5) as a principal mediator of this response. In both mouse and human testes, TMC5 is selectively expressed in spermatids and localized to the plasma membrane. TMC5 associates with TMC7 and calcium- and integrin-binding (CIB) proteins, mirroring TMC-CIB mechanotransduction complexes in sensory organs. Mechanistically, loss of Tmc5 blocks mechanically evoked Ca2+ entry, leading to disruptions in cytoskeletal remodeling and failure of CREM [&tau] dependent transcriptional programs required for spermiogenesis. Thus, TMC5 is required to couple mechanical cues to sperm development, with direct implications for male infertility.

cell biology↗

bioRxiv2026

ATP8B1-TMEM30B Flippase Activity Maintains Stereocilia Lipid Asymmetry Required for Hearing

Sensory hair cells convert sound-induced vibrations into electrical signals through a process called mechano-electrical transduction (MET). While the protein components of the MET complex are well studied, increasing evidence indicates that MET channel properties are significantly modulated by the surrounding lipid bilayer. The asymmetric distribution of membrane lipids between the inner and outer membrane leaflets is well established to shape membrane mechanics. The recent discovery that the core MET components TMC1 and TMC2 also act as lipid scramblases suggests a direct role for membrane lipid asymmetry in the dynamic shaping of auditory transduction. Because scramblase activity of TMC1/2 disrupts lipid asymmetry, we hypothesized that an opposing flippase may be required to restore and maintain lipid asymmetry. Here, we identify the P4-ATPase ATP8B1 and its chaperone TMEM30B as selectively expressed in outer hair cells (OHCs), enriched in stereocilia, and upregulated following the onset of MET and hearing. Loss of either protein results in elevated auditory brainstem response (ABR) thresholds, phosphatidylserine (PS) externalization, and rapid hair-cell degeneration, demonstrating that lipid homeostasis is crucial for OHC survival. Together, these findings establish ATP8B1 and TMEM30B as key regulators of membrane lipid asymmetry in sensory hair cells and establish TMEM30B as a novel deafness gene.

cell biology↗

bioRxiv2025

Modeling Alzheimer's Disease with APOE4 Neuron-Glial Brain Assembloids Reveals IGFBPs as Therapeutic Targets

Alzheimers disease (AD) research has been hindered by the lack of models that faithfully recapitulate the full profile of disease progression in a human genetic background. We developed a 3D assembloid model ("Masteroid") using iPSC-derived neurons, astrocytes, and microglia from APOE4/4 and isogenic control lines. Neurons were seeded with tau oligomers, then combined with astrocytes and microglia to form mature 3D Masteroids, followed by amyloid-{beta} oligomer exposure. After four weeks, AD-Masteroids exhibited hallmark pathologies, including extracellular amyloid-{beta} deposits, intracellular tau aggregation, neurodegeneration, astrogliosis, and microglial activation, with APOE4 exacerbating all phenotypes. Single-cell RNA sequencing further identified novel roles of IGFBP pathways in amyloid-{beta} and tau-mediated pathology. This innovative platform provides a robust system to dissect cellular and molecular mechanisms of AD progression and offers a powerful tool for therapeutic discovery. HighlightsO_LIThe 3D human neuron-glia assembloid ("Masteroid"), composed of neurons, astrocytes, microglia, and oligodendrocytes, faithfully recapitulates human brain ultrastructure and intercellular interactions. C_LIO_LIExposure to oligomeric tau and A{beta} induced hallmark Alzheimers pathologies, including amyloid deposition, tau aggregation, neurodegeneration, and gliosis. C_LIO_LIThe APOE4 genotype exacerbated all pathological features, highlighting its role in driving multicellular interactions that accelerate disease progression. C_LIO_LIThe IGF signaling axis was identified as a key mediator of A{beta}- and tau-induced pathology and a potential therapeutic target. C_LI Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=183 SRC="FIGDIR/small/683162v1_ufig1.gif" ALT="Figure 1"> View larger version (51K): org.highwire.dtl.DTLVardef@f91740org.highwire.dtl.DTLVardef@165726eorg.highwire.dtl.DTLVardef@13b957forg.highwire.dtl.DTLVardef@d40307_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

bioRxiv2025

PIP2-Tmie Interactions Drive Mammalian Hair Cell Slow Adaptation Independently of Myosin Motors

Sensory hair cells detect sound and balance through their apically located stereocilia bundles, converting mechanical stimuli into electrical signals via mechano-electrical transduction (MET) channels. These channels at the lower end of extracellular tip links connecting adjacent stereocilia are gated by tension. A key regulatory process of MET is slow adaptation, thought to enhance the auditory systems dynamic range. Traditionally, this process has been attributed to myosin motor activity. Here, we challenge this prevailing model and provide evidence for an alternative mechanism in which phosphatidylinositol 4,5-bisphosphate (PIP2) modulates slow adaptation via interactions with the MET complex protein TMIE. Remarkably, adaptation was rescued by exogenous PIP2 even when myosin motors were inhibited, highlighting PIP2s central role. Disruption of TMIE, a PIP2-binding protein, also impaired adaptation, and we implicate a PIP2 binding site between the channel candidate TMC1 and TMIE to mediate slow adaptation. These findings support a revised model in which PIP2-TMIE/TMC1 interactions mediate slow adaptation in hair cells.

biophysics↗

bioRxiv2025

A Tonotopic Regulatory Axis Governing Isoform-Specific MYO7A Expression in Cochlear Hair Cells

Myo7a, a gene mutated in Usher syndrome and non-syndromic deafness, encodes an unconventional myosin essential for hair cell function. Our previous work revealed that cochlear hair cells express distinct Myo7a isoforms with unique spatial and cell type-specific patterns. The canonical isoform (Myo7a-C) and a novel isoform (Myo7a-N) are co-expressed in outer hair cells (OHCs) but exhibit opposing tonotopic gradients, while inner hair cells (IHCs) primarily express Myo7a-C. These isoforms arise from distinct transcriptional start sites, indicating separate regulatory inputs. Here, we identify an intronic cis-regulatory element, EnhancerA, essential for tonotopically graded Myo7a expression. EnhancerA deletion reduces MYO7A protein levels in a tonotopically varied manner, disrupts hair bundle morphogenesis, alters OHC mechanotransduction, and leads to hair cell degeneration and hearing loss. We further identify SIX2, a tonotopically expressed transcription factor that may interact with EnhancerA to regulate Myo7a-N in OHCs. These findings define a cis-trans regulatory axis critical for isoform-specific Myo7a expression and cochlear function. SignificanceCochlear hair cells rely on the molecular motor MYO7A for mechanosensory function. Our previous study revealed that Myo7a isoforms are differentially expressed in auditory hair cells, however, the mechanisms regulating this isoform-specific expression remain unclear. In this study, we identify a cis-regulatory element, EnhancerA, that governs MYO7A expression in a tonotopically graded manner. Furthermore, we demonstrate that the transcription factor SIX2 plays a role in regulation of MYO7A, and is essential for hair cell maintenance. These findings establish a mechanistic link between cochlear position and protein isoform diversity, highlighting how hair cells adapt to frequency-specific mechanical demands. Importantly, the tonotopic regulatory function of EnhancerA also offers new avenues for targeted gene therapy in auditory disorders.

neuroscience↗

bioRxiv2025

Tonotopic Specialization of MYO7A Isoforms in Auditory Hair Cells

1.Mutations in Myo7a cause Usher syndrome type 1B and non-syndromic deafness, but the precise function of MYO7A in sensory hair cells remains unclear. We identify and characterize a novel isoform, MYO7A-N, expressed in auditory hair cells alongside the canonical MYO7A-C. Isoform-specific knock-in mice reveal that inner hair cells primarily express MYO7A-C, while outer hair cells express both isoforms in opposing tonotopic gradients. Both localize to the upper tip-link insertion site, consistent with a role in the tip link for mechanotransduction. Loss of MYO7A-N leads to outer hair cell degeneration and progressive hearing loss. Cryo-EM structures reveal isoform-specific differences at actomyosin interfaces, correlating with distinct ATPase activities. These findings reveal an unexpected layer of molecular diversity within the mechanotransduction machinery. We propose that MYO7A isoform specialization enables fine-tuning of tip-link tension, thus hearing sensitivity, and contributes to the frequency-resolving power of the cochlea.

neuroscience↗

bioRxiv2024

Spontaneous calcium transients in hair cell stereocilia

The hair bundle of auditory and vestibular hair cells converts mechanical stimuli into electrical signals through mechanoelectrical transduction (MET). The MET apparatus is built around a tip link that connects neighboring stereocilia that are aligned in the direction of mechanosensitivity of the hair bundle. Upon stimulation, the MET channel complex responds to changes in tip-link tension and allows a cation influx into the cell. Ca2+ influx in stereocilia has been used as a signature of MET activity. Using genetically encoded Ca2+ sensors (GCaMP3, GCaMP6s) and high-performance fluorescence confocal microscopy, we detect spontaneous Ca2+ transients in individual stereocilia in developing and fully formed hair bundles. We demonstrate that this activity is abolished by MET channel blockers and thus likely originates from putative MET channels. We observe Ca2+ transients in the stereocilia of mice in tissue explants as well as in vivo in zebrafish hair cells, indicating this activity is functionally conserved. Within stereocilia, the origin of Ca2+ transients is not limited to the canonical MET site at the stereocilia tip but is also present along the stereocilia length. Remarkably, we also observe these Ca2+ transients in the microvilli-like structures on the hair cell surface in the early stages of bundle development, prior to the onset of MET. Ca2+ transients are also present in the tallest rows of stereocilia in auditory hair cells, structures not traditionally thought to contain MET channels. We hypothesize that this newly described activity may reflect stochastic and spontaneous MET channel opening. Localization of these transients to other regions of the stereocilia indicates the presence of a pool of channels or channel precursors. Our work provides insights into MET channel assembly, maturation, function, and turnover.

cell biology↗

bioRxiv2024

Assessing Spns2-dependent S1P Transport as a Prospective Therapeutic Target using a New Chemical Probe

S1P (sphingosine 1-phosphate) receptor modulator (SRM) drugs interfere with lymphocyte trafficking by downregulating lymphocyte S1P receptors. While the immunosuppressive activity of SRM drugs has proved useful in treating autoimmune diseases such as multiple sclerosis, that drug class is beset by on-target liabilities such as initial dose bradycardia. The S1P that binds to cell surface lymphocyte S1P receptors is provided by S1P transporters. Mice born deficient in one of these, spinster homolog 2 (Spns2), are lymphocytopenic and have low lymph S1P concentrations. Such observations suggest that inhibition of Spns2-mediated S1P transport might provide another therapeutically beneficial method to modulate immune cell positioning. We report here results using a novel S1P transport blocker (STB), SLF80821178, to investigate the consequences of S1P transport inhibition in rodents. We found that SLF80821178 is efficacious in a multiple sclerosis model but - unlike the SRM fingolimod - neither decreases heart rate nor compromises lung endothelial barrier function. Notably, although Spns2 null mice have a sensorineural hearing defect, mice treated chronically with SLF80821178 have normal hearing acuity. STBs such as SLF80821178 evoke a dose-dependent decrease in peripheral blood lymphocyte counts, which affords a reliable pharmacodynamic marker of target engagement. However, the maximal reduction in circulating lymphocyte counts in response to SLF80821178 is substantially less than the response to SRMs such as fingolimod (50% vs. 90%) due to a lesser effect on T lymphocyte sub-populations by SLF80821178. Finally, in contrast to results obtained with Spns2 deficient mice, lymph S1P concentrations were not significantly changed in response to administration of STBs at doses that evoke maximal lymphopenia, which indicates that current understanding of the mechanism of action of S1P transport inhibitors is incomplete.

pharmacology and toxicology↗

bioRxiv2023

Differential regulation of hair cell actin cytoskeleton mediated by SRF and MRTFB

The MRTF-SRF pathway has been extensively studied for its crucial role in driving the expression of a large number of genes involved in actin cytoskeleton of various cell types. However, the specific contribution of MRTF-SRF in hair cells remains unknown. In this study, we showed that hair cell-specific deletion of Srf or Mrtfb, but not Mrtfa, leads to similar defects in the development of stereocilia dimensions and the maintenance of cuticular plate integrity. We used FACS-based hair cell RNA-seq analysis to investigate the mechanistic underpinnings of the changes observed in Srf and Mrtfb mutants, respectively. Interestingly, the transcriptome analysis revealed distinct profiles of genes regulated by Srf and Mrtfb, suggesting different transcriptional regulation mechanisms of actin cytoskeleton activities mediated by Srf and Mrtfb. Exogenous delivery of calponin 2 using Adeno-associated virus transduction in Srf mutants partially rescued the impairments of stereocilia dimensions and the F-actin intensity of cuticular plate, suggesting the involvement of Cnn2, as an Srf downstream target, in regulating the hair bundle morphology and cuticular plate actin cytoskeleton organization. Our study uncovers, for the first time, the unexpected differential transcriptional regulation of actin cytoskeleton mediated by Srf and Mrtfb in hair cells, and also demonstrates the critical role of SRF-CNN2 in modulating actin dynamics of the stereocilia and cuticular plate, providing new insights into the molecular mechanism underlying hair cell development and maintenance.

cell biology↗

bioRxiv2022

Stress-Induced Mucosal Layer Disruption Drives Gut Dysbiosis and Depressive-like Behaviors

Depression is a prevalent psychological condition with limited treatment options. While its etiology is multifactorial, both chronic stress and changes in the microbiome are associated with disease pathology. In depression, stress is known to induce microbiome dysbiosis, defined here as a change in microbial composition associated with a pathological condition. This state of dysbiosis is then known to feedback on depressive symptoms. While studies have demonstrated that targeted restoration of the microbiome can alleviate depressive-like symptoms in mice, translating these findings to human patients has proven challenging due to the complexity of the human microbiome. As such, there is an urgent need to identify factors upstream of microbial dysbiosis. Here we investigate the role of mucin 13 as an upstream mediator of microbiome composition changes. Using a model of chronic stress, we show that the mucosal protein, mucin 13, is selectively reduced after psychological stress exposure. We further demonstrate that the reduction of Muc13 is mediated by the Hnf4 transcription factor family. Finally, we determine that deleting Muc13 is sufficient to drive microbiome shifts and despair behaviors. These findings shed light on the mechanisms behind stress-induced microbial changes and reveal a regulator of mucin 13 expression. SummaryIn this paper, authors identified a pathway by which stress induces microbiome shifts. They found that psychological stress selectively alters a key mucosal protein, mucin 13, which in turn modifies the microbial niche to induce changes in bacterial composition.

microbiology↗

bioRxiv2021

Repair of Noise-Induced Damage to Stereocilia F-actin Cores is Facilitated by XIRP2

Prolonged exposure to loud noise has been shown to affect inner ear sensory hair cells in a variety of deleterious manners, including damaging the stereocilia core. The damaged sites can be visualized as "gaps" in phalloidin staining of F-actin, and the enrichment of monomeric actin at these sites, along with an actin nucleator and crosslinker, suggests that localized remodeling occurs to repair the broken filaments. Herein we show that gaps in mouse auditory hair cells are largely repaired within one week of traumatic noise exposure through the incorporation of newly synthesized actin. Additionally, we report that XIRP2 is required for the repair process and facilitates the enrichment of monomeric{gamma} -actin at gaps through its LIM domain-containing C-terminus. Our study describes a novel process by which hair cells can recover from sub-lethal hair bundle damage and which may contribute to recovery from temporary hearing threshold shifts and the prevention of age-related hearing loss.

neuroscience↗

bioRxiv2018

LMO7 deficiency reveals the significance of the cuticular plate for hearing function

Sensory hair cells, the mechanoreceptors of the auditory and vestibular system, harbor two specialized organelles, the hair bundle and the cuticular plate. Both subcellular structures have adapted to facilitate the remarkable sensitivity and speed of hair cell mechanotransduction. While the mechanosensory hair bundle is extensively studied, the molecules and mechanisms mediating the development and function of the cuticular plate are poorly understood. The cuticular plate is believed to provide a rigid foundation for stereociliar pivot movements, but specifics about its function, especially the significance of its integrity for long-term maintenance of hair cell mechanotransduction, are not known. In this study, we describe the discovery of a hair cell protein called LIM only protein 7 (LMO7). In the hair cell, LMO7 is specifically localized in the cuticular plate. Lmo7 KO mice suffer multiple deficiencies in the cuticular plate, including reduced filamentous actin density and abnormal length and distribution of stereociliar rootlets. In addition to the cuticular plate defects, older Lmo7 KO mice develop abnormalities in inner hair cell stereocilia. Together, these defects affect cochlear tuning and sensitivity and give rise to late-onset progressive hearing loss.

neuroscience↗

bioRxiv2018

Necroptosis and apoptosis contribute to cisplatin and aminoglycoside ototoxicity

Ototoxic side effects of cisplatin and aminoglycosides have been extensively studied, but no therapy is available to date. Sensory hair cells, upon exposure to cisplatin or aminoglycosides, undergo apoptotic and necrotic cell death. Blocking these cell death pathways has therapeutic potential in theory, but incomplete protection and lack of therapeutic targets in the case of necrosis, has hampered the development of clinically applicable drugs. Over the past decade, a novel form of necrosis, termed necroptosis, was established as an alternative cell death pathway. Necroptosis is distinguished from passive necrotic cell death, in that it follows a cellular program, involving the receptor-interacting protein kinases 1 and 3 (RIPK1 and 3). In this study, we used pharmacological and genetic intervention to test the relative contributions of necroptosis and caspase-8-mediated apoptosis towards cisplatin and aminoglycoside ototoxicity. We find that ex vivo, only apoptosis contributes to cisplatin and aminoglycoside ototoxicity, while in vivo, both necroptosis and apoptosis are involved. Inhibition of necroptosis and apoptosis using pharmacological compounds is thus a viable strategy to ameliorate aminoglycoside and cisplatin ototoxicity.\n\nSignificance statementThe clinical application of cisplatin and aminoglycosides is limited due to ototoxic side effects. Here, using pharmaceutical and genetic intervention, we present evidence that two types of programmed cell death, apoptosis and necroptosis, contribute to aminoglycoside and cisplatin ototoxicity. Key molecular factors mediating necroptosis are well characterized and druggable, presenting new avenues for pharmaceutical intervention.

neuroscience↗