Biology subjects

Chin, M.

Publications and source records attributed to Chin, M..

8 recordsLinked to original sources

bioRxiv2026

Engineered proteins to restore and enhance neurotransmitter release

Synapse dysfunction is a hallmark feature of many neurological diseases. Synaptic transmission is initiated in nerve terminals, where active zone protein complexes control vesicle fusion for neurotransmitter release. Here, we engineer proteins that mediate active zone functions and demonstrate their use for reconstituting and strengthening neurotransmission. A protein composed of CaV{beta}4 and the RIM1 zinc finger, {beta}4-Zn, restored neurotransmitter release after active zone disruption through recruitment of Munc13. We develop {beta}4-MC, derived from the Munc13-1 MUN and C2C domains, which bypasses Munc13 recruitment and directly mediates vesicle docking, priming and fusion after active zone disruption. In {beta}4-MC, MUN domain functions are dispensable for docking, but active MUN and C2C domains are both necessary for neurotransmitter release. In wild-type mouse and human neurons, {beta}4-MC but not {beta}4-Zn strengthens neurotransmitter release. Furthermore, {beta}4-Zn and {beta}4-MC restore and enhance dopamine release in the mouse striatum, respectively. Hence, {beta}4 proteins are engineered secretory proteins with therapeutic potential as enhancers of synaptic function.

neuroscience↗

bioRxiv2026

Ancestral gene flow shaped the singular origin of the Amazon molly

The evolutionary origins of asexuality remain poorly understood, despite extensive research on its ecological and evolutionary consequences. Asexuality often arises through hybridization between species with intermediate genomic divergence, implying that hybrid-induced asexuality may be partly repeatable. The Amazon molly (Poecilia formosa), the first asexual vertebrate known to science, challenges this view: repeated experimental crosses between its extant parental species have failed to recreate a stable Amazon molly-like lineage. This apparent paradox gave rise to the Rare Formation Hypothesis, which proposes that stable asexuality requires an exceptionally specific genomic combination. Here, we combine experimental crosses, molecular cytogenetics, and population genomics to test whether ancestral introgression before the hybrid speciation event set the stage for the singular origin of the Amazon molly. We show that most experimental hybrids are viable but sexual, but that a subset of F1 hybrids produce unreduced eggs through a mechanism distinct from that of the Amazon molly. Population genomic analyses reveal that introgression between parental species likely predated the formation of the Amazon molly, and shared homozygous tracts across Amazon molly genomes support inheritance from admixed progenitors. Together, our findings reconcile the repeatable and contingent views of the origin of asexuality, suggesting that ancestral introgression may be the missing mechanism assembling the rare genomic combinations required for seemingly unrepeatable evolutionary innovations, including the emergence of asexual species.

evolutionary biology↗

bioRxiv2024

Novel high-content and open-source image analysis tools for profiling mitochondrial morphology in neurological cell models

Mitochondria undergo dynamic morphological changes depending on cellular cues, stress, genetic factors, or disease. The structural complexity and disease-relevance of mitochondria have stimulated efforts to generate image analysis tools for describing mitochondrial morphology for therapeutic development. Using high-content analysis, we measured multiple morphological parameters and employed unbiased feature clustering to identify the most robust pair of texture metrics that described mitochondrial state. Here, we introduce a novel image analysis pipeline to enable rapid and accurate profiling of mitochondrial morphology in various cell types and pharmacological perturbations. We applied a high-content adapted implementation of our tool, MitoProfilerHC, to quantify mitochondrial morphology changes in i) a mammalian cell dose response study and ii) compartment-specific drug effects in primary neurons. Next, we expanded the usability of our pipeline by using napari, a Python-powered image analysis tool, to build an open-source version of MitoProfiler and validated its performance and applicability. In conclusion, we introduce MitoProfiler as both a high-content-based and an open-source method to accurately quantify mitochondrial morphology in cells, which we anticipate to greatly facilitate mechanistic discoveries in mitochondrial biology and disease.

cell biology↗

bioRxiv2023

The intracellular C-terminus confers compartment-specific targeting of voltage-gated Ca2+ channels

To achieve the functional polarization that underlies brain computation, neurons sort protein material into distinct compartments. Ion channel composition, for example, differs between axons and dendrites, but the molecular determinants for their polarized trafficking remain obscure. Here, we identify the mechanisms that target voltage-gated Ca2+ channels (CaVs) to distinct subcellular compartments. In hippocampal neurons, CaV2s trigger neurotransmitter release at the presynaptic active zone, and CaV1s localize somatodendritically. After knockout of all three CaV2s, expression of CaV2.1, but not of CaV1.3, restores neurotransmitter release. Chimeric CaV1.3 channels with CaV2.1 intracellular C-termini localize to the active zone, mediate synaptic vesicle exocytosis, and render release fully sensitive to blockade of CaV1 channels. This dominant targeting function of the CaV2.1 C-terminus requires an EF hand in its proximal segment, and replacement of the CaV2.1 C-terminus with that of CaV1.3 abolishes CaV2.1 active zone localization. We conclude that the intracellular C-termini mediate compartment-specific CaV targeting.

neuroscience↗

bioRxiv2021

Humanization of antibodies using a machine learning approach on large-scale repertoire data

Monoclonal antibody therapeutics are often produced from non-human sources (typically murine), and can therefore generate immunogenic responses in humans. Humanization procedures aim to produce antibody therapeutics that do not elicit an immune response and are safe for human use, without impacting efficacy. Humanization is normally carried out in a largely trial-and-error experimental process. We have built machine learning classifiers that can discriminate between human and non-human antibody variable domain sequences using the large amount of repertoire data now available. Our classifiers consistently outperform existing best-in-class models, and our output scores exhibit a negative relationship with the experimental immunogenicity of existing antibody therapeutics. We used our classifiers to develop a novel, computational humanization tool, Hu-mAb, that suggests mutations to an input sequence to reduce its immunogenicity. For a set of existing therapeutics with known precursor sequences, the mutations suggested by Hu-mAb show significant overlap with those deduced experimentally. Hu-mAb is therefore an effective replacement for trial- and-error humanization experiments, producing similar results in a fraction of the time. Hu-mAb is freely available to use at opig.stats.ox.ac.uk/webapps/humab.

immunology↗

bioRxiv2020

The Potassium Channel Subunit Kvβ1 is Required for Synaptic Facilitation

Analysis of the presynaptic action potentials (APsyn) role in synaptic facilitation in hippocampal pyramidal neurons has been difficult due to size limitations of axons. We overcame these size barriers by combining high resolution optical recordings of membrane potential, exocytosis and Ca2+ in cultured hippocampal neurons. These recordings revealed a critical and selective role for Kv1 channel inactivation in synaptic facilitation of excitatory hippocampal neurons. Presynaptic Kv1 channel inactivation was mediated by the Kv{beta}1 subunit, and had a surprisingly rapid onset that was readily apparent even in brief physiological stimulation paradigms including paired-pulse stimulation. Genetic depletion of Kv{beta}1 blocked all broadening of the APsyn during high frequency stimulation and eliminated synaptic facilitation without altering the initial probability of vesicle release. Thus using all quantitative optical measurements of presynaptic physiology, we reveal a critical role for presynaptic Kv channels in synaptic facilitation at small presynaptic terminals of the hippocampal neurons upstream of exocytic machinery. SignificanceNerve terminals generally engage in two opposite and essential forms of synaptic plasticity (facilitation or depression) during high frequency stimulation that play critical roles in learning and memory. Measurements of the electrical impulses (action potentials) underlying these two forms of plasticity has been difficult in small nerve terminals due to their size. In this study we deployed a combination of optical measurements of vesicle fusion and membrane voltage to overcome this previous size barrier. Here, we found a unique molecular composition of Kv1 channel {beta}-subunits that causes broadening of the presynaptic action essential to synaptic facilitation. Disruption of the Kv{beta}1 inactivation mechanism switches excitatory nerve terminals into a depressive state, without any disruption to initial probability of vesicle fusion.

neuroscience↗

bioRxiv2018

Synaptic vesicles undock and then transiently dock after an action potential

Synaptic vesicles fuse with the plasma membrane to release neurotransmitter following an action potential, after which new vesicles must dock to refill vacated release sites. To capture synaptic vesicle exocytosis at cultured mouse hippocampal synapses, we induced single action potentials by electrical field stimulation then subjected neurons to high-pressure freezing to examine their morphology by electron microscopy. During synchronous release, multiple vesicles can fuse at a single active zone; this multivesicular release is augmented by increasing extracellular calcium. Fusions during synchronous release are distributed throughout the active zone, whereas fusions during asynchronous release are biased toward the center of the active zone. Immediately after stimulation, the total number of docked vesicles across all synapses decreases by [~]40%. Between 8 and 14 ms, new vesicles are recruited to the plasma membrane and fully replenish the docked pool in a calcium-dependent manner, but docking of these vesicles is transient and they either undock or fuse within 100 ms. These results demonstrate that recruitment of synaptic vesicles to release sites is rapid and reversible.

neuroscience↗

bioRxiv2018

Mechanical and Microstructural Properties of Pediatric Anterior Cruciate Ligaments and Autograft Tendons used for Reconstruction

BackgroundOver the last several decades there has been a steady increase in pediatric ACL tears, particularly in young female basketball and soccer players. Because allograft tissue for pediatric ACL reconstruction (ACLR) has shown high rates of failure, autograft tissue may be the best option for ACLR in this population. However, the differences in structure and mechanical behavior of these tissues are not clear.\n\nPurposeThis study sought to characterize mechanical and microstructural properties in pediatric ACLs and autograft tissues using a rare cadaveric cohort (mean age 9.2 years).\n\nStudy DesignDescriptive laboratory study.\n\nMethodsACLs, patellar tendons, quadriceps tendons, semitendinosus tendons, and iliotibial bands (ITBs) were harvested from five fresh-frozen pediatric knee specimens (3M, 2F) and subjected to a tensile loading protocol. A subset of contralateral tissues were analyzed using brightfield, polarized light, and transmission electron microscopy.\n\nResultsPatellar tendons exhibited values for ultimate stress (5.2{+/-}3.1 MPa), ultimate strain (35.3{+/-}12.5%), and Youngs Modulus (27.0{+/-}8.0 MPa) that were most similar to the ACL (5.2{+/-}2.2 MPa; 31.4{+/-}9.9%; 23.6{+/-}15.5 MPa). Semitendinosus tendons and ITBs were stronger but less compliant than the quadriceps or patellar tendons. ITBs exhibited crimp wavelengths (24.3{+/-}3.1 um) and collagen fibril diameters (67.5{+/-}19.5 nm) that were most similar to the ACL (24.4{+/-}3.2 um; 69.7{+/-}20.3 nm).\n\nConclusionThe mechanical properties of the patellar tendon were almost identical to that of the ACL. The ITB exhibited increased strength and similar microstructure to the native ACL. These findings are not entirely congruent to studies examining adult tissues.\n\nClinical RelevanceResults suggest that ITB tissue may be the preferable choice as an autograft tissue in pediatric ACL reconstructions.\n\nKey TermsPediatric, ACL reconstruction, mechanical properties, microstructural properties, patella tendon grafts, quadriceps tendon grafts, hamstring grafts\n\nWhat is Known about the SubjectDue to the extreme rarity of pediatric cadaveric specimens, very little is known about these tissues.\n\nWhat this Study Adds to Existing KnowledgeThis suite of data can be used to further optimize the design and selection of grafts for reconstruction and may provide insight into the development of constitutive musculoskeletal models.

bioengineering↗