Model System Research Articles

Reevaluating infrared spectroscopic signatures of polaron trapping in a chemically doped conducting polymer.

Charge conductivity in conducting polymers is typically improved by increasing carrier density via chemical oxidation. However, the resulting electrostatic stabilization of the carriers by the dopant ions, combined with their nanostructural environment, are both known to crucially affect charge trapping. Although the effects of charge-ion electrostatic interactions on carrier trapping have been well-characterized using conventional infrared (IR) spectroscopy, the impacts of the polymer chain ordering and energetic environment are difficult to disentangle. In this study, we examine the limitations of conventional IR absorption spectroscopy and introduce a complementary spectroscopic approach capable of discerning polaron trapping more generally. To do so, we investigated films of poly(3-hexylthiophene-2,5-diyl) (P3HT) chemically doped using four different oxidants, of which each preferentially dopes the amorphous and crystalline (lamellar) phases to varying extents. Using this model system, we observed counterintuitive shifts in the polaron IR absorption band, indicating that IR spectroscopy is a clear reporter of trapping only when the carriers exclusively reside in the lamellar phase and in the absence of bipolarons or coupled polarons. Alternatively, we found that polaron excited state dynamics, probed using ultrafast near-infrared transient absorption spectroscopy, more clearly report on charge trapping. This study demonstrates near-infrared transient absorption spectroscopy as a complementary tool for probing charge trapping in conducting polymers when doping induces carriers in different nanostructural environments.

The role of transcription bodies in gene expression: what embryos teach us.

Transcription does not occur diffusely throughout the nucleus but is concentrated in specific areas. Areas of accumulated transcriptional machinery have been called clusters, hubs, or condensates, while transcriptionally active areas have been referred to as transcription factories or transcription bodies. Despite the widespread occurrence of transcription bodies, it has been difficult to study their assembly, function, and effect on gene expression. This review highlights the advantages of developmental model systems such as zebrafish and fruit fly embryos, in addressing these questions. We focus on three important discoveries that were made in embryos. (i) It had previously been suggested that, in transcription bodies, the different steps of the transcription process are organized in space. We explore how work in embryos has revealed that they can also be organized in time. In this case, transcription bodies mature from transcription factor clusters to elongating transcription bodies. This type of organization has important implications for transcription body function. (ii) The relevance of clustering for in vivo gene regulation has benefited greatly from studies in embryos. We discuss examples in which transcription bodies regulate developmental gene expression by compensating for low transcription factor concentrations and low-affinity enhancers. Finally, (iii) while accumulations of transcriptional machinery can facilitate transcription locally, work in embryos showed that transcription bodies can also sequester the transcriptional machinery, modulating the availability for activity at other sites. In brief, the reviewed literature highlights the properties of developmental model organisms that make them powerful systems for uncovering the form and function of transcription bodies.

The need for robust model systems in the study of hybrid interfaces for photocatalysis and photoelectrocatalysis.

Small molecule conversion to value-added products using renewable energy sources has emerged as a promising strategy to mitigate our reliance on fossil fuels. Hybrid materials that integrate the strengths of photoabsorbers and co-catalysts (electrocatalysts) are essential for maximizing the efficiency of photochemical (PC) and photoelectrochemical (PEC) systems. In this perspective, we will focus on the need for fundamental studies with a strong emphasis on the importance of beginning with well-defined hybrid interfaces. A particular focus is given to small molecule adsorption studies that correlate surface structure and chemistry to reactivity, highlighting its potential in characterizing complex interfaces. We also make the case for understanding how light and electrochemical environments influence surface structure, adsorption, and reactivity and should be considered in model hybrid system design. Finally, we provide a framework to connect the theory and experiment of model hybrid surfaces to provide a molecular understanding of PC and PEC at these interfaces and accelerate our integration of these materials into real systems capable of meeting our renewable energy needs.

Lyotropic Liquid Crystal Mediated Assembly of Donor Polymers Enhances Efficiency and Stability of Blade-Coated Organic Solar Cells.

Conjugated polymers can undergo complex, concentration-dependent self-assembly during solution processing, yet little is known about its impact on film morphology and device performance of organic solar cells. Herein, lyotropic liquid crystal (LLC) mediated assembly across multiple conjugated polymers is reported, which generally gives rise to improved device performance of blade-coated non-fullerene bulk heterojunction solar cells. Using D18 as a model system, the formation mechanism of LLC is unveiled employing solution X-ray scattering and microscopic imaging tools: D18 first aggregates into semicrystalline nanofibers, then assemble into achiral nematic LLC which goes through symmetry breaking to yield a chiral twist-bent LLC. The assembly pathway is driven by increasing solution concentration - a common driving force during evaporative assembly relevant to scalable manufacturing. This assembly pathway can be largely modulated by coating regimes to give 1) lyotropic liquid crystalline assembly in the evaporation regime and 2) random fiber aggregation pathway in the Landau-Levich regime. The chiral liquid crystalline assembly pathway resulted in films with crystallinity 2.63 times that of films from the random fiber aggregation pathway, significantly enhancing the T80 lifetime by 50-fold. The generality of LLC-mediated assembly and enhanced device performance is further validated using polythiophene and quinoxaline-based donor polymers.

Identifying Endogenous Proteins of Perennial Ryegrass (Lolium perenne) with Ex Vivo Antioxidant Activity

Background: During the initial steps of green biorefining aimed at protein recovery, endogenous proteins and enzymes, along with, e.g., phytochemical constituents, are decompartmentalized into a green juice. This creates a highly dynamic environment prone to a plethora of reactions including oxidative protein modification and deterioration. Obtaining a fundamental understanding of the enzymes capable of exerting antioxidant activity ex vivo could help mitigate these reactions for improved product quality. Methods: In this study, we investigated perennial ryegrass (Lolium perenne var. Abosan 1), one of the most widely used turf and forage grasses, as a model system. Using size exclusion chromatography, we fractionated the green juice to investigate in vitro antioxidant properties and coupled this with quantitative bottom-up proteomics, GO-term analysis, and fraction-based enrichment. Results: Our findings revealed that several enzymes, such as superoxide dismutase and peroxiredoxin proteoforms, already known for their involvement in in vivo oxidative protection, are enriched in fractions displaying increased in vitro antioxidant activity, indicating retained activity ex vivo. Moreover, this study provides the most detailed characterization of the L. perenne proteome today and delivers new insights into protein-level partitioning during wet fractionation. Conclusions: Ultimately, this work contributes to a better understanding of the first steps of green biorefining and provides the basis for process optimization.

Efficient Confinement of Solid Capacity Booster Powder as Monolithic Structures for High Performance Redox Mediated Flow Batteries

AbstractConfinement of solid electroactive materials in the external reservoirs of Redox‐Mediated Flow Batteries (RMFB) is of critical importance for the development of this family of battery technologies. Herein, an efficient strategy that is based on a flow‐through configuration is proposed. Confinement of all solid particles in a single porous block (so‐called monolith) that occupies the entire reservoir brings practical and fundamental advantages. The improved flow distribution across the reservoir for the flow‐through configuration enables enhanced kinetics and utilization rates (twice the utilization rate in 20% shorter time). Pressure drop induced by the flow‐through configuration is easily reduced by changing the reservoir geometry becoming negligible in comparison to the drop induced by the cell (value for the monolith can be as low as 0.2% of the cell value). Additionally, determination of intrinsic properties of the steady monolith prior to its encapsulation enables knowing textural properties of the reservoir which are required for fundamental aspects. While ferrocyanide – Prussian Blue (redox mediator – solid booster) is used as model system here, the versatility of this strategy enables its implementation in other systems including future chemistries.

A novel scoring system for better management of small bowel obstruction.

Due to the lack of a comprehensive evaluation of the prognosis of small bowel obstruction (SBO), recent clinical strategies have remained subjective and controversial. The recognition of pretreatment risk factors and tailored treatment could improve SBO outcomes. A series of posttreatment laboratory tests were integrated into a two-step clustering (TSC) analysis. The TSC outcome was determined according to different predictor importance (PI). A risk score (RS) system for the TSC outcome model was constructed by multivariable analysis. Receiver operating characteristic (ROC) curves and the area under the curve (AUC) were calculated to assess prediction accuracy. Of the 355 patients, 66 (18.6%) were sorted into the better prognosis group (BPG), 149 (42.0%) were sorted into the poor prognosis group (PPG), and 140 (39.4%) were sorted into the severe prognosis group (SPG) by TSC analysis. For the TSC outcome, four variables with higher PI were identified, namely, Ca (PI = 1), albumin (PI = 0.62), WBC count (PI = 0.5) and NE% (PI = 0.45). Compared with the SPG, the BPG presented better outcomes after surgery events. The TSC outcome model was efficient in distinguishing the duration of bowel function recovery and hospital stay by Kaplan‒Meier curves. Via multivariate analysis, a RS consisting of four risk factors, namely, constipation duration (OR = 1.002), APTT (OR = 0.923), PT (OR = 1.449) and PCT (OR = 1.540), was identified. The AUC of the RS on the TSC outcome model was 0.719 (95% CI, 0.635-0.804). A novel TSC outcome model and RS system was constructed to comprehensively reflect the tailored treatment, surgical events and posttreatment recovery for SBO patients.

Enhanced image processing and storage for defect evaluation in BIM of inspected steel bridges

Every structure undergoes a maintenance lifecycle, with increasing emphasis on structural health monitoring, defect diagnosis, and repair. As the demand for timely, effective, practical, and cost-efficient solutions grows, new techniques and processes are continually being developed. The traditionally paper-based methods of bridge inspection, defect diagnosis, and repair are evolving into digital processes. The overall efficiency targeted by this digital transformation process can be increased by 35–50 percent when criteria such as time, cost, accuracy and applicability are evaluated. This paper presents an automated data collection and analysis procedure related to structural integrity evaluation. The study focuses on optimizing human-operated inspection procedures by incorporating advanced technologies, such as image processing techniques for defect identification in a digital environment, and integrating defect information into Building Information Modeling (BIM) systems. These focal points and processes, aiming to identify defect identification, and defect information management in BIM environment, are further explored and demonstrated through a case study involving a steel bridge. At the beginning of the study, approximately 160 defect images were collected, examined and some of them were selected for visualization purposes. The authors table a procedure that can be followed, starting with storing defect images and ending with defect visualization in the BIM environment, and present a discussion on the advantages and limits of the process by examining concepts such as automated data collection by drones, machine vision-based damage identification by color detection technique, BIM and Industry Foundation Classes standardisation applied to inspection data.

A cost-effective, high-throughput, highly accurate genotyping method for outbred populations.

Affordable sequencing and genotyping methods are essential for large-scale genome-wide association studies. While genotyping microarrays and reference panels for imputation are available for human subjects, nonhuman model systems often lack such options. Our lab previously demonstrated an efficient and cost-effective method to genotype heterogeneous stock rats using double-digest genotyping by sequencing. However, low-coverage whole-genome sequencing offers an alternative method that has several advantages. Here, we describe a cost-effective, high-throughput, high-accuracy genotyping method for N/NIH heterogeneous stock rats that can use a combination of sequencing data previously generated by double-digest genotyping by sequencing and more recently generated by low-coverage whole-genome sequencing data. Using double-digest genotyping-by-sequencing data from 5,745 heterogeneous stock rats (mean 0.21× coverage) and low-coverage whole-genome sequencing data from 8,760 heterogeneous stock rats (mean 0.27× coverage), we can impute 7.32 million biallelic single-nucleotide polymorphisms with a concordance rate > 99.76% compared to high-coverage (mean 33.26× coverage) whole-genome sequencing data for a subset of the same individuals. Our results demonstrate the feasibility of using sequencing data from double-digest genotyping by sequencing or low-coverage whole-genome sequencing for accurate genotyping and demonstrate techniques that may also be useful for other genetic studies in nonhuman subjects.

Deep Learning and Single-Molecule Localization Microscopy Reveal Nanoscopic Dynamics of DNA Entanglement Loci.

Understanding molecular dynamics at the nanoscale remains challenging due to limitations in the temporal resolution of current imaging techniques. Deep learning integrated with Single-Molecule Localization Microscopy (SMLM) offers opportunities to probe these dynamics. Here, we leverage this integration to reveal entangled polymer dynamics at a fast time scale, which is relatively poorly understood at the single-molecule level. We used Lambda DNA as a model system and modeled their entanglement using the self-avoiding wormlike chain model, generated simulated localizations along the contours, and trained the deep learning algorithm on these simulated images to predict chain contours from sparse localization data. We found that the localizations are heterogeneously distributed along the contours. Our assessments indicated that chain entanglement creates local diffusion barriers for switching buffer molecules, affecting the photoswitching kinetics of fluorescent dyes conjugated to the DNA molecules at discrete DNA segments. Tracking these segments demonstrated stochastic and subdiffusive migration of the entanglement loci. Our approach provides direct visualization of nanoscale polymer dynamics and local molecular environments previously inaccessible to conventional imaging techniques. In addition, our results suggest that the switching kinetics of the fluorophores in SMLM can be used to characterize nanoscopic local environments.

ACTIVE TRANSFORMATION OF PLANES DURING FORMATION OF DISCRETE FRAMES WHITH A STATIC-GEOMETRIC METHOD

Various transformations have found widespread use in applied geometry problems in simulating discrete frameworks of different surfaces with given properties. The paper presents a mathematical apparatus of active coordinate transformation, designed to solve problems of discrete geometric modeling. Under the active transformation of coordinates, the authors propose to consider a clear match between the points of the original and new coordinate systems, while maintaining their numerical correspondence, when the numerical values of the parameters of the original coordinate system will transition to the numerical values of the parameters of the new coordinate system. The paper describes the peculiarities of using active coordinate transformation. In the study is proposes to use the properties of the active plane transformation when switching from The work a rectangular Cartesian coordinate system to a rectangular cylindrical coordinate system for further modeling of discrete frameworks of curved surfaces. The authors of the article focus on that there are many discrete modeling methods among which the generalized static-geometric method of Professor Kovalev S.M. The work demonstrates the possibilities of this method by additional use of active coordinate transformation. It has been proved that the advantages and features of active transformation of coordinates can be used in providing the modeled surface with certain properties necessary for the designer or architect in the process of creating a particular modeled image. Using an active coordinate transformation will simplify the process of forming new geometric shapes of curved surfaces, which are quite difficult to describe analytically. The information presented in the work will be useful for architects and designers in the formation of discrete frames of various surfaces

The genomic landscape, causes, and consequences of extensive phylogenomic discordance in murine rodents.

A species tree is a central concept in evolutionary biology whereby a single branching phylogeny reflects relationships among species. However, the phylogenies of different genomic regions often differ from the species tree. Although tree discordance is widespread in phylogenomic studies, we still lack a clear understanding of how variation in phylogenetic patterns is shaped by genome biology or the extent to which discordance may compromise comparative studies. We characterized patterns of phylogenomic discordance across the murine rodents - a large and ecologically diverse group that gave rise to the laboratory mouse and rat model systems. Combining recently published linked-read genome assemblies for seven murine species with other available rodent genomes, we first used ultra-conserved elements (UCEs) to infer a robust time-calibrated species tree. We then used whole genomes to examine finer-scale patterns of discordance across ∼12 million years of divergence. We found that proximate chromosomal regions tended to have more similar phylogenetic histories. There was no clear relationship between local tree similarity and recombination rates in house mice, but we did observe a correlation between recombination rates and average similarity to the species tree. We also detected a strong influence of linked selection whereby purifying selection at UCEs led to appreciably less discordance. Finally, we show that assuming a single species tree can result in substantial deviation from the results with gene trees when testing for positive selection under different models. Collectively, our results highlight the complex relationship between phylogenetic inference and genome biology and underscore how failure to account for this complexity can mislead comparative genomic studies.

An orphan gene is essential for efficient sperm entry into eggs in Drosophila melanogaster.

While spermatogenesis has been extensively characterized in the Drosophila melanogaster model system, very little is known about the genes required for fly sperm entry into eggs. We identified a lineage-specific gene, which we named katherine johnson (kj), that is required for efficient fertilization. Males that do not express kj produce and transfer sperm that are stored normally in females, but sperm from these males enter eggs with severely reduced efficiency. Using a tagged transgenic rescue construct, we observed that the KJ protein localizes around the edge of the nucleus at various stages of spermatogenesis but is undetectable in mature sperm. These data suggest that kj exerts an effect on sperm development, the loss of which results in reduced fertilization ability. Interestingly, KJ protein lacks detectable sequence similarity to any other known protein, suggesting that kj could be a lineage-specific orphan gene. While previous bioinformatic analyses indicated that kj was restricted to the melanogaster group of Drosophila, we identified putative orthologs with conserved synteny, male-biased expression, and predicted protein features across the genus, as well as likely instances of gene loss in some lineages. Thus, kj was likely present in the Drosophila common ancestor. It is unclear whether its role in fertility had already evolved at that time or developed later in the lineage leading to D. melanogaster. Our results demonstrate a new aspect of male reproduction that has been shaped by a lineage-specific gene and provide a molecular foothold for further investigating the mechanism of sperm entry into eggs in Drosophila.

Bacterial proliferation pattern formation

Bacteria can form a great variety of spatially heterogeneous cell density patterns, ranging from simple concentric rings to dynamical spiral waves appearing in growing colonies. These pattern formation phenomena are important as they reflect how cellular processes such as metabolism operate in heterogeneous chemical environments. In the laboratory, they can be studied in simplified setups, where spatial gradients of oxygen and nutrients are externally imposed, and cells are immobilized in a gel matrix. An intriguing example, observed in such setups over 80 years ago, is the sequential formation of narrow bands of high cell density, taking place even for a clonal population. However, key aspects of the dynamics of band formation remained obscure. Using time-lapse imaging of replicate transparent columns in simplified growth media, we first quantify the precision of the positioning and timing of band formation. We also show that the appearance and position of different bands can be modulated independently. This “modularity” is suggested by the observation that different bands differ in their gene expression, and it is reproduced by a theoretical model based on the existence of internal metabolic states and the induction of a pH gradient. Finally, we can also modify the observed pattern formation by introducing genetic modifications that impair selected metabolic pathways. In our opinion, the possibility of precise measurements and controls, together with the simplicity and richness of the “proliferation pattern formation” phenomenon, can make it a model system to study the response of cellular processes to heterogeneous environments. Published by the American Physical Society 2025

Repartitioning the Hamiltonian in many-body second-order Brillouin-Wigner perturbation theory: Uncovering new size-consistent models.

Second-order Møller-Plesset perturbation theory is well-known as a computationally inexpensive approach to the electron correlation problem that is size-consistent with a size-consistent reference but fails to be regular. On the other hand, the less well-known many-body version of Brillouin-Wigner perturbation theory has the reverse properties: it is regular but fails to be size-consistent when used with the standard MP partitioning. Consequently, its widespread use remains limited. In this work, we analyze the ways in which it is possible to use alternative non-MP partitions of the Hamiltonian to yield variants of BW2 that are size-consistent as well as regular. We show that there is a vast space of such BW2 theories and also show that it is possible to define a repartitioned BW2 theory from the ground state density alone, which regenerates the exact correlation energy. We also provide a general recipe for deriving regular, size-consistent, and size-extensive partitions from physically meaningful components, and we apply the result to small model systems. The scope of these results appears to further set the stage for a revival of BW2 in quantum chemistry.

A multi-strain human skin microbiome model provides a testbed for disease modeling

The skin microbiome plays a critical role at the interface between the human epidermis and the environment, providing colonization resistance against pathogenic strains, training host immunity, and supporting epithelial turnover. Inversely, dysbiotic skin microbiome states are associated with skin disease, particularly inflammatory conditions such as atopic dermatitis and psoriasis. Current evaluation of human host and microbiome interactions relies on post hoc studies after disease onset. This limits the ability to evaluate the causal roles of host and microbe during disease progression. One approach to characterizing microbial and host biology in a controlled and reproducible context is to derive in vitro models of sufficient complexity and stability to support perturbation and response. Current tools for studying these processes are focused on testing antagonistic or synergistic relations between two or more strains for short (hours to days) culture durations, thereby precluding studies of relevant complexity and chronic disease states. Here, we present an in vitro model of the human skin microbiome comprising a six strain consortium colonizing primary human keratinocyte-derived tissue in Air-Liquid Interface for up to 7 days. We evaluated readouts of tissue health including histology, gene expression, and transepithelial electrical resistance (TEER), as well as relative strain abundance to characterize microbiome stability over time. Skin cells formed a complex tissue structure over two weeks and maintained stable or increasing TEER after 7 days of co-culture with the microbial consortium. Up to five of the six strains were viable on the skin tissue surface on day 7 as validated by custom qPCR assays, demonstrating a robust and stable testbed for microbiome studies. A remarkable feature of this model is the persistence of Cutibacterium acnes in an aerobic tissue culture environment, since C. acnes growth is typically demonstrated under anaerobic conditions, suggesting that the skin tissue model is conducive to more natural growth states of native skin strains. The addition of cytokines representative of atopic dermatitis elicited a marked decrease in tissue barrier by day 7 compared to healthy controls, irrespective of the microbiome presence. Furthermore, an alteration in relative strain abundance was observed in diseased model tissues, demonstrating capability to study the impact of disease states on the microbiome and vice versa. We envision this model system as a test bed to evaluate the influence of commensals on host biology, the influence of external environment on microbiome stability, and chronic diseases impacted by dysbiosis.

Quantitative Determination of High-Frequency Voltage Attenuation in an Electric-Pulse-Excited Stroboscopic Transmission Electron Microscope.

High-frequency electric pulse signals are often applied to stimulate functional materials in devices. To investigate the relationship between materials structure and dynamic behavior under high-frequency electric excitation, the stroboscopic imaging mode is widely used in a transmission electron microscope (TEM). From a technical point of view, it is crucial to quantitatively determine high-frequency attenuation in an electric-pulse-excited stroboscopic TEM. Here, we propose the quantitative method to evaluate the voltage attenuation by using magnification variation of defocused bright-field transmission electron microscopy images in a stroboscopic mode when applying high-frequency electric pulse signals onto a model system of two opposite tungsten tips. The negative voltage excitation possesses higher high-frequency voltage attenuation than the positive voltage excitation due to the possible nonreciprocal transmission of the triangle waves within the circuit between the biasing sample holder and the arbitrary waveform generator. Our approach of high-frequency attenuation determination provides the experimental foundation for quantitative analysis on the dynamic evolution of materials structure and functionality under electric pulse stimuli.

Research on Chinese Traditional Architectural Culture and Inheritance Strategy: A Case Study of the Goulou Cluster of Yue Dialects in Guangxi

Traditional Chinese villages and architectural cultural resources are abundant. Against the backdrop of rapid development in contemporary socioeconomic and urbanization processes, rural construction is facing multiple challenges such as imbalanced urban–rural development, gradually fading cultural traditions, and disharmonious living environments. The cultural elements of rural architecture urgently need more systematic and effective protection, integration, and reuse. Therefore, the precise extraction of traditional architectural features and their translation applications in modern contexts are gradually becoming key issues in current research and practice fields. This study takes traditional architecture of the Goulou Cluster of Yue Dialects in Guangxi, China, as an example. Through field investigations and mathematical and GIS spatial analysis, architectural samples were identified and extracted typologically, and a database of traditional architecture was constructed, delineating architectural cultural zones and summarizing type characteristics to create a genealogy map. Based on the results of the architectural genealogy study, modern translation pathways for traditional architecture were proposed through spatial modeling, technical analysis, and iterative optimization. Modern translation experiments were conducted on selected typical villages and their traditional buildings, exploring the application model system of traditional architecture in modern contexts. This study not only deepens the scientific understanding of the genealogy zoning characteristics of traditional architecture in the Goulou Cluster of Yue Dialects in Guangxi but also provides a reference for the modern translation and optimization path of traditional architecture, providing important theoretical basis and application guidance for promoting the inheritance and innovation of rural culture, and realizing the protection and updating of rural architectural style.

Live imaging of excitable axonal microdomains in ankyrin-G-GFP mice

The axon initial segment (AIS) constitutes not only the site of action potential initiation, but also a hub for activity-dependent modulation of output generation. Recent studies shedding light on AIS function used predominantly post-hoc approaches since no robust murine in vivo live reporters exist. Here, we introduce a reporter line in which the AIS is intrinsically labeled by an ankyrin-G-GFP fusion protein activated by Cre recombinase, tagging the native Ank3 gene. Using confocal, superresolution, and two-photon microscopy as well as whole-cell patch-clamp recordings in vitro, ex vivo, and in vivo, we confirm that the subcellular scaffold of the AIS and electrophysiological parameters of labeled cells remain unchanged. We further uncover rapid AIS remodeling following increased network activity in this model system, as well as highly reproducible in vivo labeling of AIS over weeks. This novel reporter line allows longitudinal studies of AIS modulation and plasticity in vivo in real-time and thus provides a unique approach to study subcellular plasticity in a broad range of applications.

Live imaging of excitable axonal microdomains in ankyrin-G-GFP mice.

The axon initial segment (AIS) constitutes not only the site of action potential initiation, but also a hub for activity-dependent modulation of output generation. Recent studies shedding light on AIS function used predominantly post-hoc approaches since no robust murine in vivo live reporters exist. Here, we introduce a reporter line in which the AIS is intrinsically labeled by an ankyrin-G-GFP fusion protein activated by Cre recombinase, tagging the native Ank3 gene. Using confocal, superresolution, and two-photon microscopy as well as whole-cell patch-clamp recordings in vitro, ex vivo, and in vivo, we confirm that the subcellular scaffold of the AIS and electrophysiological parameters of labeled cells remain unchanged. We further uncover rapid AIS remodeling following increased network activity in this model system, as well as highly reproducible in vivo labeling of AIS over weeks. This novel reporter line allows longitudinal studies of AIS modulation and plasticity in vivo in real-time and thus provides a unique approach to study subcellular plasticity in a broad range of applications.