Biology subjects

Kühn, S.

Publications and source records attributed to Kühn, S..

11 recordsLinked to original sources

bioRxiv2025

A high-affinity split-HaloTag for live-cell protein labeling

We introduce a high-affinity split-HaloTag comprised of a short peptide tag (Hpep, 14 residues) and a large, inactive fragment (cpHalo{Delta}3). Hpep binds to cpHalo{Delta}3 spontaneously with nanomolar affinity, enabling subsequent labeling with fluorescent HaloTag ligands. The small size of Hpep facilitates cloning-free endogenous protein tagging using CRISPR/Cas9 and the complementation of Hpep-tagged proteins can be achieved in live cells through co-expression with cpHalo{Delta}3 and in fixed cells through incubation with cpHalo{Delta}3. The approach is compatible with advanced microscopy techniques such as expansion microscopy and live-cell STED imaging. Additionally, variants of Hpep that modulate the spectral properties of labeled fluorophores enable simultaneous imaging of two different Hpep-tagged proteins via fluorescence lifetime microscopy. In summary, our high-affinity split-HaloTag is a robust and versatile tool for live-cell imaging and diverse applications in chemical biology.

biochemistry↗

bioRxiv2025

Distinguishing Lifelong Individual Differences from Divergent Aging Trajectories of Adult Brain Volumes

Individual differences in the volumes of brain structures are often linked to various conditions, including Alzheimers disease, schizophrenia, and overall brain health. However, it remains unclear to what extent these differences reflect individual levels present from young adulthood or diverging aging trajectories from later ages. In this study, we analyze the aging dynamics of the volumes of six brain structures based on magnetic resonance imaging (MRI) scans from a large cross-cohort longitudinal sample of cognitively healthy adults (n = 8,311 with 18,520 MRIs, ages from 18 to 97 years). From general assumptions about structural brain dynamics and measurement noise, a stochastic dynamical model was fitted to the data to estimate both the variability and persistence of structural changes across adulthood. Using this model, we calculated how much of the variance of volumetric differences between individuals can be attributed to stable levels from young adulthood versus systematic changes at older ages, as well as the theoretical sensitivity of longitudinal studies to detect individual differences in change. The findings were as follows: 1) Before age 60 years, inter-individual differences in neuroanatomical volumes almost exclusively reflect stable differences between individuals, while the influence from systematic differences in rate-of-change increases thereafter; up to 50 % of the variation being due to differences in change at 80 years. In contrast, ventricular volume reflects differences in change from early adulthood. 2) Current brain-age models are unlikely to be sensitive to detect differences in aging trajectories. 3) Imaging studies have low reliability in detecting inter-individual brain changes before age 60. After 60 years, the study reliability increases sharply with longer intervals between scans and more modestly with additional intermediate observations. In conclusion, our results reinforce the view that it is critical to distinguish stable early-adulthood levels from systematic differences in change when studying adult brain aging.

neuroscience↗

bioRxiv2024

SNAP-tag2: faster and brighter protein labeling

SNAP-tag is a powerful tool for labeling proteins with synthetic fluorophores in bioimaging. However, its utility in live-cell applications can be constrained by its relatively slow labeling kinetics and the limited cell permeability of its substrates. Here we introduce new labeling substrates and an engineered SNAP-tag for faster labeling in vitro and in live cells. SNAP-tag2 presents a second-order rate constant with rhodamine substrates that approaches 107 s-1 M-1, a 100-fold improvement over the corresponding SNAP-tag-substrate pairs. When labeled with highly fluorogenic dyes, SNAP-tag2 also shows a 5-fold increase in fluorescence brightness relative to currently used SNAP-tag. The increased labeling kinetics and brightness of SNAP-tag2 translates into a greatly improved performance in various live-cell (super-resolution) imaging applications.

biochemistry↗

bioRxiv2022

Neural correlates of an illusive sense of agency caused by virtual reality

Sense of agency (SoA) is the sensation that self-actions lead to ensuing perceptual consequences. The prospective mechanism emphasizes that SoA arises from motor prediction and its comparison with actual action outcomes, while the reconstructive mechanism stresses that SoA emerges from retrospective causal processing about the action outcomes. Consistent with the prospective mechanism, motor planning regions were identified by neuroimaging studies using the temporal binding effect, a behavioral measure often linked to implicit SoA. Yet, temporal binding also occurs during passive observation of anothers action, lending support to the reconstructive mechanism, but its neural correlates remain unexplored. Here, we employed virtual reality (VR) to modulate such observation-based SoA and examined it with functional magnetic resonance imaging. After manipulating an avatar hand in VR, participants passively observed an avatars "action" and showed a significant increase in temporal binding. The binding effect was associated with the right angular gyrus and inferior parietal lobule, which are critical nodes for inferential and agency processing. These results suggest that the experience of controlling an avatar may potentiate inferential processing within the right inferior parietal cortex and give rise to the illusionary sense of agency without voluntary action.

neuroscience↗

bioRxiv2021

Limited metacognitive access to one's own facial expressions

As humans we communicate important information through fine nuances in our facial expressions, but because conscious motor representations are noisy, we might not be able to report these fine but meaningful movements. Here we measured how much explicit metacognitive information young adults have about their own facial expressions. Participants imitated pictures of themselves making facial expressions and triggered a camera to take a picture of them while doing so. They then rated confidence (how well they thought they imitated each expression). We defined metacognitive access to facial expressions as the relationship between objective performance (how well the two pictures matched) and subjective confidence ratings. Metacognitive access to facial expressions was very poor when we considered all face features indiscriminately. Instead, machine learning analyses revealed that participants rated confidence based on idiosyncratic subsets of features. We conclude that metacognitive access to own facial expressions is partial, and surprisingly limited.

neuroscience↗

bioRxiv2020

Observing plasticity of the auditory system: Volumetric decreases along with increased functional connectivity in aspiring professional musicians

Playing music relies on several sensory systems and the motor system, and poses strong demands on control processes, hence, offering an excellent model to study how experience can mold brain structure and function. While most studies on neural correlates of music expertise rely on cross-sectional comparisons, here we compared within-person changes over time in aspiring professionals intensely preparing for an entrance exam at a University of the Arts to skilled amateur musicians not preparing for a music exam. In the group of aspiring professionals, we observed gray-matter volume decrements in left planum polare, posterior insula, and left inferior frontal orbital gyrus over a period of about six months that were absent among the amateur musicians. At the same time, the left planum polare, the largest cluster of structural change, showed increasing functional connectivity with left and right auditory cortex, left precentral gyrus, left supplementary motor cortex, left and right postcentral gyrus, and left cingulate cortex, all regions previously identified to relate to music expertise. In line with the expansion-renormalization pattern of brain plasticity (Wenger, Brozzoli, et al. 2017), the aspiring professionals might have been in the selection and refinement period of plastic change.

neuroscience↗

bioRxiv2020

Durable memories and efficient neural coding through mnemonic training using the method of loci

Mnemonic techniques, such as the method of loci, can powerfully boost memory. Here, we compared memory athletes ranked among the worlds top 50 in memory sports to mnemonics-naive controls. In a second study, participants completed a six-weeks memory training, working memory training, or no intervention. Behaviorally, memory training enhanced durable, longer-lasting memories. fMRI during encoding and recognition revealed task-based activation decreases in lateral prefrontal, as well as in parahippocampal and retrosplenial cortices in both memory athletes and participants after memory training, partly associated with better performance after four months. This was complemented by hippocampal-neocortical coupling during consolidation, which was stronger the more durable memories participants formed. Our findings are the first to demonstrate that mnemonic training boosts durable memory formation via decreased task-based activation and increased consolidation thereafter. This is in line with conceptual accounts of neural efficiency and highlights a complex interplay of neural processes critical for extraordinary memory.

neuroscience↗

bioRxiv2020

A new form of actin assembly around the Shigella-containing vacuole regulates its intracellular niche

The enteroinvasive bacterium Shigella flexneri forces its uptake into non-phagocytic host cells through the translocation of T3SS effectors that subvert the actin cytoskeleton. Here, we report de novo actin polymerization after cellular entry around the bacterial containing vacuole (BCV) leading to the formation of a dynamic actin cocoon. This cocoon is thicker than any described cellular actin structure and functions as a gatekeeper for the cytosolic access of the pathogen. Host Cdc42, Toca-1, N-WASP, WIP, the Arp2/3 complex, cortactin, coronin, and cofilin are recruited to the actin cocoon. They are subverted by T3SS effectors, such as IpgD, IpgB1, and IcsB. IcsB immobilizes components of the actin polymerization machinery at the BCV. This represents a novel microbial subversion strategy through localized entrapment of host actin regulators causing massive actin assembly. We propose that the cocoon protects Shigellas niche from canonical maturation or host recognition.

cell biology↗

bioRxiv2019

Hippocampal subfields and limbic white matter jointly predict learning rate in older adults

Age-related memory impairments have been linked to differences in structural brain parameters, including cerebral white matter (WM) microstructure and hippocampal (HC) volume, but their combined influences are rarely investigated. In a population-based sample of 337 older participants 61-82 years of age (Mage=69.66, SDage=3.92 years) we modeled the independent and joint effects of limbic WM microstructure and HC subfield volumes on verbal learning. Participants completed a verbal learning task over five learning trials and underwent magnetic resonance imaging (MRI), including structural and diffusion scans. We segmented three HC subregions on high-resolution MRI data and sampled mean fractional anisotropy (FA) from bilateral limbic WM tracts identified via deterministic fiber tractography. Using structural equation modeling, we evaluated the associations between learning rate and latent factors representing FA sampled from limbic WM tracts, and HC subfield volumes, as well as their latent interaction. Results showed limbic WM and the interaction of HC and WM - but not HC volume alone - predicted verbal learning rates. Model decomposition revealed HC volume is only positively associated with learning rate in individuals with higher levels of WM anisotropy. We conclude that structural characteristics of limbic WM regions and HC volume jointly contribute to verbal learning in older adults.

neuroscience↗

bioRxiv2018

Evaluation of FlowVR: a virtual reality game for improvement of depressive mood

ObjectiveThis study evaluated the efficacy of FlowVR, a virtual reality (VR) game designed to improve mood and reduce feelings of depression. The aim is to contribute to the question of whether and how VR could be used for depression therapy, as research in this area is quite rare.\n\nMethod18 healthy participants (9 female; Mage = 25.9) underwent three conditions, playing FlowVR in VR with a head-mounted display, playing FlowVR on a tablet or reading a text on a tablet. For each condition, they were tested on a separate day at the same time of day within a two-week period. Before and after every condition participants completed the Becks Depression Inventory II (BDI-II), the state part of the State-Trait-Anxiety-Depression-Inventory (STADI(S)) and the Positive Affect Negative Affect Schedule-Expanded Form (PANAS-X).\n\nResultsWhile the participants showed only a reduction in acute anxiety in the control and the tablet conditions, they showed improved affectivity in all variables measured in the VR condition. In addition, VR had significantly better results than the control condition in improving positive affectivity, negative affectivity and acute feelings of depression. Using a less conservative statistical approach, these significant differences could also be found between the tablet and the VR condition. There were no significant differences between the tablet and the control condition.\n\nConclusionThe results indicate that due to its immersive nature, VR can be used effectively to improve mood and temporarily reduce feelings of depression. Long-term effects of FlowVR on participants with depression must be investigated in consecutive research.

neuroscience↗

bioRxiv2018

Variability and reliability of effective connectivity within the core default mode network: A longitudinal spectral DCM study

Dynamic causal modelling (DCM) for resting state fMRI - namely spectral DCM - is a recently developed and widely adopted method for inferring effective connectivity in intrinsic brain networks. Most research applying spectral DCM has focused on group-averaged connectivity within large-scale intrinsic brain networks; however, the consistency of subject- and session-specific estimates of effective connectivity has not been evaluated. Establishing reliability (within subjects) is crucial for its clinical use; e.g., as a neurophysiological phenotype of disease progression. Effective connectivity during rest is likely to vary due to changes in cognitive, behavioural, and physical states. Determining the sources of fluctuations in effective connectivity may yield greater understanding of brain processes and inform clinical applications about potential confounds. In the present study, we investigated the consistency of effective connectivity within and between subjects, as well as potential sources of variability (e.g., hemispheric asymmetry). We further investigated how standard procedures for data processing and signal extraction affect this consistency. DCM analyses were applied to four longitudinal resting state fMRI datasets. Our sample consisted of 20 subjects with 653 resting state fMRI sessions in total. These data allowed to quantify the robustness of connectivity estimates for each subject, and to draw conclusions beyond specific data features. We found that subjects contributing to all datasets showed systematic and reliable patterns of hemispheric asymmetry. When asymmetry was taken into account, subjects showed very similar connectivity patterns. We also found that various processing procedures (e.g. global signal regression and ROI size) had little effect on inference and reliability of connectivity for the majority of subjects. Bayesian model reduction increased reliability (within-subjects) and stability (between-subjects) of connectivity patterns.

neuroscience↗