Biology subjects

Krieg, M.

Publications and source records attributed to Krieg, M..

18 recordsLinked to original sources

bioRxiv2026

Inhomogeneous Tau polymerization, core-shell organization, and seed formation during Tau condensate aging

Several proteins aggregating in neurodegenerative diseases spontaneously segregate into liquid condensates, which can catalyze protein aggregation. How liquid-solid transitions are catalyzed in the confined condensate volume is not clear. For the microtubule associated protein Tau, aggregating intra-neuronally in Alzheimer's disease, we show that, during maturation, Tau condensates convert into elastic protein networks, accompanied by inhomogeneous polymerization of the condensate interior and the formation of high-density nodes and a 'shell'. During condensation, Tau molecules extend, favoring intermolecular interactions and priming for progressive parallel Tau arrangement that can enable amyloid-like Tau oligomerization. In cells, aged condensates seed small Tau clusters in cytosol and at the nuclear envelope, precursors of larger aggregates. By bridging molecular to condensate level, we present mechanistic insight into how Tau condensates evolve into pathological, beta-structure containing seeds. The interior of aged Tau condensates remains accessible for smaller molecules, providing the opportunity to molecularly target Tau seed formation inside condensates.

biochemistry↗

bioRxiv2026

Neural sensing of surface traction modulates proprioceptive activity and locomotion in Caenorhabditis elegans

Locomotion -- whether walking, running, or crawling -- depends on the precise coordination of forces between the body and its surroundings. Two critical factors in this process are the force that resists the relative motion between two bodies, and mechanosensation, the bodys ability to sense and respond to mechanical forces. Together, they allow organisms to move efficiently, adapt to varying environments, and maintain balance. Here we show that the gentle touch receptor neurons (TRNs) in the Caenorhabditis elegans body wall are sensitive to dynamic surface traction. Using a combination of calcium recordings and traction force microscopy in freely moving animals, microfluidics, and whole connectome computer simulations, we show that MEC-4 DEG/ENaC ion channel activity depends on the crawling velocity and friction force. Mutations disrupting MEC-4 activity and body wall mechanoreceptor function produce lethargic worms with impaired proprioceptive regulation, suggesting functional coupling between surface mechanoreceptors and proprioceptors. Our data reveal a new role for classical touch receptors in locomotion and critically define the mechanical modality sensed by skin mechanosensors.

neuroscience↗

bioRxiv2026

Bright calcium-modulated bioluminescent indicators for activity imaging and red photon-assisted synaptic transmission

Bioluminescent calcium sensors have unique uses in neuroscience and neuroengineering, enabling noninvasive imaging of neuronal activity and contactless activation of opsin-expressing neurons. However, the speed, range, and robustness of non-invasive imaging and rewiring or neuronal activity are limited by the radiance and dynamic range of existing bioluminescent calcium sensors. Here, we report the stepwise engineering of improved cyan-excitable red fluorescent proteins (mCyRFP4 and dCyRFP4), an improved red bioluminescent protein based on NanoLuc and CyRFP4 (Antares3), and an improved bioluminescent calcium sensor based on Antares3 (CaMBI3). Antares3 is 3-fold brighter than its predecessor, while CaMBI3 responds with an overall dynamic range of 24-fold, enabling high-sensitivity detection of calcium dynamics in muscle and neuronal tissues in vivo. Finally, a CaMBI3 variant and a red-shifted opsin ChRmine enabled red photon-assisted synaptic transmission in C. elegans. CaMBI3 thus facilitates genetically targeted non-invasive imaging and rewiring of neural activity in living animals.

neuroscience↗

bioRxiv2025

Seeing in the Dark: Intelligent Fourier Light Field Imaging for Bioluminescence Microscopy

Bioluminescence microscopy offers a uniquely non-invasive window into cellular dynamics, yet its use has traditionally been limited by the intrinsically low brightness of luciferases. The poor photon budget forces long exposures, preventing faithful visualization of rapid physiological processes, especially in three dimensions. To overcome this barrier, we developed a Fourier light field microscope coupled with deep learning-based reconstruction that achieves sub-second volumetric bioluminescence imaging with significantly improved spatial resolution. This approach eliminates the speed-resolution trade-off of conventional light field methods and bypasses the need for slow classical deconvolution. We demonstrate its power by performing real-time 3D calcium imaging in freely moving Caenorhabditis elegans, and by quantifying cell dynamics within stem cell- derived spheroids using fluorescently labeled nuclei and calcium dynamics in muscles and neurons. Together, these results establish our framework as a practical tool for dynamic, volumetric studies of living systems.

biophysics↗

bioRxiv2025

Periodic Obstacles Regulate Membrane Tension Propagation to Enable Localized Mechanotransduction

Forces applied to cellular membranes lead to transient membrane tension gradients. The way membrane tension propagates away from the stimulus site into the membrane reservoir is a key property in cellular adaptation. However, it remains unclear how tension propagation in membranes is regulated and how it depends on the cell type. Here, we investigate plasma membrane tension propagation in cultured Caenorhabditis elegans mechanosensory neurons. We show that tension propagation travels quickly and is restricted to a particular distance in the neurites -- projections from the cell body of a neuron. A biophysical model of tension propagation suggests that periodic obstacle density and arrangement play key roles in controlling the propagation of mechanical information. Our experiments show that tension propagation is strongly dependent on the intact actin and microtubule cytoskeleton, whereas membrane lipid properties have minimal impact. In particular, the organization of the /{beta}-spectrin network and the MEC-2 stomatin condensates in periodic scaffold act as barriers to tension propagation, limiting the spread of tension. Our findings suggest that restricting membrane tension propagation in space and time enables precise localized signaling, allows a single neuron to process mechanical signals in multiple distinct domains, thus expanding its computational capacity.

biophysics↗

bioRxiv2024

Mechanical load conditions the spectrin network to `run-on' proteolysis and promotes early onset neurodegeneration

The correct homeostasis of the neuronal cytoskeleton and its dynamics is important for health and disease. Forces constantly act on the neurons in our body, leading to subtle axonal deformations and length changes. The spectrin cytoskeleton is known as a key player that protects neurons against mechanical damage. How the spectrin cytoskeleton changes with age and how it influences mechanoprotection in aging animals is not well understood. Using an interdisciplinary approach, we show that age causes a loss of proprioception during the first few days of adulthood in C. elegans via spectrin unfolding, loss of mechanical tension and degradation of the spectrin cytoskeleton. Guided by a proteomic screen to identify potential spectrin binding partners, we found that this early-onset neurodegeneration can be suppressed in clp-1 mutants and by targeted expression of an engineered chaperone derived from human B-crystallin. Our data suggest that the spectrin cytoskeleton is sensitized to proteolytic damage by calcium-sensitive proteases when mechanical stresses conspires with high-calcium concentrations as in proprioceptive signaling. These results may have implications for the etiology of diseases in which high calcium dynamics and mechanical stress co-incide.

neuroscience↗

bioRxiv2023

Active microrheology with a single, time-shared laser trap

Recording the mechanical response of biological samples, the cells interior and complex fluids in general, would enable deeper understanding of cellular differentiation, ageing and drug discovery. Here, we present a time-shared optical tweezer microrheology (TimSOM) pipeline to determine the frequency- and age-dependent viscoelastic properties of biological materials. Our approach consists in splitting a single laser beam into two near-instantaneous time-shared optical traps to carry out simultaneous force and displacement measurements with sub-nanometer and sub-picoNewton accuracy during sinusoidal perturbations. Leveraging numerical and analytical models, we find solutions to commonly encountered deviations, to build a practical and robust nanorheometer. We demonstrate the versatility of the technique by 1) measuring the phase transitions of an ageing biomolecular condensate, 2) quantifying the complex viscoelastic properties of three intracellular compartments of zebrafish progenitor cells, and, 3) using Caenorhabditis elegans, we uncover how mutations causing nuclear envelopathies soften the cytosol of intestinal cells during organismal age. Together, our advances afford rapid phenotyping of material properties inside cells and proteins blends, opening avenues for biomedical and drug screening applications.

biophysics↗

bioRxiv2023

Integration of spatially opposing cues by a single interneuron guides decision making in C. elegans

The capacity of animals to integrate and respond to multiple hazardous stimuli in the surroundings is crucial for their survival. In mammals, complex evaluations of the environment require large numbers and different subtypes of neurons. The nematode C. elegans avoid hazardous chemicals they encounter by reversing their direction of movement. How does the worms compact nervous system processes the spatial information and directs the change of motion? We show here that a single interneuron, AVA, receives glutamatergic excitatory signals from head sensory neurons and glutamatergic inhibitory signals from the tail sensory neurons. AVA integrates the spatially distinct and opposing cues, whose output instructs the animals behavioral decision. We further find that the differential activation of AVA from the head and tail stems from distinct anatomical localization of inhibitory and excitatory glutamate-gated receptors along the AVA process, and from different threshold sensitivities of the sensory neurons to aversive stimuli. Our results thus uncover a cellular mechanism that mediates spatial computation of nociceptive cues for efficient decision-making in C. elegans.

neuroscience↗

bioRxiv2023

FLInt: Single Shot Safe Harbor Transgene Integration via Fluorescent Landmark Interference

The stable incorporation of transgenes and recombinant DNA material into the host genome is a bottleneck in many bioengineering applications. Due to the low efficiency, identifying the transgenic animals is often a needle in the haystack. Thus, optimal conditions require efficient screening procedures, but also known and safe landing sites that do not interfere with host expression, low input material and strong expression from the new locus. Here, we leverage an existing library of{approx} 300 different loci coding for fluorescent markers that are distributed over all 6 chromosomes in Caenorhabditis elegans as safe harbors for versatile transgene integration sites using CRISPR/Cas9. We demonstrated that a single crRNA was sufficient for cleavage of the target region and integration of the transgene of interest, which can be easily followed by loss of the fluorescent marker. The same loci can also be used for extrachromosomal landing sites and as co-CRISPR markers without affecting body morphology or animal behavior. Thus, our method overcomes the uncertainty of transgene location during random mutagenesis, facilitates easy screening through fluorescence interference and can be used as co-CRISPR markers without further influence in phenotypes.

genetics↗

bioRxiv2022

A rigidity phase transition of Stomatin condensates governs a switch from transport to mechanotransduction

A large body of work suggests that biomolecular condensates ensuing from liquid-liquid phase separation mature into various material states. How this aging process is controlled and if the naive and mature phases can have differential functions is currently unknown. Using Caenorhabditis elegans as a model, we show that MEC-2 Stomatin undergoes a rigidity phase transition during maturation from fluid to viscoelastic, glass-like condensates that facilitate either transport or mechanotransduction. This switch is promoted by the SH3 domain of UNC-89/Titin/Obscurin through a direct interaction with MEC-2 and suggests a physiological role for a percolation transition in force transmission during body wall touch. Together, our data demonstrate a novel function for rigidity maturation during mechanotransduction and a previously unidentified role for Titin homologs in neurons.

cell biology↗

bioRxiv2022

Volumetric bioluminescence imaging of cellular dynamics with deep learning based light-field reconstruction

The application of genetically encoded fluorophores for microscopy has afforded one of the biggest revolutions in the biosciences. Bioluminescence microscopy is an appealing alternative to fluorescence microscopy, because it does not depend on external illumination, and consequently does neither produce spurious background autofluorescence, nor perturb intrinsically photosensitive processes in living cells and animals. The low quantum yield of known luciferases, however, limit the acquisition of high signal-noise images of fast biological dynamics. To increase the versatility of bioluminescence microscopy, we present an improved low-light microscope in combination with deep learning methods to increase the signal to noise ratio in extremely photon-starved samples at millisecond exposures for timelapse and volumetric imaging. We apply our method to image subcellular dynamics in mouse embryonic stem cells, the epithelial morphology during zebrafish development, and DAF-16 FoxO transcription factor shuttling from the cytoplasm to the nucleus under external stress. Finally, we concatenate neural networks for denoising and light-field deconvolution to resolve intracellular calcium dynamics in three dimensions of freely moving Caenorhabditis elegans with millisecond exposure times. This technology is cost-effective and has the potential to replace standard optical microscopy where external illumination is prohibitive.

bioengineering↗

bioRxiv2022

Axonal plasticity in response to active forces generated through magnetic nano-pulling

Mechanical force is crucial in guiding axon outgrowth, before and after synapse formation. This process is referred to as "stretch-growth". However, how neurons transduce mechanical inputs into signaling pathways remains poorly understood. Another open question is how stretch-growth is coupled in time with the intercalated addition of new mass along the entire axon. Here, we demonstrate that active mechanical force generated by magnetic nano-pulling induces a remodeling of the axonal cytoskeleton. Specifically, the increase in the axonal density of microtubules leads to an accumulation of organelles and signaling vesicles which, in turn, promotes local translation by increasing the probability of assembly of the "translation factories". The modulation of axonal transport and local translation sustains enhanced axon outgrowth and synapse maturation.

neuroscience↗

bioRxiv2022

Sexually dimorphic architecture and function of a mechanosensory circuit in C. elegans

How sensory perception is processed by the two sexes of an organism is still only partially understood. Despite some evidence for sexual dimorphism in auditory and olfactory perception, whether touch is sensed in a dimorphic manner has not been addressed. Here we find that the neuronal circuit for tail mechanosensation in C. elegans is wired differently in the two sexes and employs a different combination of sex-shared sensory neurons and interneurons in each sex. Reverse genetic screens uncovered cell- and sex-specific functions of the alpha-tubulin mec-12 and the sodium channel tmc-1 in sensory neurons, and of the glutamate receptors nmr-1 and glr-1 in interneurons, revealing the underlying molecular mechanisms that mediate tail mechanosensation. Moreover, we show that only in males, the sex-shared interneuron AVG is strongly activated by tail mechanical stimulation, and accordingly is crucial for their behavioral response. Importantly, sex reversal experiments demonstrate that the sexual identity of AVG determines both the behavioral output of the mechanosensory response and the molecular pathways controlling it. Our results present for the first time extensive sexual dimorphism in a mechanosensory circuit at both the cellular and molecular levels.

neuroscience↗

bioRxiv2021

Deploying photons for communication within neuronal networks

Deficiencies in neurotransmission lead to neurological disorders or misinterpretation of perceived threats. To restore defects in cellular communication, we developed a synthetic, photon-assisted synaptic transmission (PhAST) system. PhAST is based on luciferases and channelrhodopsins that enable the transmission of a neuronal state across space, using photons as neurotransmitters. We demonstrate the ability to overcome synaptic barriers and rescue the behavioral deficit of a genetically engineered glutamate mutant with conditional, Ca2+-triggered photon emission between two cognate neurons of the Caenorhabditis elegans nociceptive avoidance circuit. We also deploy these ingredients for asynaptic transmission between two unrelated cells in a sexually dimorphic neuronal network. Functional PhAST could sensitize otherwise poorly responsive males to touch and hence expand the behavioral repertoire. Our study, thus, establishes a powerful framework for complex photon-based communication between neurons in a living animal, that can readily be expanded to synthetic neuronal networks, organoids or non-invasive brain-machine interfaces.

synthetic biology↗

bioRxiv2021

Mechanical Stretch Inhibition SensitizesProprioceptors to Compressive Stresses

A repetitive gait cycle is an archetypical component within the behavioural repertoire of many if not all animals including humans. It originates from mechanical feedback within proprioceptors to adjust the motorprogram during locomotion and thus leads to a periodic orbit in a low dimensional space. Here, we investigate the mechanics, molecules and neurons responsible for proprioception in Caenorhabditis (C.) elegans to gain insight into how mechanosensation shapes the orbital trajectory to a well-defined limit cycle. We used genome editing, force spectroscopy and multiscale modeling and found that alternating tension and compression with the spectrin network of a single proprioceptor encodes body posture and informs TRP-4/NOMPC and TWK-16/TREK2 homologs of mechanosensitive ion channels during locomotion. In contrast to a widely accepted model of proprioceptive stretch reception, we found that proprioceptors activated under compressive stresses in vivo and in vitro, and speculate that this property is conserved across function and species.

neuroscience↗

bioRxiv2019

The nucleus measures shape deformation for cellular proprioception and regulates adaptive morphodynamics

The physical microenvironment regulates cell behavior during tissue development and homeostasis. How single cells decode information about their geometrical shape under mechanical stress and physical space constraints within their local environment remains largely unknown. Here we show that the nucleus, the biggest cellular organelle, functions as a non-dissipative cellular shape deformation gauge that enables cells to continuously measure shape variations on the time scale of seconds. Inner nuclear membrane unfolding together with the relative spatial intracellular positioning of the nucleus provides physical information on the amplitude and type of cellular shape deformation. This adaptively activates a calcium-dependent mechano-transduction pathway, controlling the level of actomyosin contractility and migration plasticity. Our data support that the nucleus establishes a functional module for cellular proprioception that enables cells to sense shape variations for adapting cellular behaviour to their microenvironment. One Sentence SummaryThe nucleus functions as an active deformation sensor that enables cells to adapt their behavior to the tissue microenvironment.

cell biology↗

bioRxiv2019

Cortical anchoring of the microtubule cytoskeleton is essential for neuron polarity and functioning

Neurons are among the most highly polarized cell types. They possess structurally and functionally different processes, axon and dendrites, to mediate information flow through the nervous system. Although it is well known that the microtubule cytoskeleton has a central role in establishing neuronal polarity, how its specific organization is established and maintained is little understood.\n\nUsing the in vivo model system Caenorhabditis elegans, we found that the highly conserved UNC-119 protein provides a link between the membrane-associated Ankyrin (UNC-44) and the microtubule-associated CRMP (UNC-33). Together they form a periodic membrane-associated complex that anchors axonal and dendritic microtubule bundles to the cell cortex. This anchoring is critical to maintain microtubule organization by opposing kinesin-1 powered microtubule sliding. Disturbing this molecular complex alters neuronal polarity and causes strong developmental defects of the nervous system leading to severely paralyzed animals.

cell biology↗

bioRxiv2018

Proprioceptive neurons of larval Drosophila melanogaster show direction selective activity requiring the mechanosensory channel TMC.

Drosophila Transmembrane channel-like (Tmc) is a protein that functions in larval proprioception. The closely related TMC1 protein is required for mammalian hearing, and is a pore forming subunit of the hair cell mechanotransduction channel. In hair cells, TMC1 is gated by small deflections of microvilli that produce tension on extracellular tip-links that connect adjacent villi. How Tmc might be gated in larval proprioceptors, which are neurons having a morphology that is completely distinct from hair cells, is unknown. Here, we have used high-speed confocal microscopy to both measure displacements of proprioceptive sensory dendrites during larval movement, and to optically measure neural activity of the moving proprioceptors. Unexpectedly, the pattern of dendrite deformation for distinct neurons was unique and differed depending on the direction of locomotion: ddaE neuron dendrites were strongly curved by forward locomotion while the dendrites of ddaD were more strongly deformed by backward locomotion. Furthermore, GCaMP6f calcium signals recorded in the proprioceptive neurons during locomotion indicated tuning to the direction of movement. ddaE showed strong activation during forward locomotion while ddaD showed responses that were strongest during backwards locomotion. Peripheral proprioceptive neurons in animals mutant for Tmc showed a near complete loss of movement related calcium signals. As the strength of the responses of wild type animals was correlated with dendrite curvature, we propose that Tmc channels may be activated by membrane curvature in dendrites that are exposed to strain. Our findings begin to explain how distinct cellular systems rely on a common molecular pathway for mechanosensory responses.

neuroscience↗