Biology subjects

Giniger, E.

Publications and source records attributed to Giniger, E..

10 recordsLinked to original sources

bioRxiv2025

Nanotopographic Control of Actin Waves and Growth Cone Navigation in Developing Neurons

The development of axons and dendrites (neurites) in a neural circuit relies on the dynamic interplay of cytoskeletal components, especially actin, and the integration of diverse environmental cues. Building on prior findings that actin dynamics can serve as a primary sensor of physical guidance cues, this work investigates the role of nanotopography in modulating and guiding actin waves and neurite-tip dynamics during early neural circuit development. Although actin dynamics is well known to contribute to pathfinding in wide axonal tips, typically referred to as growth cones, we also observe dynamic actin remodeling throughout neurites and at other, narrower, neurite tips. We find that actin-wave speeds do not change significantly in the first two weeks of neurite development on flat substrates, but decrease over the same period in neurites on nanoridges. The ability of nanoridges to guide actin waves and the neurite-tip direction also decreases as neurites mature, both for narrow tips and wide growth cones. This change in responsiveness to physical guidance cues with neuronal maturation may impact the regenerative capacity of developing neural cells that are inserted into mature brains.

biophysics↗

bioRxiv2024

MANIPULATING MITOCHONDRIAL REACTIVE OXYGEN SPECIES ALTERS SURVIVAL IN UNEXPECTED WAYS IN A DROSOPHILA MODEL OF NEURODEGENERATION

Reactive oxygen species (ROS) are associated with aging and neurodegeneration, but the significance of this association remains obscure. Here, using a Drosophila model of age-related neurodegeneration, we probe this relationship in the pathologically relevant tissue, the brain, by quantifying three specific mitochondrial ROS and manipulating these redox species pharmacologically. Our goal is to ask whether pathology-associated changes in redox state are detrimental for survival, whether they may be beneficial responses, or whether they are simply covariates of pathology that do not alter viability. We find, surprisingly, that increasing mitochondrial H2O2 correlates with improved survival. We also find evidence that drugs that alter the mitochondrial glutathione redox potential modulate survival primarily through the compensatory effects they induce rather than through their direct effects on the final mitochondrial glutathione redox potential per se. We also find that the response to treatment with a redox-altering drug varies dramatically depending on the age at which the drug is administered, the duration of the treatment, and the genotype of the individual receiving the drug. These data have important implications for the design and interpretation of studies investigating the effect of redox state on health and disease as well as on efforts to modify the redox state to achieve therapeutic goals.

neuroscience↗

bioRxiv2024

Changes in mitochondrial distribution occur at the axon initial segment in association with neurodegeneration in Drosophila

Changes in mitochondrial distribution are a feature of numerous age-related neurodegenerative diseases. In Drosophila, reducing the activity of Cdk5 causes a neurodegenerative phenotype and is known to affect several mitochondrial properties. Therefore, we investigated whether alterations of mitochondrial distribution are involved in Cdk5-associated neurodegeneration. We find that reducing Cdk5 activity does not alter the balance of mitochondrial localization to the somatodendritic vs. axonal neuronal compartments of the mushroom body, the learning and memory center of the Drosophila brain. We do, however, observe changes in mitochondrial distribution at the axon initial segment (AIS), a neuronal compartment located in the proximal axon involved in neuronal polarization and action potential initiation. Specifically, we observe that mitochondria are partially excluded from the AIS in wild-type neurons, but that this exclusion is lost upon reduction of Cdk5 activity, concomitant with the shrinkage of the AIS domain that is known to occur in this condition. This mitochondrial redistribution into the AIS is not likely due to the shortening of the AIS domain itself but rather due to altered Cdk5 activity. Furthermore, mitochondrial redistribution into the AIS is unlikely to be an early driver of neurodegeneration in the context of reduced Cdk5 activity. Summary statementIn Drosophila, mitochondria are excluded from the axon iniCal segment, a neuronal compartment that regulates neuron polarity and axon potenCals, and this paYern is disrupted in a model of neurodegeneraCon.

neuroscience↗

bioRxiv2022

Enabled primarily controls filopodial morphology, not actin organization, in the TSM1 growth cone in Drosophila

Ena/VASP proteins are processive actin polymerases that are required throughout animal phylogeny for many morphogenetic processes, including axon growth and guidance. Here we use live imaging of morphology and actin organization in the TSM1 axon of the Drosophila wing to dissect the mechanism of Ena action. We find that altering Ena activity has a substantial impact on filopodial morphology in this growth cone, but exerts only modest effects on actin organization. This is in contrast to the main regulator of Ena, Abl tyrosine kinase, which has profound effects on actin and only mild effects on TSM1 growth cone morphology. These data suggest that the primary role of Ena in this axon may be to link actin to morphogenetic processes of the plasma membrane, rather than regulating actin organization itself. These data also suggest that a key role of Ena, acting downstream of Abl, may be to maintain a constant filopodial organization of the growth cone, even as Abl activity varies in response to guidance cues in the environment. Summary statementWe dissect the function of the actin polymerase, Enabled, in axon growth by live-imaging of actin dynamics and axon morphology of the TSM1 neuron in its native environment in vivo.

neuroscience↗

bioRxiv2021

Computational simulations reveal that Abl activity controls cohesiveness of actin networks in growth cones

Extensive studies of growing axons have revealed many individual components and protein interactions that guide neuronal morphogenesis. Despite this, however, we lack any clear picture of the emergent mechanism by which this nanometer-scale biochemistry generates the multi-micron scale morphology and cell biology of axon growth and guidance in vivo. To address this, we studied the downstream effects of the Abl signaling pathway using a computer simulation software (MEDYAN) that accounts for mechanochemical dynamics of active polymers. Previous studies implicate two Abl effectors, Arp2/3 and Enabled, in Abl-dependent axon guidance decisions. We now find that Abl alters actin architecture primarily by activating Arp2/3, while Enabled plays a more limited role. Our simulations show that simulations mimicking modest levels of Abl activity bear striking similarity to actin profiles obtained experimentally from live-imaging of actin in wild type axons in vivo. Using a graph-theoretical filament-filament contact analysis, moreover, we find that networks mimicking hyperactivity of Abl (enhanced Arp2/3) are fragmented into smaller domains of actin that interact weakly with each other, consistent with the pattern of actin fragmentation observed upon Abl overexpression in vivo. Two perturbative simulations further confirm that high Arp2/3 actin networks are mechanically disconnected and fail to mount a cohesive response to perturbation. Taken together, these data provide a molecular-level picture of how the large-scale organization of the axonal cytoskeleton arises from the biophysics of actin networks. Highlight summaryHow do single-molecule dynamics produce multi-micron scale changes in actin organization in an extending axon? Comparison of computational simulations to in vivo data suggests that Abl kinase and Arp2/3 expand actomyosin networks by fragmenting into multiple domains, thus toggling the axon between states of local vs global internal connectivity.

cell biology↗

bioRxiv2021

Notch-dependent Abl signaling regulates cell motility during ommatidial rotation in Drosophila

A collective cell motility event that occurs during Drosophila eye development, ommatidial rotation (OR), serves as a paradigm for signaling pathway-regulated directed movement of cell clusters. OR is instructed by several signaling events, including the EGFR and Notch pathways, and planar cell polarity (PCP) signaling, all of which are associated with photoreceptor R3 and R4 specification and differentiation. Here, we show that Abl kinase negatively regulates ommatidial rotation through its activity in the R3/R4 pair. Interestingly in wild-type, Abl is localized to apical junctional regions in R4 but not in R3 during OR, and this apical enrichment requires Notch signaling. We further demonstrate that Abl and Notch genetically interact during OR, and Abl co-immunoprecipitates in complexes with Notch in the developing eye disc. Perturbations of Abl interfere with adherens junction dynamics of the ommatidial preclusters, which are critical for the OR process. Taken together, our data suggest a model in which Abl kinase acts directly downstream of the Notch receptor in R4 to fine-tune OR via its input into adherens junction complexes.

developmental biology↗

bioRxiv2020

A polymer gel index-matched to water enables diverse applications in fluorescence microscopy

We demonstrate diffraction-limited and super-resolution imaging through thick layers (tens-hundreds of microns) of BIO-133, a biocompatible, UV-curable, commercially available polymer with a refractive index (RI) matched to water. We show that cells can be directly grown on BIO-133 substrates without the need for surface passivation and use this capability to perform extended time-lapse volumetric imaging of cellular dynamics 1) at isotropic resolution using dual-view light-sheet microscopy, and 2) at super-resolution using instant structured illumination microscopy. BIO-133 also enables immobilization of 1) Drosophila tissue, allowing us to track membrane puncta in pioneer neurons, and 2) Caenorhabditis elegans, which allows us to image and inspect fine neural structure and to track pan-neuronal calcium activity over hundreds of volumes. Finally, BIO-133 is compatible with other microfluidic materials, enabling optical and chemical perturbation of immobilized samples, as we demonstrate by performing drug and optogenetic stimulation on cells and C. elegans.

bioengineering↗

bioRxiv2019

HTT is a repressor of ABL activity required for APP induced axonal growth

ABL tyrosine kinase activity controls several aspects of development including axon patterning. Amyloid precursor protein (APP) is linked to Alzheimers disease and previous work established that ABL is a downstream effector in an Appl, the Drosophila App ortholog, signaling pathway which modulates axon outgrowth in the mushroom bodies (MBs), the fly memory center. Here we show that Abl is required for the MB neuron axonal growth. Importantly, both Abl overexpression and lack of expression produce a similar phenotype in the MBs indicating the necessity of tightly regulating ABL activity. We find that the fly huntingtin protein (HTT), the homolog of the protein involved in Huntingtons disease, behaves genetically as a repressor of ABL activity. Supporting this, FRET-based measurements of in vivo ABL activity in the MBs reveal a clear increase in its activity when HTT levels are reduced. Thus, in addition to its many other reported roles, HTT acts as a negative regulator of ABL activity, at least in the MBs, to maintain its appropriate physiological levels necessary for axon growth.

neuroscience↗

bioRxiv2019

Abl signaling shapes the intrinsic fluctuations of actin to direct growth of a pioneer axon in Drosophila

The fundamental problem in axon growth and guidance is to understand how cytoplasmic signaling modulates the cytoskeleton to produce directed growth cone motility. We show here that the TSM1 pioneer axon of Drosophila extends by using Abl tyrosine kinase to shape the intrinsic fluctuations of a mass of accumulated actin in the distal axon. The actin mass fluctuates stochastically in length, but with a small, forward bias that drives the axon along its trajectory by promoting emergence of protrusions in leading intervals where actin accumulates, and collapse of protrusions in lagging intervals that actin has vacated. The actin mass is sculpted by Abl signaling, which probabilistically modulates its key parameters - its width and internal disorder - to drive its advance, while maintaining internal coherence. Comparison of TSM1 to other systems suggests that the mechanism we demonstrate here is apt to be common among pioneer axons in many organisms.

cell biology↗

bioRxiv2018

Long-range Notch-mediated tissue patterning requires actomyosin contractility

Dynamic, actin-based protrusions function in cell-cell signaling in a variety of systems. In the dorsal thorax of the developing fly, basal protrusions enable non-neighboring epithelial cells to touch, extending the range over which Notch-mediated lateral inhibition can occur during bristle patterning. Given that actin-based cell protrusions can exert mechanical forces on their environment and Notch receptor activation is mechanically sensitive, how might cytoskeletal contractility contribute to Notch signaling? We identify a pool of basal non-muscle myosin II (myosin II) that regulates protrusion dynamics, promotes Notch signaling, and is required in signal sending and receiving cells for Notch-dependent patterning. We show that interactions between protrusions are extensive and subject to actomyosin contractility. The effects of reducing myosin II activity are more pronounced for protrusion-mediated signaling than for signaling at lateral cell contacts. Together, these results reveal a role for actomyosin contractility in Notch activation, signaling, and patterning in a developmental context.

developmental biology↗