Biology subjects

Iwanski, M. K.

Publications and source records attributed to Iwanski, M. K..

7 recordsLinked to original sources

bioRxiv2025

Polarity reversal of stable microtubules during neuronal development

Neurons critically depend on long-distance transport orchestrated by motor proteins walking over their highly asymmetric microtubule cytoskeleton. These microtubules are organized uniformly in axons with their plus-end pointing away from the soma. In contrast, in the dendrites of vertebrate neurons, microtubules are of mixed polarity, but organized into bundles of uniform polarity with stable, long-lived microtubules preferentially oriented minus-end-out and dynamic microtubules oriented plus-end-out. This organization is thought to be essential for guiding selective transport into dendrites, yet how this organization is established is unclear. Here we use a combination of single molecule localization microscopy, expansion microscopy, and live-cell imaging to examine how the microtubule cytoskeleton is reorganized during neuronal development of cultured rat hippocampal neurons. We find that, while the youngest neurites contain microtubules of mixed polarity, stable microtubules are initially preferentially oriented plus-end-out. At this stage of development many stable microtubules are connected to the centrioles, providing an explanation for their plus-end out orientation in emerging neurites. In later stages, these microtubules are released from the centrioles and reorient by sliding between or within neurites to become progressively more minus-end-out. Moreover, prior to axon specification, we commonly observed already one or two minor neurites with an almost uniformly plus-end-out microtubule network, indicative of transient polarization. Together, our findings reveal how stable microtubules are reorganized to help establish the stereotypical microtubule networks seen in the axon and dendrites of mature vertebrate neurons.

cell biology↗

bioRxiv2024

Small molecule-directed differentiation of submerged-cultured human nasal airway epithelia for respiratory disease modelling

Submerged cultures of undifferentiated or transformed epithelial cells are widely used in respiratory research due to their ease of use and scalability. However, these systems fail to capture the cellular diversity of the human airway epithelium. In this study, we developed an in vitro model where cryopreserved human nasal epithelial cells, collected by brushings, are differentiated under submerged conditions on standard plastic cultureware. By applying small-molecule inhibitors targeting Notch and BMP signaling, we achieved efficient differentiation of cultures containing basal, secretory, and ciliated cells. This approach supports scalable culturing of both 2D epithelial monolayers and 3D organoids, validated as (personalized) disease models for primary ciliary dyskinesia, cystic fibrosis, and respiratory syncytial virus infection. This model offers a cost-effective, scalable platform that combines the simplicity of traditional cultures with the cellular complexity of the human airway epithelium, providing a valuable tool for respiratory disease research.

cell biology↗

bioRxiv2024

Aurora B controls microtubule stability to regulate abscission dynamics in stem cells

Abscission is the last step of cell division leading to the complete separation of the two sister cells and consists of the cutting of a cytoplasmic bridge. Abscission is mediated by the ESCRT membrane remodeling machinery which also triggers the severing of a thick bundle of microtubules that needs to be cleared prior to abscission. Here, we show that rather than being passive actors in abscission, microtubules control abscission speed. Using mouse embryonic stem cells, which transition from slow to fast abscission during exit from naive pluripotency, we investigate the molecular mechanism for the regulation of abscission dynamics and identify a feedback loop between the activity of Aurora B and microtubule stability. We demonstrate that naive stem cells maintain high Aurora B activity after cytokinesis. This high Aurora B activity leads to transient microtubule stabilization that delays abscission. In turn, stable microtubules promote the activity of Aurora B. When cells exit naive pluripotency, a decrease in Wnt signaling leads to a decrease in the activity of Aurora B, less stable microtubules, and a faster abscission. Overall, our data demonstrate that Aurora B-dependent microtubule stability controls abscission dynamics.

cell biology↗

bioRxiv2022

Direct observation of motor protein stepping in living cells using MINFLUX

Dynamic measurements of molecular machines can provide invaluable insights into their mechanism, but have been challenging in living cells. Here, we developed live-cell tracking of single fluorophores with nanometer spatial and millisecond temporal resolution in 2D and 3D using the recently introduced super-resolution technique MINFLUX. This allowed us to resolve the precise stepping motion of the motor protein kinesin-1 as it walks on microtubules in living cells. In addition, nanoscopic tracking of motors on microtubule of fixed cells enabled us to resolve their spatial organization with protofilament resolution. Our approach will enable future in vivo studies of motor protein kinetics in complex environments and super-resolution mapping of dense microtubule arrays, and pave the way towards monitoring functional conformational changes of protein machines at high spatiotemporal resolution in living systems.

biophysics↗

bioRxiv2021

The mechanochemical origins of the microtubule sliding motility within the kinesin-5 domain organization

The conserved kinesin-5 bipolar tetrameric motors slide apart microtubules during mitotic spindle assembly and elongation. Kinesin-5 bipolar organization originates from its conserved tetrameric helical minifilament, which position the C-terminal tail domains of two subunits near the N-terminal motor domains of two anti-parallel subunits (Scholey et al, 2014). This unique tetrameric structure enables kinesin-5 to simultaneously engage two microtubules and transmit forces between them, and for multiple kinesin-5 motors to organize via tail to motor interactions during microtubule sliding (Bodrug et al, 2020). Here, we show how these two structural adaptations, the kinesin-5 tail-motor domain interactions and the length of the tetrameric minifilament, determine critical aspects of kinesin-5 motility and sliding mechanisms. An x-ray structure of the 34-nm kinesin-5 minifilament reveals how the dual dimeric N-terminal coiled-coils emerge from the tetrameric central bundle. Using this structure, we generated active bipolar mini-tetrameric motors from Drosophila and human orthologs, which are half the length of native kinesin-5. Using single-molecule motility assays, we show that kinesin-5 tail domains promote mini-tetramers static pauses that punctuate processive motility. During such pauses, kinesin-5 mini-tetramers form multi-motor clusters mediated via tail to motor domain cross-interactions. These clusters undergo slow and highly processive motility and accumulate at microtubule plus-ends. In contrast to native kinesin-5, mini-tetramers require tail domains to initiate microtubule crosslinking. Although mini-tetramers are highly strained in initially aligning microtubules, they slide microtubules more efficiently than native kinesin-5, due to their decreased minifilament flexibility. Our studies reveal that the conserved kinesin-5 motor-tail mediated clustering and the length of the tetrameric minifilament are key features for sliding motility and are critical in organizing microtubules during mitotic spindle assembly and elongation.

cell biology↗

bioRxiv2021

Centriole-independent centrosome assembly in interphase mammalian cells

AbstractThe major microtubule-organizing center (MTOC) in animal cells, the centrosome, comprises a pair of centrioles surrounded by pericentriolar material (PCM), which nucleates and anchors microtubules. Centrosome assembly depends on PCM binding to centrioles, PCM self-association and dynein{-}mediated PCM transport, but the self-assembly properties of PCM in interphase cells are poorly understood. Here, we used experiments and modeling to study centriole-independent features of interphase PCM assembly. We showed that when centrioles are lost due to PLK4 depletion or inhibition, dynein-based PCM transport and PCM self-clustering are sufficient to form a single compact MTOC, which generates a dense radial microtubule array. Interphase PCM self-assembly depends on {gamma}-tubulin, pericentrin, CDK5RAP2 and ninein, but not NEDD1, CEP152 or CEP192. Formation of a compact acentriolar MTOC is inhibited by AKAP450-dependent PCM recruitment to the Golgi or by randomly organized CAMSAP2-stabilized microtubules, which keep PCM mobile and prevent its coalescence. Linking of CAMSAP2 to a minus-end-directed motor leads to the formation of an MTOC, but MTOC compaction requires cooperation with pericentrin-containing self-clustering PCM. Our data reveal that interphase PCM contains a set of components that can self-assemble into a compact structure and organize microtubules, but PCM self-organization is sensitive to motor-and microtubule-based rearrangement.

cell biology↗

bioRxiv2021

Optical nanoscopy reveals SARS-CoV-2-induced remodeling of human airway cells

A better understanding of host cell remodeling by the coronavirus SARS-CoV-2 is urgently needed to understand viral pathogenesis and guide drug development. Expression profiling and electron microscopy have frequently been used to study virus-host interactions, but these techniques do not readily enable spatial, sub-cellular and molecular analysis of specific cellular compartments. Here, we use diffraction-unlimited fluorescence microscopy to analyze how SARS-CoV-2 infection exploits and repurposes the subcellular architecture of primary human airway cells. Using STED nanoscopy, we detect viral entry factors along the motile cilia of ciliated cells and visualize key aspects of the viral life cycle. Using Tenfold Robust Expansion (TREx) microscopy, we analyze the extensively remodeled three-dimensional ultrastructure of SARS-CoV-2-infected ciliated cells and uncover Golgi fragmentation, emergence of large and atypical multivesicular bodies enclosing viral proteins, ciliary clustering, and remodeling of the apical surface. These results demonstrate a broadly applicable strategy to study how viruses reorganize host cells with spatial and molecular specificity and provide new insights into SARS-CoV-2 infection in primary human cell models.

cell biology↗