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Klena, N.

Publications and source records attributed to Klena, N..

7 recordsLinked to original sources

MicroSplit: Semantic Unmixing of Fluorescent Microscopy Data

Fluorescence microscopy, a key driver for progress in the life sciences, faces limitations due to the microscopes optics, fluorophore chemistry, and photon exposure limits, necessitating trade-offs in imaging speed, resolution, and depth. Here, we introduce Micro[S]plit, a computational multiplexing technique based on deep learning that allows multiple cellular structures to be imaged in a single fluorescent channel and then unmix them by computational means, allowing faster imaging and reduced photon exposure. We show that Micro[S]plit efficiently separates up to four superimposed noisy structures into distinct denoised fluorescent image channels. Furthermore, using Variational Splitting Encoder-Decoder (VSE) networks, our approach can sample diverse predictions from a trained posterior of solutions. The diversity of these samples scales with the uncertainty in a given input, allowing us to estimate the true prediction errors by computing the variability between posterior samples. We demonstrate the robustness of Micro[S]plit networks, which are trained for each splitting task at hand, across various datasets and noise levels and show its utility to image more, to image faster, and to improve downstream analysis. We provide Micro[S]plit along with all associated training and evaluation datasets as open resources, enabling life scientists to immediately benefit from the potential of computational multiplexing and thus help accelerate the rate of their scientific discovery process.

bioinformatics↗

Structure, interaction, and nervous connectivity of beta cell primary cilia

Primary cilia are sensory organelles present in many cell types. Based on an array of microtubules termed axoneme they form a specialized membrane compartment partaking in various signaling processes. Primary cilia of pancreatic islet beta cells play a role in autocrine and paracrine signaling and are linked to diabetes. Yet, the structural basis for their functions is unclear. We present three-dimensional reconstructions of complete mouse and human beta cell cilia, revealing a disorganized 9+0 axoneme structure. Within the islet, cilia are spatially confined within deep ciliary pockets or squeezed into narrow extracellular spaces between adjacent cells. Beta and alpha cell cilia physically interact with neighboring islet cells pushing and strongly bending their plasma membranes. Furthermore, beta cells can contain multiple cilia that can meet with other islet cell cilia in the extracellular space. Additionally, beta cell cilia establish connections with islet-projecting nerves. These findings highlight the pivotal role of beta cell primary cilia in islet cell connectivity, pointing at their potential functional role in integrating islet intrinsic and extrinsic signals. These novel insights contribute to understanding their significance in health and diabetes.

cell biology↗

The Tubulin Nano-Code: a protofilament-specific pattern of tubulin post-translational modifications regulates ciliary beating mechanics

Control of ciliary beating is crucial for motility and signaling in eukaryotic cells and requires spatially restricted interactions between axonemal proteins and specific protofilaments within the ciliary microtubules. How these interactions are regulated remains poorly understood, but increasing evidence indicates that tubulin post-translational modifications (tPTMs) are required for proper ciliary motility. The Tubulin Code refers to the concept that tPTMs can modulate the function of individual microtubules in cells. Here we use a combination of immuno-cryo-electron tomography, expansion microscopy and mutant analysis to show that, in motile cilia, tubulin glycylation and polyglutamylation form mutually exclusive protofilament-specific nano-patterns at sub-microtubular scale. We show that these two nano-patterns are consistent with the distributions of axonemal dyneins and nexin-dynein regulatory complexes, respectively, and are required for their regulation during ciliary beating. Our discovery of a tubulin nano-code in cilia highlights the need of higher-resolution studies also in other cellular compartments to understand the molecular role of tPTMs. One-Sentence SummaryTubulin post-translational modifications form nanopatterns at sub-microtubular scale that enable individual protofilaments to perform specific functions Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=126 SRC="FIGDIR/small/546853v1_ufig1.gif" ALT="Figure 1"> View larger version (62K): org.highwire.dtl.DTLVardef@253704org.highwire.dtl.DTLVardef@13f0a8forg.highwire.dtl.DTLVardef@1ce673dorg.highwire.dtl.DTLVardef@1dc04e1_HPS_FORMAT_FIGEXP M_FIG C_FIG

cell biology↗

Lack of CCDC146, a ubiquitous centriole and microtubule-associated protein, leads to non-syndromic male infertility in human and mouse

Genetic mutations are a recurrent cause of male infertility. Multiple morphological abnormalities of the flagellum (MMAF) syndrome is a heterogeneous genetic disease, with which more than 50 genes have been linked. Nevertheless, for 50% of patients with this condition, no genetic cause is identified. From a study of a cohort of 167 MMAF patients, pathogenic bi-allelic mutations were identified in the CCDC146 gene in two patients. This gene encodes a poorly characterized centrosomal protein which we studied in detail here. First, protein localization was studied in two cell lines. We confirmed the centrosomal localization in somatic cells and showed that the protein also presents multiple microtubule-related localizations during mitotic division, suggesting that it is a microtubule-associated protein (MAP). To better understand the function of the protein at the sperm level, and the molecular pathogenesis of infertility associated with CCDC146 mutations, two genetically modified mouse models were created: a Ccdc146 knock-out (KO) and a knock-in (KI) expressing a HA-tagged CCDC146 protein. KO male mice were completely infertile, and sperm exhibited a phenotype identical to our two MMAF patients phenotype with CCDC146 mutations. No other pathology was observed, and the animals were viable. CCDC146 expression starts during late spermiogenesis, at the time of flagellum biogenesis. In the spermatozoon, the protein is conserved but is not localized to centrioles, unlike in somatic cells, rather it is present in the axoneme at the level of microtubule doublets. Expansion microscopy associated with the use of the detergent sarkosyl to solubilize microtubule doublets, suggest that the protein may be a microtubule inner protein (MIP). At the subcellular level, the absence of CCDC146 affected the formation, localization and morphology of all microtubule-based organelles such as the manchette, the head-tail coupling apparatus (HTCA), and the axoneme. Through this study, we have characterized a new genetic cause of infertility, identified a new factor in the formation and/or structure of the sperm axoneme, and demonstrated that the CCDC146 protein plays several cellular roles, depending on the cell type and the stages in the cell cycle.

genetics↗

In situ architecture of the ciliary base reveals the stepwise assembly of IFT trains

The cilium is an antenna-like organelle that performs numerous cellular functions, including motility, sensing, and signaling. The base of the cilium contains a selective barrier that regulates the entry of large intraflagellar transport (IFT) trains, which carry cargo proteins required for ciliary assembly and maintenance. However, the native architecture of the ciliary base and the process of IFT train assembly remain unresolved. Here, we use in situ cryo-electron tomography to reveal native structures of the transition zone region and assembling IFT trains at the ciliary base. We combine this direct cellular visualization with ultrastructure expansion microscopy to describe the front-to-back stepwise assembly of IFT trains: IFT-B forms the backbone, onto which IFT-A, then dynein-1b, and finally kinesin-2 sequentially bind before entry into the cilium. One Sentence SummaryNative molecular structure of the ciliary transition zone and hierarchical order of IFT assembly visualized within Chlamydomonas cells.

cell biology↗

Kinesin-1 motility traced by an activity-based precipitating dye

Kinesin-1 is a processive motor protein that uses ATP-derived energy to transport a variety of intracellular cargoes toward the cell periphery. As tracks for cargo delivery, kinesin-1 uses a subset of microtubules within the dense microtubule network. It is still debated what defines the specific binding of kinesin-1 to a subset of microtubules. Therefore, the ability to visualize and monitor kinesin transport in live cells is critical to study the myriad of functions associated with cargo trafficking. Herein we report the discovery of a fluorogenic small molecule substrate for kinesin-1 that yields a precipitating dye. The activity of kinesin-1 thus leaves a fluorescent trail along its walking path and can be visualized without loss of signal due to diffusion. Kinesin-1 specific transport of cargo from the Golgi appears as trails of fluorescence over time.

biochemistry↗

The architecture of the centriole cartwheel-containing region revealed by cryo-electron tomography

Centrioles are evolutionarily conserved barrels of microtubule triplets that form the core of the centrosome and the base of the cilium. In the proximal region of the centriole, nine microtubule triplets attach to each other via A-C linkers and encircle a central cartwheel structure, which directs the early events of centriole assembly. While the crucial role of the proximal region in centriole biogenesis has been well documented in many species, its native architecture and evolutionary conservation remain relatively unexplored. Here, using cryo-electron tomography of centrioles from four evolutionarily distant species, including humans, we report on the architectural diversity of the centriolar proximal cartwheel-bearing region. Our work reveals that the cartwheel central hub, previously reported to have an 8.5 nm periodicity in Trichonympha, is constructed from a stack of paired rings with an average periodicity of [~]4 nm. In all four examined species, cartwheel inner densities are found inside the hubs ring-pairs. In both Paramecium and Chlamydomonas, the repeating structural unit of the cartwheel has a periodicity of 25 nm and consists of three ring-pairs with 6 radial spokes emanating and merging into a single bundle that connects to the triplet microtubule via the pinhead. Finally, we identified that the cartwheel is indirectly connected to the A-C linker through a flexible triplet-base structure extending from the pinhead. Together, our work provides unprecedented evolutionary insights into the architecture of the centriole proximal region, which underlies centriole biogenesis.

cell biology↗