Cellular & Molecular Imaging

OME-NGFF converted study from idr0090. Drug resistance threatens the effective prevention and treatment of an ever-increasing range of human infections. This highlights an urgent need for new and improved drugs with novel mechanisms of action to avoid cross-resistance. Current cell-based drug screens are, however, restricted to binary live/dead readouts with no provision for mechanism of action prediction. Machine learning methods are increasingly being used to improve information extraction from imaging data. Such methods, however, work poorly with heterogeneous cellular phenotypes and generally require time-consuming human-led training. We have developed a semi-supervised machine learning approach, combining human- and machine-labelled training data from mixed human malaria parasite cultures. Designed for high-throughput and high-resolution screening, our semi-supervised approach is robust to natural parasite morphological heterogeneity and correctly orders parasite developmental stages. Our approach also reproducibly detects and clusters drug-induced morphological outliers by mechanism of action, demonstrating the potential power of machine learning for accelerating cell-based drug discovery.

All symptoms of malaria disease are associated with the asexual blood stages of development, involving cycles of red blood cell (RBC) invasion and egress by the Plasmodium spp. merozoite. Merozoite invasion is rapid and is actively powered by a parasite actomyosin motor. The current accepted model for actomyosin force generation envisages arrays of parasite myosins, pushing against short actin filaments connected to the external milieu that drive the merozoite forwards into the RBC. In Plasmodium falciparum, the most virulent human malaria species, Myosin A (PfMyoA) is critical for parasite replication. However, the precise function of PfMyoA in invasion, its regulation, the role of other myosins and overall energetics of invasion remain unclear. Here, we developed a conditional mutagenesis strategy combined with live video microscopy to probe PfMyoA function and that of the auxiliary motor PfMyoB in invasion. By imaging conditional mutants with increasing defects in force production, based on disruption to a key PfMyoA phospho-regulation site, the absence of the PfMyoA essential light chain, or complete motor absence, we define three distinct stages of incomplete RBC invasion. These three defects reveal three energetic barriers to successful entry: RBC deformation (pre-entry), mid-invasion initiation, and completion of internalisation, each requiring an active parasite motor. In defining distinct energetic barriers to invasion, these data illuminate the mechanical challenges faced in this remarkable process of protozoan parasitism, highlighting distinct myosin functions and identifying potential targets for preventing malaria pathogenesis.

Plasmodium oocysts within the mosquito midgut epithelium produce sporozoites, the stage which is infective for the vertebrate host. The formation process of these sporozoites is termed sporogony and is still poorly understood. During sporogony a 30 nm thick longitudinal fiber, the rootlet fiber, connects the centriolar plaque of the nucleus to the apical polar ring at the tip of the forming sporozoite. It is hypothesized to play a role in trafficking secretory organelles and nuclear uptake into the newly forming sporozoite bud. A similar fiber was previously observed in Toxoplasma gondii which is formed by two striated fiber assemblins (SFAs). Here we characterize the two SFA homologs in P. berghei (PbSFA1/PBANKA_1227000, PbSFA2/PBANKA_1012000) via fluorescent tagging, confirming a fiber-like localization at the tips of nascent sporozoites in oocysts. Knockout of either SFA gene lead to significant reduction in oocyst numbers and a complete failure to produce any sporozoites. Upon investigation by electron microscopy and electron tomography, initiation of sporozoite formation could be observed but the rootlet fiber was absent in sporozoite buds. Strikingly, nuclear uptake was strongly affected, as no nuclei could be observed in elongated sporozoite buds. Further, elongated sporozoite buds failed to bud off, ultimately creating a network of incompletely formed ‘sporozoites’. These findings emphasize the role of the rootlet fiber in nuclear uptake und organization of sporozoite formation, making them essential for the progression through the mosquito.

Preventing parasite transmission from humans to mosquitoes is recognised to be critical for achieving elimination and eradication of malaria. Consequently developing new antimalarial drugs with transmission-blocking properties is a priority. Large screening campaigns have identified many new transmission-blocking molecules, however little is known about how they target transmissible Plasmodium falciparum stage V gametocytes, or how they affect their underlying cell biology. To respond to this knowledge gap, we have developed a machine learning image analysis pipeline to characterise and compare the cellular phenotypes generated by transmission-blocking molecules during male gametogenesis. Using this approach, we studied 40 molecules, categorising their activity based upon timing of action and visual effects on the organisation of tubulin and DNA in the cell. Our data both proposes new modes of action and corroborates existing modes of action of identified transmission-blocking molecules. Furthermore, the characterised molecules provide a new armoury of tool compounds to probe gametocyte cell biology and the generated imaging dataset provides a new reference for researchers to correlate molecular target or gene deletion to specific cellular phenotype. Our analysis pipeline is not optimised for a specific organism and could be applied to any fluorescence microscopy dataset containing cells delineated by bounding boxes, and so is extendible to any disease model.

Background Microsporidia sp. MB, a microsporidian symbiont found naturally in Anopheles mosquitoes, has potential as a novel malaria control tool since it can inhibit Plasmodium development and transmission. The most feasible MB-based Plasmodium control strategy would involve dissemination through live mosquito releases, or release of spores infective to mosquito larvae. To implement either strategy, establishment of stable mosquito colonies carrying MB at a high frequency is likely to be essential. The progeny of field caught An. gambiae s.l from Burkina Faso were isolated for individual egg laying and tested for MB. The progeny of the MB positive females were pooled and this process was repeated for multiple generations. The relative density of MB in different life stages and tissues of the An. coluzzii host was examined using a novel duplex qPCR assay. We also examined the impact of MB on fecundity through individualization for egg laying and counting of eggs. Finally, we examined laid eggs for presence of MB spores. Results Three An. coluzzii colonies and one An. gambiae s.l hybrid colony were established with high prevalence and density of MB and were maintained for more than two years with minimal intervention. MB prevalence and density was highest in eggs and adult females and lowest in L4 larvae; in adults density was highest in the gonads. Additionally, MB density increased in ovary samples following blood feeding which was likely due to the activation of sporogony. The production of spores is the reason why MB-carrying females lay more white non-hatching eggs and show a small reduction in fecundity. Conclusions Establishment of several stable MB carrying An. gambiae s.l colonies and understanding the impact of spores on fecundity are significant steps forward in developing MB as a malaria control tool.

Manuscript abstract: Malaria transmission relies on sporozoite formation in the mosquito midgut and subsequent salivary gland invasion. Despite their importance, the cell biology of these processes remains poorly understood. We apply Mosquito Tissue Ultrastructure Expansion Microscopy (MoTissU-ExM), which physically expands infected mosquito tissues while preserving host and parasite ultrastructure. MoTissU-ExM reveals parasite structures and organelles, including features previously seen only by electron microscopy and novel structures not observed before. We use MoTissU-ExM to investigate sporozoite formation and salivary gland invasion, focusing on rhoptries - secretory organelles critical for host cell invasion. We establish a timeline for rhoptry biogenesis, show that two rhoptries are consumed during salivary gland invasion, and provide the first evidence that rhoptry pairs are specialized for different invasion events. We further characterize RON11 as the first protein involved in sporozoite rhoptry biogenesis; its disruption produces sporozoites that specifically fail to invade salivary gland epithelial cells, blocking parasite transmission. Dataset description: This dataset contains all microscopy data associated with the linked publication "Unlocking new understanding of Plasmodium sporozoite biology with expansion microscopy". All samples were prepared by ultrastructure-expansion microscopy (U-ExM). All samples were imaged on either a Zeiss LSM900 or LSM980 microscope, using either Airyscan-SR or Airyscan-MPLX modes. File names will include the magnification of the objective lens used as follows: 5x = EC Plan-Neofluar 5x/0.16NA Air 10x = Ziess Plan-Apochromat 10x/0.45NA air 20x = Ziess Plan-Apochromat 20x/0.8NA air 40x = Zeiss C-Apochromat 40x/1.2NA water-immersion autocorr M27 63x = Zeiss Plan-Apochromat 63x/1.4NA oil-immersion M27 Images are of mosquito tissues, or isolated parasites, from three Plasmodium species - berghei (Pb), falciparum (Pf), and yoelii (Py). Images are sorted and named as follows (folder name, file name) Plasmodium species > Tissue type/site of isolation > Parasite strain > Species abbreviation, MG/SG, Harvest day(dpi), Dye/Fluorophores (405nm -> 647nm), Objective, Image number (1->X), as (airyscan) For example, the third image taken of a P. berghei oocyst with the RON11iKD parasite line, that was harvested on Day 14 post infection, stained with NHS Ester AF405, BODIPY-FL, anti-Tubulin AF555, and Sytox Red, and imaged on the 40x-objective would be listed as follows: Plasmodium berghei > Infected midguts > RON11iKD > RON11KD MG 14dpi NHSBFlTub-SytR 40x 1 as The majority of images in this dataset are z-stacked images, but for many oocysts a single-slice image of the whole oocyst was taken. When this is the case, the single-slice image will be indicated with "SNAP". A list of the acronyms and abbreviations used in file names are as follows MG = Midgut SG = Salivary gland Spz = Sporozoite HC = Haemocoel dpi = Days post infection NHS = NHS Ester Alexa Fluor 405 BFl = Bodipy-FL-Ceramide BTRc = Bodipy-TR-Ceramide SytR = Sytox Deep Red Tub = anti-tubulin antibody CSP = anti-circumsporozoite protein antibody RAP1 = anti-rhoptry associated protein 1 antibody iKD = Inducible knockdown Ctrl = Control KD = Knockdown RON4 = anti-rhoptry neck protein 4 antibody GFP = anti-green fluorescent protein antibody WGA = Wheat germ aglutinnin BIP = anti-BiP antibody ERD2 = anti-ERD2 antibody

We used cryo 3D FIB/SEM to develop a new approach for characterizing fouling induced by biomolecule filtration through polymeric membranes. During observation, some dust particles were found frozen onto the side of the sample and on the sample holder. Those particles resemble tiny figures in motion, perhaps ice skating or engaged in a playful snowball fight. What might otherwise go unnoticed becomes a lively winter scene, where chance and imagination bring character to the microscopic world. Runner-up image of Euro-BioImaging's Contest: Four Seasons of the Invisible - Winter.

Purpose: Homeostatic plasticity is crucial for maintaining stable neural activity by adjusting strength and intrinsic properties of synapses. This mechanism is vital for normal nervous system function and plays a role in various neurological conditions, including retinal degenerations. Sensitive night vision has been shown in P23H/Gnat2-/- retinitis pigmentosa (RP) mice, which lack cone phototransduction and rely solely on rods, even after losing more than half of their rod photoreceptors. While homeostatic plasticity has been proposed as a potential explanation, the underlying molecular mechanisms remain unclear. The aim of this study was to investigate the molecular basis of this phenomenon. Methods: Single cell RNA-sequencing (scRNA-seq) and bulk retina proteomics were used to investigate the transcriptomic and proteomic changes of the degenerating retinas in 1-month-old P23H/Gnat2-/- RP and Gnat2-/- control mice. Immunohistochemistry was used to analyze the expression of synaptic SNARE complex and vesicle proteins, SNAP25 and SYT1, in the outer plexiform layer, the site of rod axon terminals. Results: This study shows a significant upregulation of genes encoding synaptic SNARE complex and vesicle proteins (Snap25, Stxbp1, and Syt1) in P23H mouse rods. Bulk retina proteomics analysis shows trends toward upregulation of the corresponding proteins as well as upregulation of many matrix-associated and trans-synaptic-complex proteins. Immunohistochemistry shows persistent SYT1 and SNAP25 expression in the outer plexiform layer of P23H/Gnat2-/- mice despite significant rod death. Conclusions: Rod degeneration induces molecular changes in the P23H/Gnat2-/- mouse rods that suggest synaptic plasticity and strengthening of rod-rod bipolar cell synaptic transmission in early RP.

Plasmodium parasites, the causative agents of malaria, undergo complex replication within vertebrate and insect hosts, presenting unique opportunities for therapeutic intervention. A key challenge during these replication events, i.e., schizogony in vertebrate red blood cells and sporogony in oocysts within mosquitos, is ensuring the faithful partitioning of nuclei and organelles into the numerous daughter cells that form at once from a single parent. While nuclear microtubule-organizing centers, or centriolar plaques (CPs), have been hypothesized to play a central role in this process, the molecular mediators linking the CPs and organelles remain incompletely defined. Here, we characterize two striated fiber assemblin (SFA) homologs, SFA1 and SFA2, in Plasmodium falciparum and Plasmodium berghei across two hosts. We show that these SFAs form a physical bridge between the CP and the nascent apical poles of daughter cells, facilitating high-fidelity progeny formation during schizogony and sporogony. Loss of SFA function disrupts merozoite and sporozoite formation, with profound consequences for transmission. These findings establish SFAs as essential organizers of parasite morphogenesis and highlight them as potential targets for antimalarial therapies. This submission includes the source microscopy image data for experiments performed in P. falciparum.

Polyphasic studies on cyanobacterial biodiversity are scarce in the Caribbean and have never been conducted in the Dominican Republic. In this study we analysed sixteen cyanobacterial isolates sampled from biofilms growing on rocks and related to freshwater, saline and thermal environments across the country. A polyphasic approach was employed, incorporating 16S rRNA gene phylogenetic analysis, molecular identity assessments (p-distance), 16S–23S ITS sequence comparison and secondary structure analysis, alongside morphological characterization and habitat comparison. The strains were distributed across the orders Nodosilineales, Oculatellales, Oscillatoriales and Nostocales. Eleven strains were identified as belonging to Almyronema, Euryhalinema, Salileptolyngbya, Nodosilinea, Reticulonema, Vacuolonema, Capilliphycus, Purpureonostoc, Violetonostoc, Desmonostoc and Hapalosiphon. Additionally, four strains formed three distinct clades and presented low 16S rRNA gene identities with their phylogenetically closest genera, suggesting the existence of three undescribed lineages pending comprehensive polyphasic study. At the species level, four strains were considered undescribed lineages pending comprehensive polyphasic study and one strain (LEGE 171504) was described as a new species of Salileptolyngbya. This study represents the first investigation into the cyanobacterial diversity of Dominican Republic expanding the distribution of the identified taxa. Moreover, this is the first report of Salileptolyngbya in the Caribbean region and in brackish waters, as well as the first newly described cyanobacterial species from the Dominican Republic.