Apicomplexan parasites such as Plasmodium spp. and Toxoplasma gondii possess unique tubulin-based structures, including subpellicular microtubules and apical polar rings, which are essential for parasite motility, host cell invasion, and replication. Apicortin, a microtubule-associated protein, contains a doublecortin (DC) domain and a partial tubulin polymerization-promoting protein (TPPP) domain, both implicated in microtubule binding and stabilization. How tubulin-based structures are maintained is poorly understood, but it may involve Apicortin, so far found only in apicomplexans and the placozoan Trichoplax adhaerens Here, we investigated the location and function of Apicortin in Plasmodium berghei Live-cell imaging of a transgenic parasite line expressing GFP-tagged Apicortin showed its location at the apical end of invasive parasite stages within the mosquito vector. Super-resolution and expansion microscopy revealed that Apicortin forms a distinct ringlike structure in the apical complex region at the apical end. However, deletion of the Apicortin gene had no effect on parasite development, indicating that this protein is not essential. This suggests that there may be redundancy or compensatory functions in the mechanisms that stabilize the apical complex.

This study reveals how Plasmodium kinases regulate MTOC, axoneme and kinetochore organisation in male gametogenesis, providing key insights into potential targets for malaria transmission control.

The chemokine CXCR4 receptor and epidermal growth factor receptor (EGFR) are cell surface receptors that are overexpressed in numerous types of cancer. In this study, we have investigated the formation of CXCR4-EGFR heteromers using bioluminescence resonance energy transfer (BRET) and nanobody-based proximity ligation assays (PLAs). The present study demonstrated that EGFR and CXCR4 can form oligomeric complexes that were capable of coupling to PLCγ, Gi proteins and β-arrestin-2. The presence of these oligomeric complexes was detected by PLA in native HeLa cells at endogenous levels of expression using receptor-selective nanobody-oligonucleotide conjugates. Furthermore, the individual receptor components of the oligomer underwent conformation changes in response to EGF and CXCL12, which in the case of Gi-signalling led to altered responses to combinations of CXCL12 and EGF. This may have clinical implications in those cancers where both EGFR and CXCR4 are overexpressed.

Three-dimensional imaging of live Caenorhabditis elegans commonly relies on sequential z-stack acquisition, which can be slow and susceptible to movement and photobleaching. Here, we used light-field microscopy to capture dye and delivery-dependent fluorescence patterns across intact adult worms in a single exposure per channel. With a 40×/1.20 NA water-immersion objective, each reconstructed dataset contained 121 axial slices spanning 109 µm at 0.91 µm spacing. In a representative adult, nematode signal extended from 40.88 to 85.4 µm, corresponding to approximately 44.5 µm of captured axial depth without sequential z scanning. Three fluorescence channels were acquired with a summed exposure time of 112 ms across a 685 × 1010 µm field of view. FM1-43 labelled intestinal, cuticular and vesicular structures, FM4-64 highlighted ingested bacteria and intestinal compartments, and Nile Red revealed vesicular and broader whole-organism fluorescence. Intrinsic blue and green autofluorescence signals were also resolved. These observations demonstrate rapid single-shot acquisition of whole-organism three-dimensional fluorescence information and show how delivery route influences the spatial distribution of commonly used fluorescent probes in C. elegans .

Apicomplexan parasites such as Plasmodium spp. and Toxoplasma gondii possess unique tubulin-based structures, including subpellicular microtubules and apical polar rings, which are essential for parasite motility, host cell invasion, and replication. How the stability of these structures is maintained is poorly understood, but it may involve Apicortin, a microtubule-associated protein, so-far found only in apicomplexans and the placozoan Trichoplax adhaerens . Apicortin contains a doublecortin (DC) domain and a partial tubulin polymerisation-promoting protein (TPPP) domain, both implicated in microtubule binding and stabilization. In this study, we investigated the location and function of Apicortin in Plasmodium berghei. Live cell imaging of a transgenic parasite line expressing GFP-tagged Apicortin showed that it was present at the apical end of invasive parasites only during development of transmission stages within the mosquito vector. High-resolution imaging using super-resolution and expansion microscopy, revealed that Apicortin forms a distinct ring-like structure in the apical complex region at the apical end of ookinetes and sporozoites. However, deletion of the Apicortin gene had no effect on parasite development and transmission through the mosquito, indicating that this protein is not essential. This suggests that there may be redundancy or compensatory functions in the mechanisms that stabilise the apical complex. ### Competing Interest Statement The authors have declared no competing interest. ERC advanced grant funded by UKRI Frontier Science to RT, EP/XO247761 Medical Research Council to RT Biotechnology and Biological Sciences Research Council to RT Biotechnology and Biological Sciences Research Council to CAM, BB/N018176/1 Cancer Research UK to AAH, FC001097 Wellcome Trust to AAH, FC001097

Mitosis in eukaryotes involves reorganisation of the nuclear envelope (NE) and microtubule-organising centres (MTOCs). During male gametogenesis in Plasmodium, the causative agent of malaria, mitosis is exceptionally rapid and highly divergent. Within 8 min, the haploid male gametocyte genome undergoes three replication cycles (1N to 8N), while maintaining an intact NE. Axonemes assemble in the cytoplasm and connect to a bipartite MTOC-containing nuclear pole (NP) and cytoplasmic basal body, producing eight flagellated gametes. The mechanisms coordinating NE remodelling, MTOC dynamics, and flagellum assembly remain poorly understood. We identify the SUN1-ALLAN complex as a novel mediator of NE remodelling and bipartite MTOC coordination during Plasmodium berghei male gametogenesis. SUN1, a conserved NE protein, localises to dynamic loops and focal points at the nucleoplasmic face of the spindle poles. ALLAN, a divergent allantoicase, has a location like that of SUN1, and these proteins form a unique complex, detected by live-cell imaging, ultrastructural expansion microscopy, and interactomics. Deletion of either SUN1 or ALLAN genes disrupts nuclear MTOC organisation, leading to basal body mis-segregation, defective spindle assembly, and impaired spindle microtubule-kinetochore attachment, but axoneme formation remains intact. Ultrastructural analysis revealed nuclear and cytoplasmic MTOC miscoordination, producing aberrant flagellated gametes lacking nuclear material. These defects block development in the mosquito and parasite transmission, highlighting the essential functions of this complex.

Sexual development and male gamete formation of the malaria parasite in the mosquito midgut are initiated by rapid endomitosis in the activated male gametocyte. This process is highly regulated by protein phosphorylation, specifically by three divergent male-specific protein kinases (PKs): CDPK4, SRPK1, and MAP2. Here, we localise each PK during male gamete formation using live-cell imaging, identify their putative interacting partners by immunoprecipitation, and determine the morphological consequences of their absence using ultrastructure expansion and transmission electron microscopy. Each PK has a distinct location in either the nuclear or the cytoplasmic compartment. Protein interaction studies revealed that CDPK4 and MAP2 interact with key drivers of rapid DNA replication, whereas SRPK1 is involved in RNA translation. The absence of each PK results in severe defects in either microtubule-organising centre organisation, kinetochore segregation, or axoneme formation. This study reveals the crucial role of these PKs during endomitosis in formation of the flagellated male gamete and uncovers some of their interacting partners that may drive this process.

Abstract For more than four thousand years technological advances have enabled us to see the invisible through the invention and development of microscopes that have delivered magnification alongside resolution. Over the same timescale this has led to the discovery of microscopic organisms and the birth of the science of microbiology. From ancient theories that an invisible life form existed light microscopy established their presence in the 1600s. Over the next couple of centuries light microscopes were developed with improved illumination and precision as microbiologists created ways to grow and sample their microbes. In so doing microscopy and microbiology extended our understanding of infection transmission from generalised miasma and germ theories to linking specific diseases with particular microbes to make diagnosis and prevention more reliable. Electron and fluorescent microscopy provided step changes in the visualisation of the finer detail of microbes, enabling the characterisation of internal structures and the unravelling of the molecular mechanisms of biological processes. We are now within an era of imaging microbes in three dimensions over time with sensitivity and super resolution to study the microbes in their natural habitat such as within infected tissues. With the advent of multi-modal, correlative and molecular imaging the future holds the promise of a full interrogation of the internal machineries of microbes and real-time tracking of their lifecycle and interactions. This will help deliver the next generation of antibiotics and alternative prevention strategies to enable everyone to live longer, healthier lives.

Mitosis in eukaryotes involves reorganization of the nuclear envelope (NE) and microtubule-organizing centers (MTOCs). In Plasmodium, the causative agent of malaria, male gametogenesis features an exceptionally rapid and divergent mitotic process. Within 8 minutes, haploid male gametocytes undergo three genome replication cycles (1N to 8N), assemble axonemes in the cytoplasm which connect to a bipartite microtubule-organizing centre (MTOC-containing nuclear pole and cytoplasmic basal body) and produce eight flagellated gametes while maintaining an intact NE. The mechanisms coordinating NE remodelling, MTOC dynamics, and flagella assembly remain poorly understood. Here, we identify the Sun1-Allan complex as a novel mediator of NE remodeling and bipartite MTOC coordination during Plasmodium male gametogenesis. Sun1, a conserved NE protein, localizes to dynamic loops and focal points near nuclear spindle poles. Allan, a divergent Allantoicase-domain protein, shows similar location with Sun1 at nuclear MTOCs. Despite the lack of canonical KASH-domain proteins in Plasmodium, Sun1 and Allan form a unique LINC-like complex, as shown by live-cell imaging, ultrastructural expansion microscopy, and interactomics. Deletion of Sun1 or Allan disrupts nuclear MTOC organization, leading to basal body mis-segregation, defective spindle assembly, and impaired kinetochore attachment, while axoneme formation remains intact. Ultrastructural analysis revealed nuclear and cytoplasmic MTOC miscoordination, producing aberrant flagellated gametes lacking nuclear material. Sun1 deletion also alters parasite lipid composition, underscoring its role in NE homeostasis. These defects block parasite transmission, highlighting the essential functions of this complex. This study uncovers a highly divergent mechanism of NE remodelling and bipartite MTOC organization in Plasmodium. The Sun1-Allan complex represents a non-canonical adaptation of the LINC complex, providing new insights into the evolution of closed mitosis and highlighting potential targets for blocking malaria transmission. ### Competing Interest Statement The authors have declared no competing interest.

Mitosis is an important process in the cell cycle required for cells to divide. Never in mitosis (NIMA)-like kinases (NEKs) are regulators of mitotic functions in diverse organisms. Plasmodium spp., the causative agent of malaria is a divergent unicellular haploid eukaryote with some unusual features in terms of its mitotic and nuclear division cycle that presumably facilitate proliferation in varied environments. For example, during the sexual stage of male gametogenesis that occurs within the mosquito host, an atypical rapid closed endomitosis is observed. Three rounds of genome replication from 1N to 8N and successive cycles of multiple spindle formation and chromosome segregation occur within 8 min followed by karyokinesis to generate haploid gametes. Our previous Plasmodium berghei kinome screen identified 4 Nek genes, of which 2, NEK2 and NEK4, are required for meiosis. NEK1 is likely to be essential for mitosis in asexual blood stage schizogony in the vertebrate host, but its function during male gametogenesis is unknown. Here, we study NEK1 location and function, using live cell imaging, ultrastructure expansion microscopy (U-ExM), and electron microscopy, together with conditional gene knockdown and proteomic approaches. We report spatiotemporal NEK1 location in real-time, coordinated with microtubule organising centre (MTOC) dynamics during the unusual mitoses at various stages of the Plasmodium spp. life cycle. Knockdown studies reveal NEK1 to be an essential component of the MTOC in male cell differentiation, associated with rapid mitosis, spindle formation, and kinetochore attachment. These data suggest that P. berghei NEK1 kinase is an important component of MTOC organisation and essential regulator of chromosome segregation during male gamete formation.

N6 adenosine and C5 cytosine modification of mRNAs, tRNAs and rRNAs are regulated by the behaviour of distinct sets of writer, reader and eraser effector proteins which are conventionally considered to function independently. Here, we provide evidence of global cross-regulatory and functional interaction between the m6A and m5C RNA methylation systems. We first show that m6A and m5C effector protein transcripts are subject to reciprocal base modification supporting the existence of co-regulatory post-transcriptional feedback loops. Using global mass spectrometry proteomic data generated after biological perturbation to identify proteins which change in abundance with effector proteins, we found novel co-regulatory cellular response relationships between m6A and m5C proteins such as between the m6A eraser, ALKBH5, and the m5C writer, NSUN4. Gene ontology analysis of co-regulated proteins indicated that m6A and m5C RNA cross-system control varies across cellular processes, e.g. proteasome and mitochondrial mechanisms, and post-translational modification processes such as SUMOylation and phosphorylation. We also uncovered novel relationships between effector protein networks including contributing to intellectual disability pathways. Finally, we provided in vitro confirmation of colocalisation between m6A-RNAs and the m5C reader protein, ALYREF, after synaptic NMDA activation. These findings have important implications for understanding control of RNA metabolism, cellular proteomic responses, and brain disease mechanisms.

Myotonic dystrophy type 1 (DM1) is a progressive, multisystemic disorder caused by an expansion of CTG repeats in the 3’ untranslated region of the DMPK gene. When transcribed the mutant RNAs accumulate in affected tissues appearing as distinct foci when visualised by in situ hybridisation. The RNA foci are aggregates of CUG repeat-containing RNAs that sequester RNA-binding proteins, particularly muscleblind-like (MBNL) proteins, leading to their dysfunction and causing downstream molecular and cellular defects. Here we show the double knock-out of MBNL1 and 2 prevents RNA foci formation and nuclear retention of mutant DMPK mRNA in DM1 cells as well as promoting their degradation and nuclear export. Using stochastic optical reconstruction microscopy (STORM), we find the presence of both large foci and micro foci in DM1 cells. Large foci consist of multiple DMPK transcripts, while many micro foci are (CUG)n fragments. The absence of MBNL proteins not only prevents the aggregation of multiple DMPK transcripts into large foci, but also promotes their degradation and nuclear processing. However, although a substantial amount of MBNL1 proteins are bound to the mutant transcripts, the pools of free MBNL1 proteins are similar in DM1 nuclei to those in controls. Furthermore, we have identified several factors that are involved in the control of mutant DMPK mRNA turnover, including XRN2, EXOSC10, UPF1 and STAU1. Our study indicates that these factors are implicated in the RNA foci accumulation and the degradation of mutant DMPK mRNA. UPF1 and STAU1 may have additional roles beyond degradation, impacting the nuclear processing of mutant DMPK mRNA. Our study also highlights the critical role of MBNL proteins in regulating mutant DMPK mRNA metabolism: the absence of MBNLs in DM1 appears to expedite the processing of mutant DMPK mRNA mediated by these RNA decay factors. Significance statement Our investigations uncovered valuable data on the RNA foci dynamics in DM1, revealing the intricate mechanisms that underlie their formation, stability, and turnover. Our findings also contributed to delineate the complex pathways involved in the transportation and degradation of the mutant mRNA and provided insights into the critical role played by MBNL proteins in these processes. Studying the degradation mechanism of mutant DMPK mRNA in myotonic dystrophy may provide a foundation for comprehending the mechanisms of RNA degradation in other diseases caused by short tandem repeat (STR) mutations, such as Huntington’s disease, Fragile X syndrome, and several types of ataxia. Additionally, the use of cutting-edge STORM technology can provide a valuable tool for investigating RNA foci in other STR expansion disorders.

Mechanisms of cell division are remarkably diverse, suggesting the underlying molecular networks among eukaryotes differ extensively. The Aurora family of kinases orchestrates the process of chromosome segregation and cytokinesis during cell division through precise spatiotemporal regulation of their catalytic activities by distinct scaffolds. Plasmodium spp., the causative agents of malaria, are unicellular eukaryotes that have three divergent aurora-related kinases (ARKs) and lack most canonical scaffolds/activators. The parasite uses unconventional modes of chromosome segregation during endomitosis and meiosis in sexual transmission stages within mosquito host. This includes a rapid threefold genome replication from 1N to 8N with successive cycles of closed mitosis, spindle formation and chromosome segregation within eight minutes (termed male gametogony). Kinome studies had previously suggested likely essential functions for all three Plasmodium ARKs during asexual mitotic cycles; however, little is known about their location, function, or their scaffolding molecules during unconventional sexual proliferative stages. Using a combination of super-resolution microscopy, mass spectrometry, and live-cell fluorescence imaging, we set out to investigate the role of the atypical Aurora paralog ARK2 to proliferative sexual stages using rodent malaria model Plasmodium berghei . We find that ARK2 primarily localises to the spindle apparatus in the vicinity of kinetochores during both mitosis and meiosis. Interactomics and co-localisation studies reveal a unique ARK2 scaffold at the spindle including the microtubule plus end-binding protein EB1, lacking conserved Aurora scaffold proteins. Gene function studies indicate complementary functions of ARK2 and EB1 in driving endomitotic divisions and thereby parasite transmission. Our discovery of a novel Aurora kinase spindle scaffold underlines the emerging flexibility of molecular networks to rewire and drive unconventional mechanisms of chromosome segregation in the malaria parasite Plasmodium .

AIMS:N6 -methyladenosine modification of RNA (m6 A) regulates translational control, which may influence neuronal dysfunction underlying neurodegenerative diseases.METHODS:Using microscopy and a machine learning approach, we performed cellular profiling of m6 A-RNA abundance and YTHDF1/YTHDF3 m6 A reader expression within four regions of the human brain from non-affected individuals and individuals with Parkinson's disease, dementia with Lewy bodies or mild cognitive impairment (MCI).RESULTS:In non-diseased tissue, we found that m6 A-modified RNAs showed cell-type and sub-compartment-specific variation. YTHDF1 and YTHDF3 showed opposing expression patterns in the cerebellum and the frontal and cingulate cortices. Machine learning quantitative image analysis revealed that m6 A-modified transcripts were significantly altered in localisation and abundance in disease tissue with significant decreases in m6 A-RNAs in Parkinson's disease, and significant increases in m6 A-RNA abundance in dementia with Lewy bodies. MCI tissue showed variability across regions but similar to DLB; in brain areas with an overall significant increase in m6 A-RNAs, modified RNAs within dendritic processes were reduced. Using mass spectrometry proteomic datasets to corroborate our findings, we found significant changes in YTHDF3 and m6 A anti-reader protein abundance in Alzheimer's disease (AD) and asymptomatic AD/MCI tissue and correlation with cognitive resilience.CONCLUSIONS:These results provide evidence for disrupted m6 A regulation in Lewy body diseases and a plausible mechanism through which RNA processing could contribute to the formation of Lewy bodies and other dementia-associated pathological aggregates. The findings suggest that manipulation of epitranscriptomic processes influencing translational control may lead to new therapeutic approaches for neurodegenerative diseases.

To design effective immunomodulatory implants, innate immune cell interactions at the surface of biomaterials need to be controlled and understood. The architectural design freedom of two-photon polymerization is used to produce arrays of surface-mounted, geometrically diverse 3D polymer objects. This reveals the importance of the interplay between architecture and materials chemistry in determining human macrophage fate in vitro. The ChemoArchiChip identifies key structure-function relationships and design rules from machine learning models to build a mechanistic understanding of cell attachment and polarization. Object shape, vertex/cone angle, and size are key drivers of attachment. Particular shapes are found to heavily modulate pro-or anti-inflammatory cell polarization, while triangular pyramids drastically reduce or even eliminate attachment. Caveola-dependent endocytosis is a principal mechanism by which cells respond to objects with sharp points; i.e., low vertex/cone angles. The discovery of these putative design rules points to surfaces decorated with architectures to augment implant performance.

The centriole/basal body (CBB) is an evolutionarily conserved organelle acting as a microtubule organising centre (MTOC) to nucleate cilia, flagella, and the centrosome. SAS4/CPAP is a conserved component associated with BB biogenesis in many model flagellated cells. Plasmodium, a divergent unicellular eukaryote and causative agent of malaria, displays an atypical, closed mitosis with an MTOC (or centriolar plaque), reminiscent of an acentriolar MTOC, embedded in the nuclear membrane. Mitosis during male gamete formation is accompanied by flagella formation. There are two MTOCs in male gametocytes: the acentriolar nuclear envelope MTOC for the mitotic spindle and an outer centriolar MTOC (the basal body) that organises flagella assembly in the cytoplasm. We show the coordinated location, association and assembly of SAS4 with the BB component, kinesin-8B, but no association with the kinetochore protein, NDC80, indicating that SAS4 is part of the BB and outer centriolar MTOC in the cytoplasm. Deletion of the SAS4 gene produced no phenotype, indicating that it is not essential for either male gamete formation or parasite transmission.

The centriole/basal body (CBB) is an evolutionarily conserved organelle acting as a microtubule organising centre (MTOC) to nucleate cilia, flagella and the centrosome. SAS4/CPAP is a conserved component associated with BB biogenesis in many model flagellated cells. Plasmodium , a divergent unicellular eukaryote and causative agent of malaria, displays an atypical closed mitosis with an MTOC, reminiscent of the acentriolar MTOC, embedded in the nuclear membrane at most proliferative stages. Mitosis during male gamete formation is accompanied by flagellum formation: within 15 minutes, genome replication (from 1N to 8N) and three successive rounds of mitosis without nuclear division occur, with coordinated axoneme biogenesis in the cytoplasm resulting in eight flagellated gametes. There are two MTOCs in male gametocytes. An acentriolar MTOC located with the nuclear envelope and a centriolar MTOC (basal body) located within the cytoplasm that are required for flagellum assembly. To study the location and function of SAS4 during this rapid process, we examined the spatial profile of SAS4 in real time by live cell imaging and its function by gene deletion. We show its absence during asexual proliferation but its presence and coordinated association and assembly of SAS4 with another basal body component, kinesin8B, which is involved in axoneme biogenesis. In contrast its separation from the nuclear kinetochore marker NDC80 suggests that SAS4 is part of the basal body and outer centriolar MTOC residing in the cytoplasm. However, deletion of the SAS4 gene produced no phenotype, indicating that it is not essential for male gamete formation or parasite transmission through the mosquito.### Competing Interest StatementThe authors have declared no competing interest.