Biogenesis, inheritance, and 3D ultrastructure of the microsporidian mitosome.

During the reductive evolution of obligate intracellular parasites called microsporidia, a tiny remnant mitochondrion (mitosome) lost its typical cristae, organellar genome, and most canonical functions. Here, we combine electron tomography, stereology, immunofluorescence microscopy, and bioinformatics to characterise mechanisms of growth, division, and inheritance of this minimal mitochondrion in two microsporidia species (grown within a mammalian RK13 culture-cell host). Mitosomes of Encephalitozoon cuniculi (2-12/cell) and Trachipleistophora hominis (14-18/nucleus) displayed incremental/non-phasic growth and division and were closely associated with an organelle identified as equivalent to the fungal microtubule-organising centre (microsporidian spindle pole body; mSPB). The mitosome-mSPB association was resistant to treatment with microtubule-depolymerising drugs nocodazole and albendazole. Dynamin inhibitors (dynasore and Mdivi-1) arrested mitosome division but not growth, whereas bioinformatics revealed putative dynamins Drp-1 and Vps-1, of which, Vps-1 rescued mitochondrial constriction in dynamin-deficient yeast (Schizosaccharomyces pombe). Thus, microsporidian mitosomes undergo incremental growth and dynamin-mediated division and are maintained through ordered inheritance, likely mediated via binding to the microsporidian centrosome (mSPB).

Differential roles for ACBD4 and ACBD5 in peroxisome-ER interactions and lipid metabolism.

Peroxisomes and the endoplasmic reticulum (ER) are intimately linked subcellular organelles, physically connected at membrane contact sites. While collaborating in lipid metabolism, for example, of very long-chain fatty acids (VLCFAs) and plasmalogens, the ER also plays a role in peroxisome biogenesis. Recent work identified tethering complexes on the ER and peroxisome membranes that connect the organelles. These include membrane contacts formed via interactions between the ER protein VAPB (vesicle-associated membrane protein-associated protein B) and the peroxisomal proteins ACBD4 and ACBD5 (acyl-coenzyme A-binding domain protein). Loss of ACBD5 has been shown to cause a significant reduction in peroxisome-ER contacts and accumulation of VLCFAs. However, the role of ACBD4 and the relative contribution these two proteins make to contact site formation and recruitment of VLCFAs to peroxisomes remain unclear. Here, we address these questions using a combination of molecular cell biology, biochemical, and lipidomics analyses following loss of ACBD4 or ACBD5 in HEK293 cells. We show that the tethering function of ACBD5 is not absolutely required for efficient peroxisomal ß-oxidation of VLCFAs. We demonstrate that loss of ACBD4 does not reduce peroxisome-ER connections or result in the accumulation of VLCFAs. Instead, the loss of ACBD4 resulted in an increase in the rate of ß-oxidation of VLCFAs. Finally, we observe an interaction between ACBD5 and ACBD4, independent of VAPB binding. Overall, our findings suggest that ACBD5 may act as a primary tether and VLCFA recruitment factor, whereas ACBD4 may have regulatory functions in peroxisomal lipid metabolism at the peroxisome-ER interface.

Scoping intergenerational effects of nanoplastic on the lipid reserves of Antarctic krill embryos.

Antarctic krill (Euphausia superba) plays a central role in the Antarctic marine food web and biogeochemical cycles and has been identified as a species that is potentially vulnerable to plastic pollution. While plastic pollution has been acknowledged as a potential threat to Southern Ocean marine ecosystems, the effect of nanoplastics (<1000 nm) is poorly understood. Deleterious impacts of nanoplastic are predicted to be higher than that of larger plastics, due to their small size which enables their permeation of cell membranes and potentially provokes toxicity. Here, we investigated the intergenerational impact of exposing Antarctic krill to nanoplastics. We focused on whether embryonic energy resources were affected when gravid female krill were exposed to nanoplastic by determining lipid and fatty acid compositions of embryos produced in incubation. Embryos were collected from females who had spawned under three different exposure treatments (control, nanoplastic, nanoplastic + algae). Embryos collected from each maternal treatment were incubated for a further 6 days under three nanoplastic exposure treatments (control, low concentration nanoplastic, and high concentration nanoplastic). Nanoplastic additions to seawater did not impact lipid metabolism (total lipid or fatty acid composition) across the maternal or direct embryo treatments, and no interactive effects were observed. The provision of a food source during maternal exposure to nanoplastic had a positive effect on key fatty acids identified as important during embryogenesis, including higher total polyunsaturated fatty acids (PUFA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) when compared to the control and nanoplastic treatments. Whilst the short exposure time was ample for lipids from maternally digested algae to be incorporated into embryos, we discuss why the nanoplastic-fatty acid relationship may be more complex. Our study is the first to scope intergeneration effects of nanoplastic on Antarctic krill lipid and fatty acid reserves. From this, we suggest directions for future research including long term exposures, multi-stressor scenarios and exploring other critical energy reserves such as proteins.

Antagonistic Mobile Genetic Elements Can Counteract Each Other's Effects on Microbial Community Composition.

Bacteriophages ("phages") are hypothesized to be key drivers of bacterial population dynamics, driving microbial community composition, but empirical support for this is mixed. One reason why phages may have a less-than-expected impact on community composition is that many different phages and other mobile genetic elements (MGEs) interact with each bacterium. For instance, the same phage may have higher or lower costs to different bacterial strains or species. Assuming that resistance or susceptibility to MGE infection is not consistent across all MGEs, a simple prediction is that the net effect of MGEs on each bacterial taxon may converge with an increasing number of interactions with different MGEs. We formalized this prediction using in silico population dynamics simulations and then carried out experiments using three bacterial species, one generalist conjugative plasmid, and three species-specific phages. While the presence of only phages or only the plasmid altered community structure, these differential effects on community structure canceled out when both were together. The effects of MGEs were largely indirect and could not be explained by simple pairwise bipartite interactions (i.e., between each MGE and each bacterial species). Our results suggest that the effects of MGEs may be overestimated by studies that focus on a single MGE and not on interactions among multiple MGEs. IMPORTANCE While bacteriophages ("phages") are often cited as some of the key drivers of microbial diversity, evidence for this is greatly mixed. We demonstrate, in silico and experimentally, that the impact of phages, an example of a mobile genetic element (MGE), on community structure can diminish with increasing MGE diversity. This is because MGEs can have diverse effects on host fitness, and therefore as diversity increases, their individual effects cancel out, returning communities back to an MGE-free state. In addition, interactions in mixed-species and MGE communities could not be predicted from simple pairwise interactions, highlighting the difficulty in generalizing a MGE's effect from pairwise studies.

Ultrastructural Analysis and Quantification of Peroxisome-Organelle Contacts.

Transmission electron microscopy (TEM) has long been a vital technology to visualize the interaction of cellular compartments at the highest possible resolution. While this paved the way to describing organelles within the cellular context in detail, TEM has long been underused to generate quantitative data, analyzing those interactions as well as underlying mechanisms leading to their formation and modification. Here we describe a simple stereological method to unbiasedly assess the extent of organelle-organelle membrane contact sites, able to efficiently generate accurate and reproducible quantitative data from cultured mammalian cells prepared for TEM.

Short Depuration of Oysters Intended for Human Consumption Is Effective at Reducing Exposure to Nanoplastics.

Nanoplastics (NPs; <1 µm) have greater availability to marine organisms than microplastics (1-5000 µm). Understanding NP uptake and depuration in marine organisms intended for human consumption is imperative for food safety, but until now it has been limited due to analytical constraints. Oysters (Crassostrea gigas) were exposed to polystyrene NPs doped with palladium (Pd), allowing the measurements of their uptake into tissues by inductively coupled plasma mass spectrometry (ICP-MS) combined with electron microscopy. Oysters were exposed for 6 days (d) to "Smooth" or "Raspberry" NPs, followed by 30 d of depuration with the aim of assessing the NP concentration in C. gigas following exposure, inferring the accumulation and elimination rates, and understanding the clearance of Pd NPs during the depuration period. After 6 d, the most significant accumulation was found in the digestive gland (106.6 and 135.3 µg g-1 dw, for Smooth and Raspberry NPs, respectively) and showed the most evident depuration (elimination rate constant KSmooth = 2 d-1 and KRaspberry = 0.2 d-1). Almost complete depuration of the Raspberry NPs occurred after 30 d. While a post-harvesting depuration period of 24-48 h for oysters could potentially reduce the NP content by 75%, more research to validate these findings, including depuration studies of oysters from the field, is required to inform practices to reduce human exposure through consumption.

Nature of ß-1,3-Glucan-Exposing Features on Candida albicans Cell Wall and Their Modulation.

Candida albicans exists as a commensal of mucosal surfaces and the gastrointestinal tract without causing pathology. However, this fungus is also a common cause of mucosal and systemic infections when antifungal immune defenses become compromised. The activation of antifungal host defenses depends on the recognition of fungal pathogen-associated molecular patterns (PAMPs), such as ß-1,3-glucan. In C. albicans, most ß-1,3-glucan is present in the inner cell wall, concealed by the outer mannan layer, but some ß-1,3-glucan becomes exposed at the cell surface. In response to host signals, such as lactate, C. albicans induces the Xog1 exoglucanase, which shaves exposed ß-1,3-glucan from the cell surface, thereby reducing phagocytic recognition. We show here that ß-1,3-glucan is exposed at bud scars and punctate foci on the lateral wall of yeast cells, that this exposed ß-1,3-glucan is targeted during phagocytic attack, and that lactate-induced masking reduces ß-1,3-glucan exposure at bud scars and at punctate foci. ß-1,3-Glucan masking depends upon protein kinase A (PKA) signaling. We reveal that inactivating PKA, or its conserved downstream effectors, Sin3 and Mig1/Mig2, affects the amounts of the Xog1 and Eng1 glucanases in the C. albicans secretome and modulates ß-1,3-glucan exposure. Furthermore, perturbing PKA, Sin3, or Mig1/Mig2 attenuates the virulence of lactate-exposed C. albicans cells in Galleria. Taken together, the data are consistent with the idea that ß-1,3-glucan masking contributes to Candida pathogenicity. IMPORTANCE Microbes that coexist with humans have evolved ways of avoiding or evading our immunological defenses. These include the masking by these microbes of their "pathogen-associated molecular patterns" (PAMPs), which are recognized as "foreign" and used to activate protective immunity. The commensal fungus Candida albicans masks the proinflammatory PAMP ß-1,3-glucan, which is an essential component of its cell wall. Most of this ß-1,3-glucan is hidden beneath an outer layer of the cell wall on these microbes, but some can become exposed at the fungal cell surface. Using high-resolution confocal microscopy, we examine the nature of the exposed ß-1,3-glucan at C. albicans bud scars and at punctate foci on the lateral cell wall, and we show that these features are targeted by innate immune cells. We also reveal that downstream effectors of protein kinase A (Mig1/Mig2, Sin3) regulate the secretion of major glucanases, modulate the levels of ß-1,3-glucan exposure, and influence the virulence of C. albicans in an invertebrate model of systemic infection. Our data support the view that ß-1,3-glucan masking contributes to immune evasion and the virulence of a major fungal pathogen of humans.

PEX11ß and FIS1 cooperate in peroxisome division independently of mitochondrial fission factor.

Peroxisome membrane dynamics and division are essential to adapt the peroxisomal compartment to cellular needs. The peroxisomal membrane protein PEX11ß (also known as PEX11B) and the tail-anchored adaptor proteins FIS1 (mitochondrial fission protein 1) and MFF (mitochondrial fission factor), which recruit the fission GTPase DRP1 (dynamin-related protein 1, also known as DNML1) to both peroxisomes and mitochondria, are key factors of peroxisomal division. The current model suggests that MFF is essential for peroxisome division, whereas the role of FIS1 is unclear. Here, we reveal that PEX11ß can promote peroxisome division in the absence of MFF in a DRP1- and FIS1-dependent manner. We also demonstrate that MFF permits peroxisome division independently of PEX11ß and restores peroxisome morphology in PEX11ß-deficient patient cells. Moreover, targeting of PEX11ß to mitochondria induces mitochondrial division, indicating the potential for PEX11ß to modulate mitochondrial dynamics. Our findings suggest the existence of an alternative, MFF-independent pathway in peroxisome division and report a function for FIS1 in the division of peroxisomes. This article has an associated First Person interview with the first authors of the paper.

Differential routing and disposition of the long-chain saturated fatty acid palmitate in rodent vs human beta-cells.

BACKGROUND: Rodent and human ß-cells are differentially susceptible to the "lipotoxic" effects of long-chain saturated fatty acids (LC-SFA) but the factors accounting for this are unclear. Here, we have studied the intracellular disposition of the LC-SFA palmitate in human vs rodent ß-cells and present data that reveal new insights into the factors regulating ß-cell lipotoxicity. METHODS: The subcellular distribution of the LC-SFA palmitate was studied in rodent (INS-1E and INS-1 823/13 cells) and human (EndoC-ßH1) ß-cells using confocal fluorescence and electron microscopy (EM). Protein expression was assessed by Western blotting and cell viability, by vital dye staining. RESULTS: Exposure of INS-1 cells to palmitate for 24 h led to loss of viability, whereas EndoC-ßH1 cells remained viable even after 72 h of treatment with a high concentration (1 mM) of palmitate. Use of the fluorescent palmitate analogue BODIPY FL C16 revealed an early localisation of the LC-SFA to the Golgi apparatus in INS-1 cells and this correlated with distention of intracellular membranes, visualised under the EM. Despite this, the PERK-dependent ER stress pathway was not activated under these conditions. By contrast, BODIPY FL C16 did not accumulate in the Golgi apparatus in EndoC-ßH1 cells but, rather, co-localised with the lipid droplet-associated protein, PLIN2, suggesting preferential routing into lipid droplets. When INS-1 cells were treated with a combination of palmitate plus oleate, the toxic effects of palmitate were attenuated and BODIPY FL C16 localised primarily with PLIN2 but not with a Golgi marker. CONCLUSION: In rodent ß-cells, palmitate accumulates in the Golgi apparatus at early time points whereas, in EndoC- ßH1 cells, it is routed preferentially into lipid droplets. This may account for the differential sensitivity of rodent vs human ß-cells to "lipotoxicity" since manoeuvres leading to the incorporation of palmitate into lipid droplets is associated with the maintenance of cell viability in both cell types.

The Use of Off-Label Medications in Newborn Infants Despite an Approved Alternative Being Available-Results of a National Survey.

Neonates continue to be treated with off-label or unlicensed drugs while in hospital. However, some medications that have previously been used in adults underwent clinical testing and licensure for use with a different indication in the neonatal and pediatric population. Almost always, the marketing of these newly approved substances in a niche indication is accompanied by a steep increase in the price of the compound. We investigated the use of the approved formulation or the cheaper off-label alternative of Ibuprofen (Pedea®), Propanolol (Hemangiol®) and Caffeine Citrate (Peyona®) in neonatal clinical practice by conducting a National Survey of 214 Perinatal Centers in Germany. We also assessed price differences between on- and off-label alternatives and the extend of the clinical development program of the on-label medication in the neonatal population. On-label medication was more frequently used than the off-label alternative in all indications (PDA: on-label to off-label ratio 1:0.26, Apnea: 1:0.56, Hemangioma 1:0.76). All sponsors did conduct placebo-controlled Phase III trials with efficacy and safety endpoints in the target population and the number of participants in the target population varied between 82 and 497. Costs for the three drugs in their approved and marketed formulations increased in median 405-fold compared with the corresponding off-label alternative. Overall, about one out of three neonatologists prescribed an off-label or non-approved drug to patients despite an alternative medication that is approved for the indication in the target population being available.

Regulating peroxisome-ER contacts via the ACBD5-VAPB tether by FFAT motif phosphorylation and GSK3ß.

Peroxisomes and the endoplasmic reticulum (ER) cooperate in cellular lipid metabolism. They form membrane contacts through interaction of the peroxisomal membrane protein ACBD5 (acyl-coenzyme A-binding domain protein 5) and the ER-resident protein VAPB (vesicle-associated membrane protein-associated protein B). ACBD5 binds to the major sperm protein domain of VAPB via its FFAT-like (two phenylalanines [FF] in an acidic tract) motif. However, molecular mechanisms, which regulate formation of these membrane contact sites, are unknown. Here, we reveal that peroxisome-ER associations via the ACBD5-VAPB tether are regulated by phosphorylation. We show that ACBD5-VAPB binding is phosphatase-sensitive and identify phosphorylation sites in the flanking regions and core of the FFAT-like motif, which alter interaction with VAPB-and thus peroxisome-ER contact sites-differently. Moreover, we demonstrate that GSK3ß (glycogen synthase kinase-3 ß) regulates this interaction. Our findings reveal for the first time a molecular mechanism for the regulation of peroxisome-ER contacts in mammalian cells and expand the current model of FFAT motifs and VAP interaction.

A new method for isolating and analysing coccospheres within sediment.

Size is a fundamental cellular trait that is important in determining phytoplankton physiological and ecological processes. Fossil coccospheres, the external calcite structure produced by the excretion of interlocking plates by the phytoplankton coccolithophores, can provide a rare window into cell size in the past. Coccospheres are delicate however and are therefore poorly preserved in sediment. We demonstrate a novel technique combining imaging flow cytometry and cross-polarised light (ISX+PL) to rapidly and reliably visually isolate and quantify the morphological characteristics of coccospheres from marine sediment by exploiting their unique optical and morphological properties. Imaging flow cytometry combines the morphological information provided by microscopy with high sample numbers associated with flow cytometry. High throughput imaging overcomes the constraints of labour-intensive manual microscopy and allows statistically robust analysis of morphological features and coccosphere concentration despite low coccosphere concentrations in sediments. Applying this technique to the fine-fraction of sediments, hundreds of coccospheres can be visually isolated quickly with minimal sample preparation. This approach has the potential to enable rapid processing of down-core sediment records and/or high spatial coverage from surface sediments and may prove valuable in investigating the interplay between climate change and coccolithophore physiological/ecological response.

Identification and Characterization of Highly Fluorescent Pigment Cells in Embryos of the Arabian Killifish (Aphanius Dispar).

The Arabian killifish, Aphanius dispar, is a small tropical teleost fish living in wide range of habitats in sea water and fresh water in the Middle East. Here, we report extraordinary fluorescent pigment cells in the Arabian killifish embryo. These cells appear brown in transmitted light, yellowish white in reflected light, and as strong fluorescence in GFP and RFP filters. TEM and confocal microscopy analyses show the fluorescence emanates from leucosome-like pigment organelles. The cells express the gene encoding GTP cyclohydrolase (gch), a marker for leucophores and xanthophore. Gene knockdown and knockout of gch using morpholino or CRISPR-Cas9 induced loss of fluorescence in these embryos, indicating a crucial role of the enzyme and the associated pterine biosynthesis pathway in the generation of the fluorescence. We concluded that these cells are a highly fluorescent subtype of leucophores and have named them as fluoroleucophores.

Development of the electric organ in embryos and larvae of the knifefish, Brachyhypopomus gauderio.

South American Gymnotiform knifefish possess electric organs that generate electric fields for electro-location and electro-communication. Electric organs in fish can be derived from either myogenic cells (myogenic electric organ/mEO) or neurogenic cells (neurogenic electric organ/nEO). To date, the embryonic development of EOs has remained obscure. Here we characterize the development of the mEO in the Gymnotiform bluntnose knifefish, Brachyhypopomus gauderio. We find that EO primordial cells arise during embryonic stages in the ventral edge of the tail myotome, translocate into the ventral fin and develop into syncytial electrocytes at early larval stages. We also describe a pair of thick nerve cords that flank the dorsal aorta, the location and characteristic morphology of which are reminiscent of the nEO in Apteronotid species, suggesting a common evolutionary origin of these tissues. Taken together, our findings reveal the embryonic origins of the mEO and provide a basis for elucidating the mechanisms of evolutionary diversification of electric charge generation by myogenic and neurogenic EOs.

Mitochondrial fission factor (MFF) is a critical regulator of peroxisome maturation.

Peroxisomes are highly dynamic subcellular compartments with important functions in lipid and ROS metabolism. Impaired peroxisomal function can lead to severe metabolic disorders with developmental defects and neurological abnormalities. Recently, a new group of disorders has been identified, characterised by defects in the membrane dynamics and division of peroxisomes rather than by loss of metabolic functions. However, the contribution of impaired peroxisome plasticity to the pathophysiology of those disorders is not well understood. Mitochondrial fission factor (MFF) is a key component of both the peroxisomal and mitochondrial division machinery. Patients with MFF deficiency present with developmental and neurological abnormalities. Peroxisomes (and mitochondria) in patient fibroblasts are highly elongated as a result of impaired organelle division. The majority of studies into MFF-deficiency have focused on mitochondrial dysfunction, but the contribution of peroxisomal alterations to the pathophysiology is largely unknown. Here, we show that MFF deficiency does not cause alterations to overall peroxisomal biochemical function. However, loss of MFF results in reduced import-competency of the peroxisomal compartment and leads to the accumulation of pre-peroxisomal membrane structures. We show that peroxisomes in MFF-deficient cells display alterations in peroxisomal redox state and intra-peroxisomal pH. Removal of elongated peroxisomes through induction of autophagic processes is not impaired. A mathematical model describing key processes involved in peroxisome dynamics sheds further light into the physical processes disturbed in MFF-deficient cells. The consequences of our findings for the pathophysiology of MFF-deficiency and related disorders with impaired peroxisome plasticity are discussed.

Fluorescent tools to analyse peroxisome-ER interactions in mammalian cells.

Peroxisomes and the endoplasmic reticulum (ER) cooperate extensively in lipid-related metabolic pathways, and the ER also provides phospholipids to enable the peroxisomal membrane to expand prior to division. Recently, we identified peroxisomal proteins ACBD5 and ACBD4, and the ER protein VAPB as tethering components which physically interact to foster peroxisome-ER associations at membrane contact sites. Overexpression or loss of these tether proteins alters the extent of peroxisome-ER interactions, impacting on lipid exchange between these two compartments. To facilitate further studies into peroxisome-ER associations at the level of membrane contact sites, their role, composition and regulation, we have developed two fluorescence-based systems to monitor peroxisome-ER interactions. We modified a proximity ligation assay and a split-fluorescence reporter system using split superfolder green fluorescent protein. Using the proximity ligation assay we were able to measure changes in peroxisome-ER interactions whilst the split-fluorescence reporter was more limited and only allowed us to label ER-peroxisome contacts. We show that both techniques can be useful additions to the toolkit of methods to study peroxisome-ER associations and explore the relative merits of each.

Cardiovascular Effects and Molecular Mechanisms of Bisphenol A and Its Metabolite MBP in Zebrafish.

The plastic monomer bisphenol A (BPA) is one of the highest production volume chemicals in the world and is frequently detected in wildlife and humans, particularly children. BPA has been associated with numerous adverse health outcomes relating to its estrogenic and other hormonal properties, but direct causal links are unclear in humans and animal models. Here we simulated measured (1×) and predicted worst-case (10× ) maximum fetal exposures for BPA, or equivalent concentrations of its metabolite MBP, using fluorescent reporter embryo-larval zebrafish, capable of quantifying Estrogen Response Element (ERE) activation throughout the body. Heart valves were primary sites for ERE activation by BPA and MBP, and transcriptomic analysis of microdissected heart tissues showed that both chemicals targeted several molecular pathways constituting biomarkers for calcific aortic valve disease (CAVD), including extra-cellular matrix (ECM) alteration. ECM collagen deficiency and impact on heart valve structural integrity were confirmed by histopathology for high-level MBP exposure, and structural defects (abnormal curvature) of the atrio-ventricular valves corresponded with impaired cardiovascular function (reduced ventricular beat rate and blood flow). Our results are the first to demonstrate plausible mechanistic links between ERE activation in the heart valves by BPA's reactive metabolite MBP and the development of valvular-cardiovascular disease states.

Gold nanoparticles ingested by oyster larvae are internalized by cells through an alimentary endocytic pathway.

The biological fate of nanoparticles (NPs) taken up by organisms from their environment is a crucial issue for assessing ecological hazard. Despite its importance, it has scarcely been addressed due to the technical difficulties of doing so in whole organism in vivo studies. Here, by using transmission electron microscopy and energy dispersive X-ray spectroscopy (TEM-EDS), we describe the key aspects that characterize the interaction between an aquatic organism of global ecological and economic importance, the early larval stage of the Japanese oyster (Crassostrea gigas), and model gold NPs dispersed in their environment. The small size of the model organism allowed for a high-throughput visualization of the subcellular distribution of NPs, providing a comprehensive and robust picture of the route of uptake, mechanism of cellular permeation, and the pathways of clearance counterbalancing bioaccumulation. We show that NPs are ingested by larvae and penetrate cells through alimentary pinocytic/phagocytic mechanisms. They undergo intracellular digestion and storage inside residual bodies, before excretion with feces or translocation to phagocytic coelomocytes of the visceral cavity for potential extrusion or further translocation. Our mechanistically-supported findings highlight the potential of oyster larvae and other organisms which feature intracellular digestion processes to be exposed to man-made NPs and thus any risks associated with their inherent toxicity.

A single fungal MAP kinase controls plant cell-to-cell invasion by the rice blast fungus.

Blast disease destroys up to 30% of the rice crop annually and threatens global food security. The blast fungus Magnaporthe oryzae invades plant tissue with hyphae that proliferate and grow from cell to cell, often through pit fields, where plasmodesmata cluster. We showed that chemical genetic inhibition of a single fungal mitogen-activated protein (MAP) kinase, Pmk1, prevents M. oryzae from infecting adjacent plant cells, leaving the fungus trapped within a single plant cell. Pmk1 regulates expression of secreted fungal effector proteins implicated in suppression of host immune defenses, preventing reactive oxygen species generation and excessive callose deposition at plasmodesmata. Furthermore, Pmk1 controls the hyphal constriction required for fungal growth from one rice cell to the neighboring cell, enabling host tissue colonization and blast disease.

Dissolution and bandgap paradigms for predicting the toxicity of metal oxide nanoparticles in the marine environment: an in vivo study with oyster embryos.

Dissolution and bandgap paradigms have been proposed for predicting the ability of metal oxide nanoparticles (NPs) to induce oxidative stress in different in vitro and in vivo models. Here, we addressed the effectiveness of these paradigms in vivo and under conditions typical of the marine environment, a final sink for many NPs released through aquatic systems. We used ZnO and MnO2 NPs as models for dissolution and bandgap paradigms, respectively, and CeO2 NPs to assess reactive oxygen radical (ROS) production via Fenton-like reactions in vivo. Oyster embryos were exposed to 0.5-500 µM of each test NP over 24 h and oxidative stress was determined as a primary toxicity pathway across successive levels of biological complexity, with arrested development as the main pathological outcome. NPs were actively ingested by oyster larvae and entered cells. Dissolution was a viable paradigm for predicting the toxicity of NPs in the marine environment, whereas the surface reactivity based paradigms (i.e. bandgap and ROS generation via Fenton-like reaction) were not supported under seawater conditions. Bio-imaging identified potential cellular storage-disposal sites of solid particles that could ameliorate the toxicological behavior of non-dissolving NPs, whilst abiotic screening of surface reactivity suggested that the adsorption-complexation of surface active sites by seawater ions could provide a valuable hypothesis to explain the quenching of the intrinsic oxidation potential of MnO2 NPs in seawater.