Widespread phytoplankton blooms triggered by 2019-2020 Australian wildfires.

Droughts and climate-change-driven warming are leading to more frequent and intense wildfires1-3, arguably contributing to the severe 2019-2020 Australian wildfires4. The environmental and ecological impacts of the fires include loss of habitats and the emission of substantial amounts of atmospheric aerosols5-7. Aerosol emissions from wildfires can lead to the atmospheric transport of macronutrients and bio-essential trace metals such as nitrogen and iron, respectively8-10. It has been suggested that the oceanic deposition of wildfire aerosols can relieve nutrient limitations and, consequently, enhance marine productivity11,12, but direct observations are lacking. Here we use satellite and autonomous biogeochemical Argo float data to evaluate the effect of 2019-2020 Australian wildfire aerosol deposition on phytoplankton productivity. We find anomalously widespread phytoplankton blooms from December 2019 to March 2020 in the Southern Ocean downwind of Australia. Aerosol samples originating from the Australian wildfires contained a high iron content and atmospheric trajectories show that these aerosols were likely to be transported to the bloom regions, suggesting that the blooms resulted from the fertilization of the iron-limited waters of the Southern Ocean. Climate models project more frequent and severe wildfires in many regions1-3. A greater appreciation of the links between wildfires, pyrogenic aerosols13, nutrient cycling and marine photosynthesis could improve our understanding of the contemporary and glacial-interglacial cycling of atmospheric CO2 and the global climate system.

Microbiota regulate social behaviour via stress response neurons in the brain.

Social interactions among animals mediate essential behaviours, including mating, nurturing, and defence1,2. The gut microbiota contribute to social activity in mice3,4, but the gut-brain connections that regulate this complex behaviour and its underlying neural basis are unclear5,6. Here we show that the microbiome modulates neuronal activity in specific brain regions of male mice to regulate canonical stress responses and social behaviours. Social deviation in germ-free and antibiotic-treated mice is associated with elevated levels of the stress hormone corticosterone, which is primarily produced by activation of the hypothalamus-pituitary-adrenal (HPA) axis. Adrenalectomy, antagonism of glucocorticoid receptors, or pharmacological inhibition of corticosterone synthesis effectively corrects social deficits following microbiome depletion. Genetic ablation of glucocorticoid receptors in specific brain regions or chemogenetic inactivation of neurons in the paraventricular nucleus of the hypothalamus that produce corticotrophin-releasing hormone (CRH) reverse social impairments in antibiotic-treated mice. Conversely, specific activation of CRH-expressing neurons in the paraventricular nucleus induces social deficits in mice with a normal microbiome. Via microbiome profiling and in vivo selection, we identify a bacterial species, Enterococcus faecalis, that promotes social activity and reduces corticosterone levels in mice following social stress. These studies suggest that specific gut bacteria can restrain the activation of the HPA axis, and show that the microbiome can affect social behaviours through discrete neuronal circuits that mediate stress responses in the brain.

Functional and Immunologic Mapping of Domains of the Reticulocyte-Binding Protein Plasmodium vivax PvRBP2a.

We previously described a novel Plasmodium vivax invasion mechanism into human reticulocytes via the PvRBP2a-CD98 receptor-ligand pair. Using linear epitope mapping, we assessed the PvRBP2a epitopes involved in CD98 binding and recognized by antibodies from patients who were infected. We identified 2 epitope clusters mediating PvRBP2a-CD98 interaction. Cluster B (PvRBP2a431-448, TAALKEKGKLLANLYNKL) was the target of antibody responses in humans infected by P vivax. Peptides from each cluster were able to prevent live parasite invasion of human reticulocytes. These results provide new insights for development of a malaria blood-stage vaccine against P vivax.

A single-plasmid approach for genome editing coupled with long-term lineage analysis in chick embryos.

An important strategy for establishing mechanisms of gene function during development is through mutation of individual genes and analysis of subsequent effects on cell behavior. Here, we present a single-plasmid approach for genome editing in chick embryos to study experimentally perturbed cells in an otherwise normal embryonic environment. To achieve this, we have engineered a plasmid that encodes Cas9 protein, gene-specific guide RNA (gRNA), and a fluorescent marker within the same construct. Using transfection- and electroporation-based approaches, we show that this construct can be used to perturb gene function in early embryos as well as human cell lines. Importantly, insertion of this cistronic construct into replication-incompetent avian retroviruses allowed us to couple gene knockouts with long-term lineage analysis. We demonstrate the application of our newly engineered constructs and viruses by perturbing ß-catenin in vitro and Sox10, Pax6 and Pax7 in the neural crest, retina, and neural tube and segmental plate in vivo, respectively. Together, this approach enables genes of interest to be knocked out in identifiable cells in living embryos and can be broadly applied to numerous genes in different embryonic tissues.

Neural crest lineage analysis: from past to future trajectory.

Since its discovery 150 years ago, the neural crest has intrigued investigators owing to its remarkable developmental potential and extensive migratory ability. Cell lineage analysis has been an essential tool for exploring neural crest cell fate and migration routes. By marking progenitor cells, one can observe their subsequent locations and the cell types into which they differentiate. Here, we review major discoveries in neural crest lineage tracing from a historical perspective. We discuss how advancing technologies have refined lineage-tracing studies, and how clonal analysis can be applied to questions regarding multipotency. We also highlight how effective progenitor cell tracing, when combined with recently developed molecular and imaging tools, such as single-cell transcriptomics, single-molecule fluorescence in situ hybridization and high-resolution imaging, can extend the scope of neural crest lineage studies beyond development to regeneration and cancer initiation.

Macropinocytosis-mediated membrane recycling drives neural crest migration by delivering F-actin to the lamellipodium.

Individual cell migration requires front-to-back polarity manifested by lamellipodial extension. At present, it remains debated whether and how membrane motility mediates this cell morphological change. To gain insights into these processes, we perform live imaging and molecular perturbation of migrating chick neural crest cells in vivo. Our results reveal an endocytic loop formed by circular membrane flow and anterograde movement of lipid vesicles, resulting in cell polarization and locomotion. Rather than clathrin-mediated endocytosis, macropinosomes encapsulate F-actin in the cell body, forming vesicles that translocate via microtubules to deliver actin to the anterior. In addition to previously proposed local conversion of actin monomers to polymers, we demonstrate a surprising role for shuttling of F-actin across cells for lamellipodial expansion. Thus, the membrane and cytoskeleton act in concert in distinct subcellular compartments to drive forward cell migration.

RARγ is required for mesodermal gene expression prior to gastrulation in Xenopus.

The developing vertebrate embryo is exquisitely sensitive to retinoic acid (RA) concentration, particularly during anteroposterior patterning. In contrast to Nodal and Wnt signaling, RA was not previously considered to be an instructive signal in mesoderm formation during gastrulation. Here, we show in Xenopus that RARγ is indispensable for the expression of early mesoderm markers and is, therefore, an obligatory factor in mesodermal competence and/or maintenance. We identified several novel targets upregulated by RA receptor signaling in the early gastrula that are expressed in the circumblastoporal ring and linked to mesodermal development. Despite overlapping expression patterns of the genes encoding the RA-synthesizing enzyme Aldh1a2 and the RA-degrading enzyme Cyp26a1, RARγ1 functions as a transcriptional activator in early mesoderm development, suggesting that RA ligand is available to the embryo earlier than previously appreciated. RARγ1 is required for cellular adhesion, as revealed by spontaneous dissociation and depletion of ncam1 mRNA in animal caps harvested from RARγ1 knockdown embryos. RARγ1 knockdown obliterates somite boundaries, and causes loss of Myod protein in the presomitic mesoderm, but ectopic, persistent expression of Myod protein in the trunk. Thus, RARγ1 is required for stabilizing the mesodermal fate, myogenic commitment, somite boundary formation, and terminal skeletal muscle differentiation.

Suitability of Nansha Mangrove Wetland for High Nitrogen Shrimp Pond Wastewater Treatment.

To investigate mangroves of different land use types in Nansha county, China, we analyzed the corresponding N2O and CH4 emissions, water temperature, salinity, acidity and alkalinity, dissolved oxygen, redox potential, nitrate, nitrite, ammonia nitrogen, and organic matter at five sites. The removal rates of NO2-, NO3-, and NH4+ in mangrove wetlands were 43.6%, 41.2%, and 65.0%; however, CH4 and N2O emissions of mangrove affected by shrimp ponds are 2-3 times and 3-9 times more high than other wetlands. These results showed that, although mangrove wetlands can significantly reduce N, P, and other nutrient elements in shrimp pond wastewater, they can also significantly increase N2O and CH4 emissions. This indicates that mangrove wetlands should be used with caution for the treatment of shrimp pond wastewater.

Multiplex clonal analysis in the chick embryo using retrovirally-mediated combinatorial labeling.

Lineage analysis plays a central role in exploring the developmental potential of stem and progenitor cell populations. In higher vertebrates, a variety of techniques have been used to label individual cells or cell populations, including interspecies grafting, intracellular microinjection, and Cre-mediated recombination. However, these approaches often suffer from difficulties in progenitor cell targeting, low cellular resolution and/or ectopic labeling. To circumvent these issues, here we utilize replication incompetent avian (RIA) retroviruses to deliver combinations of fluorescent proteins into distinct cellular compartments in chick embryos. In particular, RIA-mediated lineage tracing is optimal for long term mapping of dispersing cell populations like the neural crest. Using this tool, we confirm that trunk neural crest cells are multipotent. Furthermore, our RIA vector is engineered to be fully adaptable for other purposes such as cell fate analysis, gene perturbation studies and time-lapse imaging. Taken together, we present a novel approach of multiplex lineage analysis that can be applied to normal and perturbed development of diverse cell populations in avian embryos.

RARß2 is required for vertebrate somitogenesis.

During vertebrate somitogenesis, retinoic acid is known to establish the position of the determination wavefront, controlling where new somites are permitted to form along the anteroposterior body axis. Less is understood about how RAR regulates somite patterning, rostral-caudal boundary setting, specialization of myotome subdivisions or the specific RAR subtype that is required for somite patterning. Characterizing the function of RARß has been challenging due to the absence of embryonic phenotypes in murine loss-of-function studies. Using the Xenopus system, we show that RARß2 plays a specific role in somite number and size, restriction of the presomitic mesoderm anterior border, somite chevron morphology and hypaxial myoblast migration. Rarß2 is the RAR subtype whose expression is most upregulated in response to ligand and its localization in the trunk somites positions it at the right time and place to respond to embryonic retinoid levels during somitogenesis. RARß2 positively regulates Tbx3 a marker of hypaxial muscle, and negatively regulates Tbx6 via Ripply2 to restrict the anterior boundaries of the presomitic mesoderm and caudal progenitor pool. These results demonstrate for the first time an early and essential role for RARß2 in vertebrate somitogenesis.

Method for High Frequency Underway N2 Fixation Measurements: Flow-Through Incubation Acetylene Reduction Assays by Cavity Ring Down Laser Absorption Spectroscopy (FARACAS).

Because of the difficulty in resolving the large variability of N2 fixation with current methods which rely on discrete sampling, the development of new methods for high-resolution measurements is highly desirable. We present a new method for high-frequency measurements of aquatic N2 fixation by continuous flow-through incubations and spectral monitoring of the acetylene (C2H2, a substrate analog for N2) reduction to ethylene (C2H4). In this method, named Flow-through Incubation Acetylene Reduction Assays by Cavity Ring-Down Laser Absorption Spectroscopy (FARACAS), dissolved C2H2 is continuously admixed with seawater upstream of a continuous-flow stirred-tank reactor (CFSR) in which C2H2 reduction takes place. Downstream of the flow-through incubator, the C2H4 gas is stripped using a bubble column contactor and circulated with a diaphragm pump into a wavelength-scanned cavity ring down laser absorption spectrometer (CRDS). Our method provides high-resolution and precise mapping of aquatic N2 fixation, its diel cycle, and its response to environmental gradients, and can be adapted to measure other biological processes. The short-duration of the flow-through incubations without preconcentration of cells minimizes potential artifacts such as bottle containment effects while providing near real-time estimates for adaptive sampling. We expect that our new method will improve the characterization of the biogeography and kinetics of aquatic N2 fixation rates.

The unexpected teratogenicity of RXR antagonist UVI3003 via activation of PPARγ in Xenopus tropicalis.

The RXR agonist (triphenyltin, TPT) and the RXR antagonist (UVI3003) both show teratogenicity and, unexpectedly, induce similar malformations in Xenopus tropicalis embryos. In the present study, we exposed X. tropicalis embryos to UVI3003 in seven specific developmental windows and identified changes in gene expression. We further measured the ability of UVI3003 to activate Xenopus RXRα (xRXRα) and PPARγ (xPPARγ) in vitro and in vivo. We found that UVI3003 activated xPPARγ either in Cos7 cells (in vitro) or Xenopus embryos (in vivo). UVI3003 did not significantly activate human or mouse PPARγ in vitro; therefore, the activation of Xenopus PPARγ by UVI3003 is novel. The ability of UVI3003 to activate xPPARγ explains why UVI3003 and TPT yield similar phenotypes in Xenopus embryos. Our results indicate that activating PPARγ leads to teratogenic effects in Xenopus embryos. More generally, we infer that chemicals known to specifically modulate mammalian nuclear hormone receptors cannot be assumed to have the same activity in non-mammalian species, such as Xenopus. Rather they must be tested for activity and specificity on receptors of the species in question to avoid making inappropriate conclusions.

Interface Engineering to Drive High-Performance MXene/PbS Quantum Dot NIR Photodiode.

The realization of a controllable transparent conducting system with selective light transparency is crucial for exploring many of the most intriguing effects in top-illuminated optoelectronic devices. However, the performance is limited by insufficient electrical conductivity, low work function, and vulnerable interface of traditional transparent conducting materials, such as tin-doped indium oxide. Here, it is reported that two-dimensional (2D) titanium carbide (Ti3 C2 Tx ) MXene film acts as an efficient transparent conducting electrode for the lead sulfide (PbS) colloidal quantum dots (CQDs) photodiode with controllable near infrared transmittance. The solution-processed interface engineering of MXene and PbS layers remarkably reduces the interface defects of MXene/PbS CQDs and the carrier concentration in the PbS layer. The stable Ti3 C2 Tx /PbS CQDs photodiodes give rise to a high specific detectivity of 5.51 × 1012  cm W-1  Hz1/2 , a large dynamic response range of 140 dB, and a large bandwidth of 0.76 MHz at 940 nm in the self-powered state, ranking among the most exceptional in terms of comprehensive performance among reported PbS CQDs photodiodes. In contrast with the traditional photodiode technologies, this efficient and stable approach opens a new horizon to construct widely used infrared photodiodes with CQDs and MXenes.

An exceptional phytoplankton bloom in the southeast Madagascar Sea driven by African dust deposition.

Rising surface temperatures are projected to cause more frequent and intense droughts in the world's drylands. This can lead to land degradation, mobilization of soil particles, and an increase in dust aerosol emissions from arid and semi-arid regions. Dust aerosols are a key source of bio-essential nutrients, can be transported in the atmosphere over large distances, and ultimately deposited onto the ocean's surface, alleviating nutrient limitation and increasing oceanic primary productivity. Currently, the linkages between desertification, dust emissions and ocean fertilization remain poorly understood. Here, we show that dust emitted from Southern Africa was transported and deposited into the nutrient-limited surface waters southeast of Madagascar, which stimulated the strongest phytoplankton bloom of the last two decades during a period of the year when blooms are not expected. The conditions required for triggering blooms of this magnitude are anomalous, but current trends in air temperatures, aridity, and dust emissions in Southern Africa suggest that such events could become more probable in the future. Together with the recent findings on ocean fertilization by drought-induced megafires in Australia, our results point toward a potential link between global warming, drought, aerosol emissions, and ocean blooms.

Single-cell profiling coupled with lineage analysis reveals vagal and sacral neural crest contributions to the developing enteric nervous system.

During development, much of the enteric nervous system (ENS) arises from the vagal neural crest that emerges from the caudal hindbrain and colonizes the entire gastrointestinal tract. However, a second ENS contribution comes from the sacral neural crest that arises in the caudal neural tube and populates the post-umbilical gut. By coupling single-cell transcriptomics with axial-level-specific lineage tracing in avian embryos, we compared the contributions of embryonic vagal and sacral neural crest cells to the chick ENS and the associated peripheral ganglia (Nerve of Remak and pelvic plexuses). At embryonic day (E) 10, the two neural crest populations form overlapping subsets of neuronal and glia cell types. Surprisingly, the post-umbilical vagal neural crest much more closely resembles the sacral neural crest than the pre-umbilical vagal neural crest. However, some differences in cluster types were noted between vagal and sacral derived cells. Notably, RNA trajectory analysis suggests that the vagal neural crest maintains a neuronal/glial progenitor pool, whereas this cluster is depleted in the E10 sacral neural crest which instead has numerous enteric glia. The present findings reveal sacral neural crest contributions to the hindgut and associated peripheral ganglia and highlight the potential influence of the local environment and/or developmental timing in differentiation of neural crest-derived cells in the developing ENS.

Particle-associated denitrification is the primary source of N2O in oxic coastal waters.

The heavily human-perturbed coastal oceans are hotspots of nitrous oxide (N2O) emission to the atmosphere. The processes underpinning the N2O flux, however, remain poorly understood, leading to large uncertainties in assessing global N2O budgets. Using a suite of nitrogen isotope labeling experiments, we show that multiple processes contribute to N2O production throughout the estuarine-coastal gradient, sustaining intensive N2O flux to the atmosphere. Unexpectedly, denitrification, rather than ammonia oxidation as previously assumed, constitutes the major source of N2O in well-oxygenated coastal waters. Size-fractionated manipulation experiments with gene analysis further reveal niche partitioning of ammonia oxidizers and denitrifiers across the particle size spectrum; denitrification dominated on large particles and ammonia oxidizers on small particles. Total N2O production rate increases with substrate and particle concentrations, suggesting a crucial interplay between nutrients and particles in controlling N2O production. The controlling factors identified here may help understand climate feedback mechanisms between human activity and coastal oceans.

Self-concept clarity and Internet addiction disorder among junior high school students: A moderate mediation model.

Introduction: As the epidemic spreads, the problem of Internet addiction disorder (IAD) stand out and getting serious. The present study aimed to investigate IAD among junior high school students during the spread of the COVID-19, and to explore the mediating role of cognitive failure between self-concept clarity and IAD, and the moderating role of mindfulness. Methods: A sample of 1,153 junior high school students from two randomly selected junior high schools in Henan Province were surveyed anonymously with Self-concept Clarity Scale (SCCS), Cognitive Failure Questionnaire (CFQ), Mindfulness Attention Awareness Scale (MAAS) and Internet Addiction disorder Test (IAT). The sample was obtained through random cluster sampling, taking classes as the clusters and students as the elements. Results: (1) Self-concept clarity was negatively correlated with Internet addiction disorder; (2) Self-concept clarity not only had a direct effect on Internet addiction disorder, but also indirectly affect Internet addiction disorder through cognitive failure; (3) Mindfulness moderates the relationship between self-concept clarity and Internet addiction disorder, as well as the relationship between cognitive failure and Internet addiction disorder. Compared with low levels of mindfulness, both the protective effect of self-concept clarity and the effect of cognitive failure on Internet addiction disorder were stronger among junior high school students who were at high levels of mindfulness. Conclusion: This study constructs a moderated mediation model to explain the effect of self-concept clarity on Internet addiction disorder. It is effective to alleviate Internet addiction disorder by improving self-concept clarity and mindfulness level of the junior school students.

Regional Differences and Convergence of Urban-Rural Integration Development from the Perspective of Factor Flow.

Based on the panel data of thirty-one provinces in China from 2003 to 2020, we constructed an evaluation index system of urban-rural integration development level from the perspective of factor flow. The combined weighting model of GI and CRITIC were used to evaluate the regional urban-rural integration development. The coefficient of variation and panel fixed effect model was used to explore convergence, absolute convergence, and conditional convergence. The impact of capital, labor, and technology factor flow on the convergence of urban-rural integration development level was further investigated. In addition, the difference analysis in time scale and impulse response function analysis was performed to explore the regular pattern of factor flow on the convergence of urban-rural integration development. The main conclusions were as follows: first, the growth of urban-rural integration development had an absolute convergence trend and tended to conditional convergence faster. Second, the capital flow positively affected the convergence of urban-rural integration development, while labor and technology flow had a slowing effect on the convergence of urban-rural integration development at this stage. Third, the impact of factor flow on the convergence of urban-rural integration development was dissimilar during different phases. The convergence rate of urban-rural integration development after 2012 was drastically slower than before.

Phosphate limitation intensifies negative effects of ocean acidification on globally important nitrogen fixing cyanobacterium.

Growth of the prominent nitrogen-fixing cyanobacterium Trichodesmium is often limited by phosphorus availability in the ocean. How nitrogen fixation by phosphorus-limited Trichodesmium may respond to ocean acidification remains poorly understood. Here, we use phosphate-limited chemostat experiments to show that acidification enhanced phosphorus demands and decreased phosphorus-specific nitrogen fixation rates in Trichodesmium. The increased phosphorus requirements were attributed primarily to elevated cellular polyphosphate contents, likely for maintaining cytosolic pH homeostasis in response to acidification. Alongside the accumulation of polyphosphate, decreased NADP(H):NAD(H) ratios and impaired chlorophyll synthesis and energy production were observed under acidified conditions. Consequently, the negative effects of acidification were amplified compared to those demonstrated previously under phosphorus sufficiency. Estimating the potential implications of this finding, using outputs from the Community Earth System Model, predicts that acidification and dissolved inorganic and organic phosphorus stress could synergistically cause an appreciable decrease in global Trichodesmium nitrogen fixation by 2100.