Oxygen-evolving photosystem II structures during S1-S2-S3 transitions.

Photosystem II (PSII) catalyses the oxidation of water through a four-step cycle of Si states (i = 0-4) at the Mn4CaO5 cluster1-3, during which an extra oxygen (O6) is incorporated at the S3 state to form a possible dioxygen4-7. Structural changes of the metal cluster and its environment during the S-state transitions have been studied on the microsecond timescale. Here we use pump-probe serial femtosecond crystallography to reveal the structural dynamics of PSII from nanoseconds to milliseconds after illumination with one flash (1F) or two flashes (2F). YZ, a tyrosine residue that connects the reaction centre P680 and the Mn4CaO5 cluster, showed structural changes on a nanosecond timescale, as did its surrounding amino acid residues and water molecules, reflecting the fast transfer of electrons and protons after flash illumination. Notably, one water molecule emerged in the vicinity of Glu189 of the D1 subunit of PSII (D1-E189), and was bound to the Ca2+ ion on a sub-microsecond timescale after 2F illumination. This water molecule disappeared later with the concomitant increase of O6, suggesting that it is the origin of O6. We also observed concerted movements of water molecules in the O1, O4 and Cl-1 channels and their surrounding amino acid residues to complete the sequence of electron transfer, proton release and substrate water delivery. These results provide crucial insights into the structural dynamics of PSII during S-state transitions as well as O-O bond formation.

Cyclic nucleotide-induced bidirectional long-term synaptic plasticity in Drosophila mushroom body.

Activation of the cAMP pathway is one of the common mechanisms underlying long-term potentiation (LTP). In the Drosophila mushroom body, simultaneous activation of odour-coding Kenyon cells (KCs) and reinforcement-coding dopaminergic neurons activates adenylyl cyclase in KC presynaptic terminals, which is believed to trigger synaptic plasticity underlying olfactory associative learning. However, learning induces long-term depression (LTD) at these synapses, contradicting the universal role of cAMP as a facilitator of transmission. Here, we developed a system to electrophysiologically monitor both short-term and long-term synaptic plasticity at KC output synapses and demonstrated that they are indeed an exception in which activation of the cAMP-protein kinase A pathway induces LTD. Contrary to the prevailing model, our cAMP imaging found no evidence for synergistic action of dopamine and KC activity on cAMP synthesis. Furthermore, we found that forskolin-induced cAMP increase alone was insufficient for plasticity induction; it additionally required simultaneous KC activation to replicate the presynaptic LTD induced by pairing with dopamine. On the other hand, activation of the cGMP pathway paired with KC activation induced slowly developing LTP, proving antagonistic actions of the two second-messenger pathways predicted by behavioural study. Finally, KC subtype-specific interrogation of synapses revealed that different KC subtypes exhibit distinct plasticity duration even among synapses on the same postsynaptic neuron. Thus, our work not only revises the role of cAMP in synaptic plasticity by uncovering the unexpected convergence point of the cAMP pathway and neuronal activity, but also establishes the methods to address physiological mechanisms of synaptic plasticity in this important model. KEY POINTS: Although presynaptic cAMP increase generally facilitates synapses, olfactory associative learning in Drosophila, which depends on dopamine and cAMP signalling genes, induces long-term depression (LTD) at the mushroom body output synapses. By combining electrophysiology, pharmacology and optogenetics, we directly demonstrate that these synapses are an exception where activation of the cAMP-protein kinase A pathway leads to presynaptic LTD. Dopamine- or forskolin-induced cAMP increase alone is not sufficient for LTD induction; neuronal activity, which has been believed to trigger cAMP synthesis in synergy with dopamine input, is required in the downstream pathway of cAMP. In contrast to cAMP, activation of the cGMP pathway paired with neuronal activity induces presynaptic long-term potentiation, which explains behaviourally observed opposing actions of transmitters co-released by dopaminergic neurons. Our work not only revises the role of cAMP in synaptic plasticity, but also provides essential methods to address physiological mechanisms of synaptic plasticity in this important model system.

Short-lived intermediate in N2O generation by P450 NO reductase captured by time-resolved IR spectroscopy and XFEL crystallography.

Nitric oxide (NO) reductase from the fungus Fusarium oxysporum is a P450-type enzyme (P450nor) that catalyzes the reduction of NO to nitrous oxide (N2O) in the global nitrogen cycle. In this enzymatic reaction, the heme-bound NO is activated by the direct hydride transfer from NADH to generate a short-lived intermediate ( I ), a key state to promote N-N bond formation and N-O bond cleavage. This study applied time-resolved (TR) techniques in conjunction with photolabile-caged NO to gain direct experimental results for the characterization of the coordination and electronic structures of I TR freeze-trap crystallography using an X-ray free electron laser (XFEL) reveals highly bent Fe-NO coordination in I , with an elongated Fe-NO bond length (Fe-NO = 1.91 Å, Fe-N-O = 138°) in the absence of NAD+ TR-infrared (IR) spectroscopy detects the formation of I with an N-O stretching frequency of 1,290 cm-1 upon hydride transfer from NADH to the Fe3+-NO enzyme via the dissociation of NAD+ from a transient state, with an N-O stretching of 1,330 cm-1 and a lifetime of ca. 16 ms. Quantum mechanics/molecular mechanics calculations, based on these crystallographic and IR spectroscopic results, demonstrate that the electronic structure of I is characterized by a singly protonated Fe3+-NHO•- radical. The current findings provide conclusive evidence for the N2O generation mechanism via a radical-radical coupling of the heme nitroxyl complex with the second NO molecule.

Structural Changes during the Photorepair and Binding Processes of Xenopus (6-4) Photolyase with (6-4) Photoproducts in Single- and Double-Stranded DNA.

Photolyases (PHRs) repair ultraviolet (UV)-induced DNA photoproducts into normal bases. In this study, we measured the conformational changes upon photoactivation and photorepair processes of a PHR and its specific substrates, (6-4)PHR and a pyrimidine(6-4)pyrimidone photoproduct ((6-4)PP), by light-induced difference Fourier transform infrared (FT-IR) spectroscopy. The single-stranded DNA with (6-4)PP (ss(6-4)PP) was used as a substrate and the resultant FT-IR spectra were compared with the previous results on double-stranded DNA with (6-4)PP (ds(6-4)PP). In the excess amount of substrate to the enzyme, different ss(6-4)PP photorepair FT-IR signals were obtained in an illumination time-dependent manner. As reported for ds(6-4)PP, the early stages of the photoreaction involve the changes in the ss(6-4)PP only, while the late stages of the reaction involve the ss(6-4)PP repair-associated changes and dissociation from (6-4)PHR. From these spectra, difference spectra originating from the binding/dissociation spectrum were extracted. The signals of the C═O stretches of (6-4)PP and repaired thymines in the single- and double-stranded DNA were tentatively assigned. The C═O stretches of (6-4)PP were observed at frequencies that reflect single- and double-stranded DNA environments in aqueous solution, reflecting the different hydrogen-bonding environments. The conformational changes of PHR upon binding of ss(6-4)PP and ds(6-4)PP were similar, suggesting that the conformational change is limited to the (6-4)PP binding pocket region. We interpreted that ds(6-4)PP may be bound together without any special mechanism for flipping out.

Spectroscopic study of the transmembrane domain of a rhodopsin-phosphodiesterase fusion protein from a unicellular eukaryote.

The choanoflagellate Salpingoeca rosetta contains a chimeric rhodopsin protein composed of an N-terminal rhodopsin (Rh) domain and a C-terminal cyclic nucleotide phosphodiesterase (PDE) domain. The Rh-PDE enzyme light-dependently decreases the concentrations of cyclic nucleotides such as cGMP and cAMP. Photoexcitation of purified full-length Rh-PDE yields an "M" intermediate with a deprotonated Schiff base, and its recovery is much faster than that of the enzyme domain. To gain structural and mechanistic insights into the Rh domain, here we expressed and purified the transmembrane domain of Rh-PDE, Rh-PDE(TMD), and analyzed it with transient absorption, light-induced difference UV-visible, and FTIR spectroscopy methods. These analyses revealed that the "K" intermediate forms within 0.005 ms and converts into the M intermediate with a time constant of 4 ms, with the latter returning to the original state within 4 s. FTIR spectroscopy revealed that all-trans to 13-cis photoisomerization occurs as the primary event during which chromophore distortion is located at the middle of the polyene chain, allowing the Schiff base to form a stronger hydrogen bond. We also noted that the peptide backbone of the α-helix becomes deformed upon M intermediate formation. Results from site-directed mutagenesis suggested that Glu-164 is protonated and that Asp-292 acts as the only Schiff base counterion in Rh-PDE. A strong reduction of enzymatic activity in a D292N variant, but not in an E164Q variant, indicated an important catalytic role of the negative charge at Asp-292. Our findings provide further mechanistic insights into rhodopsin-mediated, light-dependent regulation of second-messenger levels in eukaryotic microbes.

ATP binding promotes light-induced structural changes to the protein moiety of Arabidopsis cryptochrome 1.

Cryptochromes (CRYs) are blue-light receptors involved in photomorphogenesis in plants. Flavin adenine dinucleotide (FAD) is one of the chromophores of cryptochromes; its resting state oxidized form is converted into a signalling state neutral semiquionod radical (FADH˙) form. Studies have shown that cryptochrome 1 from Arabidopsis thaliana (AtCRY1) can bind ATP at its photolyase homology region (PHR), resulting in accumulation of FADH˙ form. This study used light-induced difference Fourier transform infrared spectroscopy to investigate how ATP influences structural changes in AtCRY1-PHR during the photoreaction. In the presence of ATP, there were large changes in the signals from the protein backbone compared with in the absence of ATP. The deprotonation of a carboxylic acid was observed only in the presence of ATP; this was assigned as aspartic acid (Asp) 396 through measurement of Asp to glutamic acid mutants. This corresponds to the protonation state of Asp396 estimated from the reported pKa values of Asp396; that is, the side chain of Asp396 is deprotonated and protonated for the ATP-free and -bound forms, respectively, in our experimental condition at pH8. Therefore, Asp396 acts a proton donor to FAD when it is ptotonated. It was indicated that the protonation/deprotination process of Asp396 is correlated with the accunumulation of FADH˙ and protein conformational changes.

GABAergic Local Interneurons Shape Female Fruit Fly Response to Mating Songs.

Many animals use acoustic signals to attract a potential mating partner. In fruit flies (Drosophila melanogaster), the courtship pulse song has a species-specific interpulse interval (IPI) that activates mating. Although a series of auditory neurons in the fly brain exhibit different tuning patterns to IPIs, it is unclear how the response of each neuron is tuned. Here, we studied the neural circuitry regulating the activity of antennal mechanosensory and motor center (AMMC)-B1 neurons, key secondary auditory neurons in the excitatory neural pathway that relay song information. By performing Ca2+ imaging in female flies, we found that the IPI selectivity observed in AMMC-B1 neurons differs from that of upstream auditory sensory neurons [Johnston's organ (JO)-B]. Selective knock-down of a GABAA receptor subunit in AMMC-B1 neurons increased their response to short IPIs, suggesting that GABA suppresses AMMC-B1 activity at these IPIs. Connection mapping identified two GABAergic local interneurons that synapse with AMMC-B1 and JO-B. Ca2+ imaging combined with neuronal silencing revealed that these local interneurons, AMMC-LN and AMMC-B2, shape the response pattern of AMMC-B1 neurons at a 15 ms IPI. Neuronal silencing studies further suggested that both GABAergic local interneurons suppress the behavioral response to artificial pulse songs in flies, particularly those with a 15 ms IPI. Altogether, we identified a circuit containing two GABAergic local interneurons that affects the temporal tuning of AMMC-B1 neurons in the song relay pathway and the behavioral response to the courtship song. Our findings suggest that feedforward inhibitory pathways adjust the behavioral response to courtship pulse songs in female flies.SIGNIFICANCE STATEMENT To understand how the brain detects time intervals between sound elements, we studied the neural pathway that relays species-specific courtship song information in female Drosophila melanogaster We demonstrate that the signal transmission from auditory sensory neurons to key secondary auditory neurons antennal mechanosensory and motor center (AMMC)-B1 is the first-step to generate time interval selectivity of neurons in the song relay pathway. Two GABAergic local interneurons are suggested to shape the interval selectivity of AMMC-B1 neurons by receiving auditory inputs and in turn providing feedforward inhibition onto AMMC-B1 neurons. Furthermore, these GABAergic local interneurons suppress the song response behavior in an interval-dependent manner. Our results provide new insights into the neural circuit basis to adjust neuronal and behavioral responses to a species-specific communication sound.

VaProS: a database-integration approach for protein/genome information retrieval.

Life science research now heavily relies on all sorts of databases for genome sequences, transcription, protein three-dimensional (3D) structures, protein-protein interactions, phenotypes and so forth. The knowledge accumulated by all the omics research is so vast that a computer-aided search of data is now a prerequisite for starting a new study. In addition, a combinatory search throughout these databases has a chance to extract new ideas and new hypotheses that can be examined by wet-lab experiments. By virtually integrating the related databases on the Internet, we have built a new web application that facilitates life science researchers for retrieving experts' knowledge stored in the databases and for building a new hypothesis of the research target. This web application, named VaProS, puts stress on the interconnection between the functional information of genome sequences and protein 3D structures, such as structural effect of the gene mutation. In this manuscript, we present the notion of VaProS, the databases and tools that can be accessed without any knowledge of database locations and data formats, and the power of search exemplified in quest of the molecular mechanisms of lysosomal storage disease. VaProS can be freely accessed at http://p4d-info.nig.ac.jp/vapros/ .

Structural Changes of the Active Center during the Photoactivation of Xenopus (6-4) Photolyase.

Photolyases (PHRs) repair the UV-induced photoproducts, cyclobutane pyrimidine dimer (CPD) or pyrimidine-pyrimidone (6-4) photoproduct [(6-4) PP], restoring normal bases to maintain genetic integrity. CPD and (6-4) PP are repaired by substrate-specific PHRs, CPD PHR and (6-4) PHR, respectively. Flavin adenine dinucleotide (FAD) is the chromophore of both PHRs, and the resting oxidized form (FAD(ox)), at least under in vitro purified conditions, is first photoconverted to the neutral semiquinoid radical (FADH(•)) form, followed by photoconversion into the enzymatically active fully reduced (FADH(-)) form. Previously, we reported light-induced difference Fourier transform infrared (FTIR) spectra corresponding to the photoactivation process of Xenopus (6-4) PHR. Spectral differences between the absence and presence of (6-4) PP were observed in the photoactivation process. To identify the FTIR signals where these differences appeared, we compared the FTIR spectra of photoactivation (i) in the presence and absence of (6-4) PP, (ii) of (13)C labeling, (15)N labeling, and [(14)N]His/(15)N labeling, and (iii) of H354A and H358A mutants. We successfully assigned the vibrational bands for (6-4) PP, the α-helix and neutral His residue(s). In particular, we assigned three bands to the C ═ O groups of (6-4) PP in the three different redox states of FAD. Furthermore, the changed hydrogen bonding environments of C ═ O groups of (6-4) PP suggested restructuring of the binding pocket of the DNA lesion in the process of photoactivation.

Functional Conversion of CPD and (6-4) Photolyases by Mutation.

Ultraviolet (UV) light from the sun damages DNA by forming a cyclobutane pyrimidine dimer (CPD) and pyrimidine(6-4)pyrimidone photoproducts [(6-4) PP]. Photolyase (PHR) enzymes utilize near-UV/blue light for DNA repair, which is initiated by light-induced electron transfer from the fully reduced flavin adenine dinucleotide chromophore. Despite similar structures and repair mechanisms, the functions of PHR are highly selective; CPD PHR repairs CPD, but not (6-4) PP, and vice versa. In this study, we attempted functional conversion between CPD and (6-4) PHRs. We found that a triple mutant of (6-4) PHR is able to repair the CPD photoproduct, though the repair efficiency is 1 order of magnitude lower than that of wild-type CPD PHR. Difference Fourier transform infrared spectra for repair demonstrate the lack of secondary structural alteration in the mutant, suggesting that the triple mutant gains substrate binding ability while it does not gain the optimized conformational changes from light-induced electron transfer to the release of the repaired DNA. Interestingly, the (6-4) photoproduct is not repaired by the reverse mutation of CPD PHR, and eight additional mutations (total of 11 mutations) introduced into CPD PHR are not sufficient. The observed asymmetric functional conversion is interpreted in terms of a more complex repair mechanism for (6-4) repair, which was supported by quantum chemical/molecular mechanical calculation. These results suggest that CPD PHR may represent an evolutionary origin for photolyase family proteins.

Cyclic nucleotide-induced bidirectional long-term synaptic plasticity in Drosophila mushroom body.

Activation of the cAMP pathway is one of the common mechanisms underlying long-term potentiation (LTP). In the Drosophila mushroom body, simultaneous activation of odor-coding Kenyon cells (KCs) and reinforcement-coding dopaminergic neurons activates adenylyl cyclase in KC presynaptic terminals, which is believed to trigger synaptic plasticity underlying olfactory associative learning. However, learning induces long-term depression (LTD) at these synapses, contradicting the universal role of cAMP as a facilitator of transmission. Here, we develop a system to electrophysiologically monitor both short-term and long-term synaptic plasticity at KC output synapses and demonstrate that they are indeed an exception where activation of the cAMP/protein kinase A pathway induces LTD. Contrary to the prevailing model, our cAMP imaging finds no evidence for synergistic action of dopamine and KC activity on cAMP synthesis. Furthermore, we find that forskolin-induced cAMP increase alone is insufficient for plasticity induction; it additionally requires simultaneous KC activation to replicate the presynaptic LTD induced by pairing with dopamine. On the other hand, activation of the cGMP pathway paired with KC activation induces slowly developing LTP, proving antagonistic actions of the two second-messenger pathways predicted by behavioral study. Finally, KC subtype-specific interrogation of synapses reveals that different KC subtypes exhibit distinct plasticity duration even among synapses on the same postsynaptic neuron. Thus, our work not only revises the role of cAMP in synaptic plasticity by uncovering the unexpected convergence point of the cAMP pathway and neuronal activity, but also establishes the methods to address physiological mechanisms of synaptic plasticity in this important model.

A lightweight data-driven spiking neuronal network model of Drosophila olfactory nervous system with dedicated hardware support.

Data-driven spiking neuronal network (SNN) models enable in-silico analysis of the nervous system at the cellular and synaptic level. Therefore, they are a key tool for elucidating the information processing principles of the brain. While extensive research has focused on developing data-driven SNN models for mammalian brains, their complexity poses challenges in achieving precision. Network topology often relies on statistical inference, and the functions of specific brain regions and supporting neuronal activities remain unclear. Additionally, these models demand huge computing facilities and their simulation speed is considerably slower than real-time. Here, we propose a lightweight data-driven SNN model that strikes a balance between simplicity and reproducibility. The model is built using a qualitative modeling approach that can reproduce key dynamics of neuronal activity. We target the Drosophila olfactory nervous system, extracting its network topology from connectome data. The model was successfully implemented on a small entry-level field-programmable gate array and simulated the activity of a network in real-time. In addition, the model reproduced olfactory associative learning, the primary function of the olfactory system, and characteristic spiking activities of different neuron types. In sum, this paper propose a method for building data-driven SNN models from biological data. Our approach reproduces the function and neuronal activities of the nervous system and is lightweight, acceleratable with dedicated hardware, making it scalable to large-scale networks. Therefore, our approach is expected to play an important role in elucidating the brain's information processing at the cellular and synaptic level through an analysis-by-construction approach. In addition, it may be applicable to edge artificial intelligence systems in the future.

Neural circuit mechanisms for transforming learned olfactory valences into wind-oriented movement.

How memories are used by the brain to guide future action is poorly understood. In olfactory associative learning in Drosophila, multiple compartments of the mushroom body act in parallel to assign a valence to a stimulus. Here, we show that appetitive memories stored in different compartments induce different levels of upwind locomotion. Using a photoactivation screen of a new collection of split-GAL4 drivers and EM connectomics, we identified a cluster of neurons postsynaptic to the mushroom body output neurons (MBONs) that can trigger robust upwind steering. These UpWind Neurons (UpWiNs) integrate inhibitory and excitatory synaptic inputs from MBONs of appetitive and aversive memory compartments, respectively. After formation of appetitive memory, UpWiNs acquire enhanced response to reward-predicting odors as the response of the inhibitory presynaptic MBON undergoes depression. Blocking UpWiNs impaired appetitive memory and reduced upwind locomotion during retrieval. Photoactivation of UpWiNs also increased the chance of returning to a location where activation was terminated, suggesting an additional role in olfactory navigation. Thus, our results provide insight into how learned abstract valences are gradually transformed into concrete memory-driven actions through divergent and convergent networks, a neuronal architecture that is commonly found in the vertebrate and invertebrate brains.

Hierarchical architecture of dopaminergic circuits enables second-order conditioning in Drosophila.

Dopaminergic neurons with distinct projection patterns and physiological properties compose memory subsystems in a brain. However, it is poorly understood whether or how they interact during complex learning. Here, we identify a feedforward circuit formed between dopamine subsystems and show that it is essential for second-order conditioning, an ethologically important form of higher-order associative learning. The Drosophila mushroom body comprises a series of dopaminergic compartments, each of which exhibits distinct memory dynamics. We find that a slow and stable memory compartment can serve as an effective 'teacher' by instructing other faster and transient memory compartments via a single key interneuron, which we identify by connectome analysis and neurotransmitter prediction. This excitatory interneuron acquires enhanced response to reward-predicting odor after first-order conditioning and, upon activation, evokes dopamine release in the 'student' compartments. These hierarchical connections between dopamine subsystems explain distinct properties of first- and second-order memory long known by behavioral psychologists.

Social cost of mining-related lead (Pb) pollution in Kabwe, Zambia, and potential remediation measures.

Lead (Pb) pollution has been one of the major environmental problems of worldwide significance. It is a latent factor for several fatal illnesses, whereas the exposure to lead in early childhood causes a lifetime IQ loss. The social cost is the concept to aggregate various adverse effects in a single monetary unit, which is useful in describing the pollution problem and provides foundation for the design of interventions. However, the assessment of the social cost is scarce for developing countries. In this study, we focus on the lead pollution problem of a former mining town, Kabwe, Zambia, where mining wastes abandoned near residential areas has caused a critical pollution problem. We first investigated the social cost of lead pollution that future generations born in 2025-2049 would incur in their lifetime. As the channels of the social cost, we considered the lost income from the IQ loss and the lost lives from lead-related mortality. The results showed that the social cost would amount to 224-593 million USD (discounted to the present value). Our results can be considered conservative, lower bound estimates because we focused only on well-identified effects of lead, but the social cost was still substantial. Then we examined several engineering remediation measures. The results showed that the social cost can be reduced (the benefits of remediations) more than the costs of implementing remediation measures. This study is the first to investigate the social cost of mining-related lead pollution problem in developing countries. Our interdisciplinary approach utilises the micro-level economic, health and pollution data and integrates the techniques in economics, toxicology and engineering.

Fourier-transform infrared study of the photoactivation process of Xenopus (6-4) photolyase.

Photolyases (PHRs) are blue light-activated DNA repair enzymes that maintain genetic integrity by reverting UV-induced photoproducts into normal bases. The flavin adenine dinucleotide (FAD) chromophore of PHRs has four different redox states: oxidized (FAD(ox)), anion radical (FAD(•-)), neutral radical (FADH(•)), and fully reduced (FADH(-)). We combined difference Fourier-transform infrared (FTIR) spectroscopy with UV-visible spectroscopy to study the detailed photoactivation process of Xenopus (6-4) PHR. Two photons produce the enzymatically active, fully reduced PHR from oxidized FAD: FAD(ox) is converted to semiquinone via light-induced one-electron and one-proton transfers and then to FADH(-) by light-induced one-electron transfer. We successfully trapped FAD(•-) at 200 K, where electron transfer occurs but proton transfer does not. UV-visible spectroscopy following 450 nm illumination of FAD(ox) at 277 K defined the FADH(•)/FADH(-) mixture and allowed calculation of difference FTIR spectra among the four redox states. The absence of a characteristic C=O stretching vibration indicated that the proton donor is not a protonated carboxylic acid. Structural changes in Trp and Tyr are suggested by UV-visible and FTIR analysis of FAD(•-) at 200 K. Spectral analysis of amide I vibrations revealed structural perturbation of the protein's ß-sheet during initial electron transfer (FAD(•-) formation), a transient increase in α-helicity during proton transfer (FADH(•) formation), and reversion to the initial amide I signal following subsequent electron transfer (FADH(-) formation). Consequently, in (6-4) PHR, unlike cryptochrome-DASH, formation of enzymatically active FADH(-) did not perturb α-helicity. Protein structural changes in the photoactivation of (6-4) PHR are discussed on the basis of these FTIR observations.

Dominance of the residential sector in Chinese black carbon emissions as identified from downwind atmospheric observations during the COVID-19 pandemic.

Emissions of black carbon (BC) particles from anthropogenic and natural sources contribute to climate change and human health impacts. Therefore, they need to be accurately quantified to develop an effective mitigation strategy. Although the spread of the emission flux estimates for China have recently narrowed under the constraints of atmospheric observations, consensus has not been reached regarding the dominant emission sector. Here, we quantified the contribution of the residential sector, as 64% (44-82%) in 2019, using the response of the observed atmospheric concentration in the outflowing air during Feb-Mar 2020, with the prevalence of the COVID-19 pandemic and restricted human activities over China. In detail, the BC emission fluxes, estimated after removing effects from meteorological variability, dropped only slightly (- 18%) during Feb-Mar 2020 from the levels in the previous year for selected air masses of Chinese origin, suggesting the contributions from the transport and industry sectors (36%) were smaller than the rest from the residential sector (64%). Carbon monoxide (CO) behaved differently, with larger emission reductions (- 35%) in the period Feb-Mar 2020, suggesting dominance of non-residential (i.e., transport and industry) sectors, which contributed 70% (48-100%) emission during 2019. The estimated BC/CO emission ratio for these sectors will help to further constrain bottom-up emission inventories. We comprehensively provide a clear scientific evidence supporting mitigation policies targeting reduction in residential BC emissions from China by demonstrating the economic feasibility using marginal abatement cost curves.

Exploration of natural red-shifted rhodopsins using a machine learning-based Bayesian experimental design.

Microbial rhodopsins are photoreceptive membrane proteins, which are used as molecular tools in optogenetics. Here, a machine learning (ML)-based experimental design method is introduced for screening rhodopsins that are likely to be red-shifted from representative rhodopsins in the same subfamily. Among 3,022 ion-pumping rhodopsins that were suggested by a protein BLAST search in several protein databases, the ML-based method selected 65 candidate rhodopsins. The wavelengths of 39 of them were able to be experimentally determined by expressing proteins with the Escherichia coli system, and 32 (82%, p = 7.025 × 10-5) actually showed red-shift gains. In addition, four showed red-shift gains >20 nm, and two were found to have desirable ion-transporting properties, indicating that they would be potentially useful in optogenetics. These findings suggest that data-driven ML-based approaches play effective roles in the experimental design of rhodopsin and other photobiological studies. (141/150 words).

Distinct subpopulations of mechanosensory chordotonal organ neurons elicit grooming of the fruit fly antennae.

Diverse mechanosensory neurons detect different mechanical forces that can impact animal behavior. Yet our understanding of the anatomical and physiological diversity of these neurons and the behaviors that they influence is limited. We previously discovered that grooming of the Drosophila melanogaster antennae is elicited by an antennal mechanosensory chordotonal organ, the Johnston's organ (JO) (Hampel et al., 2015). Here, we describe anatomically and physiologically distinct JO mechanosensory neuron subpopulations that each elicit antennal grooming. We show that the subpopulations project to different, discrete zones in the brain and differ in their responses to mechanical stimulation of the antennae. Although activation of each subpopulation elicits antennal grooming, distinct subpopulations also elicit the additional behaviors of wing flapping or backward locomotion. Our results provide a comprehensive description of the diversity of mechanosensory neurons in the JO, and reveal that distinct JO subpopulations can elicit both common and distinct behavioral responses.

Assessing the population-wide exposure to lead pollution in Kabwe, Zambia: an econometric estimation based on survey data.

This study quantitatively assessed the population-wide lead poisoning conditions in Kabwe, Zambia, a town with severe lead pollution. While existing data have reported concerning blood lead levels (BLLs) of residents in pollution hotspots, the data representing the entire population are lacking. Further, selection bias is a concern. Given the lack of compulsory testing schemes, BLLs have been observed from voluntary participants in blood sampling surveys, but such data can represent higher or lower BLLs than the population average because of factors simultaneously affecting participation and BLLs. To illustrate the lead poisoning conditions of the population, we expanded the focus of our surveys and then econometrically estimated the BLLs of individuals representing the population, including those not participating in blood sampling, using background geographic, demographic, and socioeconomic information. The estimated population mean BLL was 11.9 µg/dL (11.6-12.1, 95% CI), lower than existing data because of our wide focus and correction of selection bias. However, the scale of lead poisoning remained immense and 74.9% of residents had BLLs greater than 5 µg/dL, the standard reference level for lead poisoning. Our estimates provide a deeper understanding of the problem and a foundation for policy intervention designs.