Biology subjects

Hosokawa, T.

Publications and source records attributed to Hosokawa, T..

10 recordsLinked to original sources

bioRxiv2024

Cholesterol sulfate prevents maternal-fetal conflict by locally modulating immune reactivity

Although placental mammals are at high risk of maternal-fetal immune conflict, it is unclear how the semi-allogeneic fetus avoids rejection. Cholesterol sulfate (CS) is a bioactive metabolite that inhibits leukocyte migration and activation. This study investigated the roles and cells associated with CS in pregnant mice and humans. CS was sequentially produced by maternal-derived endometrial cells and fetal-derived placental trophoblasts before and after placentation. When mated with allogeneic males, CS-deficient mice showed increased fetal resorption rates under induced placental inflammation. This phenotype disappeared when the activity of the CS-producing enzyme was restored in the placenta. Placental CS levels were reduced in patients with "villitis of unknown etiology." Thus, we uncovered the spatiotemporal control of CS production and its relevance to local immunosuppression during pregnancy.

immunology↗

bioRxiv2024

The role of protein shape in multiphasic separation within condensates

Liquid-liquid phase separation (LLPS) of biological macromolecules leads to the formation of various membraneless organelles. LLPS can not only form homogenous condensates but also multilayered and multiphase condensates, which can mediate complex cellular functions. However, the factors that determine the topological features of multiphase condensates are not fully understood. Herein, we focused on Ca2+/calmodulin-dependent protein kinase II (CaMKII), a major postsynaptic protein that undergoes various forms of LLPS with other postsynaptic proteins, and present a minimalistic computational model that reproduces these forms of LLPS, including a form of two-phase condensates, phase-in-phase (PIP) organization. Analyses of this model revealed that the competitive binding of two types of client proteins is required for the PIP formation. The PIP only formed when CaMKII had high valency and a short linker length. Such CaMKII proteins exhibited a low surface tension, a modular structure, and slow diffusion. These properties are consistent with the functions required by CaMKII to store information at the synaptic level. Thus, the computational modeling reveals new structure-function relationships for CaMKII as a synaptic memory unit.

neuroscience↗

bioRxiv2024

Tryptophanase disruption underlies the evolution of insect-bacterium mutualism

Animal-microbe symbioses are omnipresent, where both partners often gain benefits as mutualists. How such mutualism has evolved between originally unrelated organisms is of interest. Here we report that, using an experimental symbiotic system between the stinkbug Plautia stali and the model bacterium Escherichia coli, disruption of a single bacterial gene tnaA encoding tryptophanase makes E. coli mutualistic to P. stali. Survey of natural bacterial mutualists across wild populations of P. stali and other stinkbug species uncovered that their Pantoea-allied symbionts consistently lack tnaA gene. Some Pantoea species like P. ananatis retain tnaA gene and cannot establish symbiosis with P. stali, but tnaA-disrupted P. ananatis partially restored the symbiotic capability. When a natural Pantoea mutualist of P. stali was transformed with a functional tna operon, its symbiotic capability reduced significantly. Our finding suggests that tryptophanase disruption may have facilitated the evolution of gut bacterial mutualists in insects.

evolutionary biology↗

bioRxiv2024

Defensive fungal symbiosis on insect hindlegs

Tympanal organs as "insect ears" have evolved repeatedly. Dinidorid stinkbugs were reported to possess a conspicuous tympanal organ on females hindlegs. Here we report an unexpected discovery that the stinkbugs "tympanal organ" is actually a novel symbiotic organ. The stinkbugs "tympanum" is not membranous but a porous cuticle, where each pore connects to glandular secretory cells. In reproductive females, the hindleg organ is covered with fungal hyphae growing out of the pores. Upon oviposition, the females skillfully transfer the fungi from the organ to the eggs. The eggs are quickly covered with hyphae and physically protected against wasp parasitism. The fungi are mostly benign Cordycipitaceae entomopathogens and show considerable diversity among insect individuals and populations, indicating environmental acquisition of specific fungal associates. These results uncover a novel external fungal symbiosis in which hosts elaborate morphological, physiological and behavioral specializations underpin the selective recruitment of benign entomopathogens for a defensive purpose.

microbiology↗

bioRxiv2023

Rapid Vacuolar Sorting of the Borate Transporter BOR1 Requires the Adaptor Protein Complex AP-4 in Arabidopsis

Plants maintain nutrient homeostasis by controlling the activities and abundance of nutrient transporters. In Arabidopsis thaliana, the borate (B) transporter BOR1 plays a role in the efficient translocation of B under low-B conditions. BOR1 undergoes polyubiquitination in the presence of sufficient B and is then transported to the vacuole via multivesicular bodies (MVBs) to prevent B accumulation in tissues at a toxic level. A previous study indicated that BOR1 physically interacts with subunits of adaptor protein complexes AP-3 and AP-4, both involved in vacuolar sorting pathways. In this study, we investigated the roles of AP-3 and AP-4 subunits in BOR1 trafficking in Arabidopsis. The lack of AP-3 subunits did not affect either vacuolar sorting or polar localization of BOR1-GFP, whereas the absence of AP-4 subunits resulted in a delay in high-B-induced vacuolar sorting without affecting polar localization. Super-resolution microscopy revealed a rapid sorting of BOR1-GFP into AP-4-positive spots in the trans-Golgi network (TGN) upon high-B supply. These results indicate that AP-4 is involved in sequestration of ubiquitinated BOR1 into a TGN-specific subdomain "vacuolar-trafficking zone," and is required for efficient sorting to MVB and vacuole. Our findings elucidate the rapid vacuolar sorting process facilitated by AP-4 in plant nutrient transporters. Subject areas(7) Membrane and transport

plant biology↗

bioRxiv2023

Contribution of default mode network to game and delayed-response task performance: power and connectivity analyses of theta oscillation in the monkey

Neuroimaging studies have demonstrated the presence of a default mode network (DMN) which shows greater activity during rest, and an executive network (EN) which is activated during cognitive tasks. DMN and EN are thought to have competing functions. However, recent studies reported that the two networks show coactivation during some cognitive tasks. To clarify how DMN works and how DMN interacts with EN for cognitive control, we recorded EEG activities in the medial prefrontal (anterior DMN: aDMN), posterior cingulate/precuneus (posterior DMN: pDMN), and lateral prefrontal (EN) areas in the monkey. As cognitive tasks, we employed a monkey-monkey competitive video game (GAME) and a delayed-response (DR) task. We focused on theta oscillation because of its importance in cognitive control. We also examined theta band connectivity among the three network areas using the Granger causality analysis. DMN and EN were found to work cooperatively in both tasks. In all the three network areas, we found GAME-task-related, but no DR-task-related, increase in theta power from the resting level, maybe because of the higher cognitive demand associated with the GAME task performance. The information flow conveyed by the theta oscillation was directed more to aDMN than from aDMN for both tasks. The GAME-task-related increase in theta power in aDMN is supposed to be supported by more information flow conveyed by the theta oscillation from EN and pDMN.

neuroscience↗

bioRxiv2022

Single mutation makes Escherichia coli an insect mutualist

We report an experimental system in which Escherichia coli evolves into an insect mutualist. When the essential gut symbiont of the stinkbug Plautia stali was replaced by E. coli, a few survivor insects exhibited specific localization and vertical transmission of E. coli. Through trans-generational maintenance with P. stali, several hyper-mutating E. coli lines independently evolved hosts high adult emergence and improved body color. Such "mutualistic" E. coli lines exhibited independent mutations disrupting the carbon catabolite repression (CCR) global transcriptional regulator. Each of the mutations reproduced the mutualistic phenotypes when introduced into wild-type E. coli, confirming that the single CCR mutations instantly make E. coli an insect mutualist. Our discovery uncovers that evolution of elaborate mutualism can proceed more easily and rapidly than conventionally envisaged.

evolutionary biology↗

bioRxiv2020

CaMKII activation triggers persistent formation and segregation of postsynaptic liquid phase

Transient information input to brain leads to persistent changes in synaptic circuit, thereby forming memory engrams. Synapse undergoes coordinated functional and structural changes during this process but how such changes are achieved by its component molecules still largely remain enigmatic. We found that activated CaMKII, the central player of synaptic plasticity, undergoes liquid-liquid phase separation (LLPS) with NMDAR subunit GluN2B. Due to CaMKII autophosphorylation, the condensate stably persists even after Ca2+ is removed. The selective binding of activated CaMKII with GluN2B co-segregates AMPAR/neuroligin (NLGN) into a phase-in-phase assembly. Because postsynaptic NLGN clusters presynaptic neurexin and other active zone proteins thereby increasing the release probability of synaptic vesicles, this ensures efficient synaptic transmission. In this way, Ca2+-induced and persistent formation of LLPS by CaMKII serves as molecular basis of memory by functioning as an activity-dependent crosslinker for postsynaptic proteins and segregating trans-synaptic nanocolumns.

neuroscience↗

bioRxiv2019

Molecular determinants of Arc oligomerization and formation of virus-like capsids

Expression of activity-regulated cytoskeleton-associated protein (Arc) is critical for long-term synaptic plasticity, memory formation, and cognitive flexibility. The ability of Arc to self-associate and form virus-like capsid structures implies functionally distinct oligomeric states. However, the molecular mechanism of Arc oligomerization is unknown. Here, we identified a 28-amino-acid region necessary and sufficient for Arc oligomerization. This oligomerization region is located within the second coil of a predicted anti-parallel coiled-coil in the N-terminal domain (NTD). Using alanine scanning mutagenesis, we found a 7-amino-acid motif critical for oligomerization and Arc-mediated transferrin endocytosis in HEK cells. Intermolecular fluorescence lifetime imaging in hippocampal neurons confirmed self-association mediated by the motif. To quantify oligomeric size, we performed a single-molecule photobleaching analysis of purified Arc wild-type and mutant. This analysis revealed a critical role for the NTD motif in the formation of higher-order Arc oligomers (30-170 molecules). Moreover, assembly of higher-order wild-type Arc oligomers was significantly enhanced by addition of GFP RNA. Purified wild-type Arc formed virus-like capsids, as visualized by negative-stain EM, and was estimated by light scattering analysis to contain 40-55 Arc units. In contrast, mutant Arc formed a homogenous dimer population as demonstrated by single-molecule TIRF imaging, size-exclusion chromatography with multi-angle light scattering analysis, small-angle X-ray scattering analysis, and single-particle 3D EM reconstruction. Thus, the dimer appears to be the basic building block for assembly. Herein, we show that the NTD motif is essential for higher-order Arc oligomerization, assembly of virus-like capsid particles, and facilitation of oligomerization by exogenous RNA. SIGNIFICANCEArc protein is rapidly expressed in neurons in response to synaptic activity and plays critical roles in synaptic plasticity, postnatal cortical developmental, and memory. Arc has diverse molecular functions, which may be related to distinct oligomeric states of the protein. Arc has homology to retroviral Gag protein and self-assembles into retrovirus-like capsid structures that are capable of intercellular transfer of RNA. Here, we identified a motif in the N-terminal coiled-coil domain of mammalian Arc that mediates higher-order oligomerization and formation of virus-like capsids. The basic building block is the Arc dimer and exogenous RNA facilitates further assembly. The identified molecular determinants of Arc oligomerization will help to elucidate the functional modalities of Arc in the mammalian brain.

biochemistry↗

bioRxiv2018

Structure of monomeric full-length ARC sheds light on molecular flexibility, protein interactions, and functional modalities

The activity-regulated cytoskeleton-associated protein (ARC) is critical for long-term synaptic plasticity and memory formation. Acting as a protein interaction hub, ARC regulates diverse signalling events in postsynaptic neurons. A protein interaction site is present in the ARC C-terminal domain (CTD), a bilobar structure homologous to the retroviral Gag capsid domain. However, knowledge of the 3-dimensional structure of full-length ARC is required to elucidate its molecular function. We purified recombinant monomeric full-length ARC and analyzed its structure using small-angle X-ray scattering and synchrotron radiation circular dichroism spectroscopy. In solution, monomeric ARC has a compact, closed structure, in which the oppositely charged N-terminal domain (NTD) and CTD are juxtaposed, and the flexible linker between them is not extended. The modelled structure of ARC is supported by intramolecular live-cell FRET imaging in rat hippocampal slices. Peptides from several postsynaptic proteins, including stargazin, bind to the N-lobe, but not to the C-lobe, of the bilobar CTD. This interaction does not induce large-scale conformational changes in the CTD or flanking unfolded regions. The ARC NTD contains long helices, predicted to form an anti-parallel coiled coil; binding of ARC to phospholipid membranes requires the NTD. Our data support a role for the ARC NTD in oligomerization as well as lipid membrane binding. These findings have important implications for the structural organization of ARC in distinct functional modalities, such as postsynaptic signal transduction and virus-like capsid formation.

biophysics↗