Geometric trade-off between contractile force and viscous drag determines the actomyosin-based motility of a cell-sized droplet

動きまわる人工細胞、その鍵は摩擦にあり --細胞が狭い空間を利用して運動する仕組みを解明--. 京都大学プレスリリース. 2022-07-21.Cell migration in confined environments is fundamental for diverse biological processes from cancer invasion to leukocyte trafficking. The cell body is propelled by the contractile force of actomyosin networks transmitted from the cell membrane to the external substrates. However, physical determinants of actomyosin-based migration capacity in confined environments are not fully understood. Here, we develop an in vitro migratory cell model, where cytoplasmic actomyosin networks are encapsulated into droplets surrounded by a lipid monolayer membrane. We find that the droplet can move when the actomyosin networks are bound to the membrane, in which the physical interaction between the contracting actomyosin networks and the membrane generates a propulsive force. The droplet moves faster when it has a larger contact area with the substrates, while narrower confinement reduces the migration speed. By combining experimental observations and active gel theory, we propose a mechanism where the balance between sliding friction force, which is a reaction force of the contractile force, and viscous drag determines the migration speed, providing a physical basis of actomyosin-based motility in confined environments

A Study on Equivalent Circuit Modeling of Wiring Inductance in SiC Power Module for Predicting Conducted EMI of Power Converter

C. Kyotani, I. Takaaki, T. Funaki, T. Miyazaki, Y. Okawauchi and K. Nakahara, "A Study on Equivalent Circuit Modeling of Wiring Inductance in SiC Power Module for Predicting Conducted EMI of Power Converter," 2020 IEEE 11th International Symposium on Power Electronics for Distributed Generation Systems (PEDG), Dubrovnik, Croatia, 2020, pp. 435-440, doi: 10.1109/PEDG48541.2020.9244460

Operando analysis of graphite intercalation compounds with fluoride-containing polyatomic anions in aqueous solutions

The formation of graphite intercalation compounds (GICs) in aqueous solutions has attracted much attention, but reversibility in the formation/deformation of GICs is a challenging issue to construct highly safe rechargeable batteries. In this study, we used an operando analysis (X-ray diffraction and Raman spectroscopy) to discuss the feasibility of using fluoride-containing polyatomic anions in the formation of GICs in aqueous highly concentrated solutions. We found that the intercalation of anions containing a C₂F₅ moiety (such as [N(SO₂CF₃)(SO₂CF₂CF₃)]⁻ or [N(SO₂CF₂CF₃)₂]⁻) does not occur in the bulk of graphite, but only in the surface region. In addition, anions containing a CF₃ moiety show different behaviors: SO₃CF₃⁻ shows greater reversibility and larger stage-number than N(SO₂CF₃)₂⁻ in the formation of GICs. These results provide design guidelines for the reversible intercalation and de-intercalation of anions and their application as a cathode material in aqueous rechargeable batteries

Peptide barcoding for one-pot evaluation of sequence–function relationships of nanobodies

遊離型抗体の構造活性相関解析を迅速に評価可能とする新手法を開発. 京都大学プレスリリース. 2021-11-08.Optimisation of protein binders relies on laborious screening processes. Investigation of sequence–function relationships of protein binders is particularly slow, since mutants are purified and evaluated individually. Here we developed peptide barcoding, a high-throughput approach for accurate investigation of sequence–function relationships of hundreds of protein binders at once. Our approach is based on combining the generation of a mutagenised nanobody library fused with unique peptide barcodes, the formation of nanobody–antigen complexes at different ratios, their fine fractionation by size-exclusion chromatography and quantification of peptide barcodes by targeted proteomics. Applying peptide barcoding to an anti-GFP nanobody as a model, we successfully identified residues important for the binding affinity of anti-GFP nanobody at once. Peptide barcoding discriminated subtle changes in KD at the order of nM to sub-nM. Therefore, peptide barcoding is a powerful tool for engineering protein binders, enabling reliable one-pot evaluation of sequence–function relationships

microRNA-875-5p plays critical role for mesenchymal condensation in epithelial-mesenchymal interaction during tooth development

Epithelial-mesenchymal interaction has critical roles for organ development including teeth, during which epithelial thickening and mesenchymal condensation are initiated by precise regulation of the signaling pathway. In teeth, neural crest-derived mesenchymal cells expressed PDGF receptors migrate and become condensed toward invaginated epithelium. To identify the molecular mechanism of this interaction, we explored the specific transcriptional start sites (TSSs) of tooth organs using cap analysis of gene expression (CAGE). We identified a tooth specific TSS detected in the chromosome 15qD1 region, which codes microRNA-875 (mir875). MiR875-5p is specifically expressed in dental mesenchyme during the early stage of tooth development. Furthermore, PRRX1/2 binds to the mir875 promoter region and enhances the expression of mir875. To assess the role of miR875-5p in dental mesenchyme, we transfected mimic miR875-5p into mouse dental pulp (mDP) cells, which showed that cell migration toward dental epithelial cells was significantly induced by miR875-5p via the PDGF signaling pathway. Those results also demonstrated that miR875-5p induces cell migration by inhibiting PTEN and STAT1, which are regulated by miR875-5p as part of post-transcriptional regulation. Together, our findings indicate that tooth specific miR875-5p has important roles in cell condensation of mesenchymal cells around invaginated dental epithelium and induction of epithelial-mesenchymal interaction

Predicting effects of climate change on productivity and persistence of forest trees

Global climate change increases uncertainty in sustained functioning of forest ecosystems. Forest canopies are a key link between terrestrial ecosystems, the atmosphere, and climate. Here, we introduce research presented at the 66th meeting of the Ecological Society of Japan in the symposium “Structure and function of forest canopies under climate change.” Old-growth forest carbon stores are the largest and may be the most vulnerable to climate change as the balance between sequestration and emission could easily be tipped. Detailed structural analysis of individual large, old trees shows they are allocating wood to the trunk and crown in patterns that cannot be deduced from ground, thus can be used to more accurately quantify total forest carbon and sequestration. Slowly migrating species sensitive to novel climatic conditions will have to acclimate at the individual level. Accounting for physiological responses of trees to climate change will improve predictions of future species distributions and subsequent functioning of forest ecosystems. Field experiments manipulating temperature and precipitation show how trees compensate physiologically to mitigate for higher temperatures and drought. However, it is difficult to measure acclimation responses over long timeframes. Intraindividual trait variation is proposed as an indicator of acclimation potential of trees to future conditions and suggests that acclimation potential may vary among regional populations within a species. Integrating whole-tree structural data with physiological data offers a promising avenue for understanding how trees will respond to climatic shifts

Design and lyophilization of lipid nanoparticles for mRNA vaccine and its robust immune response in mice and nonhuman primates

mRNA and lipid nanoparticles have emerged as powerful systems for the preparation of vaccines against severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection. The emergence of novel variants or the necessity of cold chain logistics for approved mRNA vaccines undermines the investigation of next-generation systems that could preserve both potency and stability. However, the correlation between lipid nanoparticle composition and activity is not fully explored. Here, we screened a panel of ionizable lipids in vivo and identified lead lipid nanoparticles with a branched-tail lipid structure. Buffer optimization allowed the determination of lyophilization conditions, where lipid nanoparticle-encapsulated mRNA encoding SARS-CoV-2 spike protein could induce robust immunogenicity in mice after 1 month of storage at 5°C and 25°C. Intramuscularly injected lipid nanoparticles distributed in conventional dendritic cells in mouse lymph nodes induced balanced T helper (Th) 1/Th2 responses against SARS-CoV-2 spike protein. In nonhuman primates, two doses of 10 or 100 μg of mRNA induced higher spike-specific binding geometric mean titers than those from a panel of SARS-CoV-2-convalescent human sera. Immunized sera broadly inhibited the viral entry receptor angiotensin-converting enzyme 2 (ACE2) from binding to the spike protein in all six strains tested, including variants of concern. These results could provide useful information for designing next-generation mRNA vaccines