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MamK, an actin-like protein conserved in magnetotactic bacteria, functions as a cytoskeletal element that positions the magnetosome, a bacterial geomagnetic sensor organelle. Specifically, MamK polymerizes into filaments associated with the magnetosome chain within each cell. The dynamics of these filaments are fundamental to magnetosome organelle positioning. However, the dynamic nature of the polymerized MamK filaments has not been characterized at the molecular level under physiological conditions. In this study, we used high-speed atomic force microscopy (AFM) to characterize the dynamic MamK polymerization process. MamK polymerized as double-helical filaments with a half-helical pitch distance of 41.3 ± 5.1 nm and a filament diameter of 6.3 ± 0.5 nm. The polymerizing MamK filaments elongated at average speeds of 12.4 ± 4.2 nm/min at the fast-growth ends (plus ends) and from − 4.4 to 8.0 nm/min at the slow-growth ends (minus ends) on the mica substrate in the solution containing 3 µM monomeric MamK. High-speed AFM demonstrated that MamK polymerized into dynamic double-helical filaments with polarity similar to that of eukaryotic actin filaments. Understanding the intrinsic dynamics of MamK, a well-conserved actin-like protein in magnetotactic bacteria, is key to elucidating the mechanism of magnetosome positioning in a bacterial cell.

The yeast prion protein Sup35, which contains intrinsically disordered regions, forms amyloid fibrils responsible for a prion phenotype [PSI⁺]. Using high-speed atomic force microscopy (HS-AFM), we directly visualized the prion determinant domain (Sup35NM) and the formation of its oligomers and fibrils at subsecond and submolecular resolutions. Monomers with freely moving tail-like regions initially appeared in the images, and subsequently oligomers with distinct sizes of ∼1.7 and 3 to 4 nm progressively accumulated. Nevertheless, these oligomers did not form fibrils, even after an incubation for 2 h in the presence of monomers. Fibrils appeared after much longer monomer incubation. The fibril elongation occurred smoothly without discrete steps, suggesting gradual conversions of the incorporated monomers into cross-β structures. The individual oligomers were separated from each other and also from the fibrils by respective, identical lengths on the mica surface, probably due to repulsion caused by the freely moving disordered regions. Based on these HS-AFM observations, we propose that the freely moving tails of the monomers are incorporated into the fibril ends, and then the structural conversions to cross-β structures gradually occur.

Magnetotactic bacteria are a unique group of bacteria that synthesize a magnetic organelle termed the magnetosome, which they use to assist with their magnetic navigation in a specific type of bacterial motility called magneto-aerotaxis. Cytoskeletal filaments consisting of the actin-like protein MamK are associated with the magnetosome chain. Previously, the function of MamK was thought to be in positioning magnetosome organelles; this was proposed based on observations via electron microscopy still images. Here, we conducted live-cell time-lapse fluorescence imaging analyses employing highly inclined and laminated optical sheet microscopy, and these methods enabled us to visualize detailed dynamic movement of magnetosomes in growing cells during the entire cell cycle with high-temporal resolution and a high signal/noise ratio. We found that the MamK cytoskeleton anchors magnetosomes through a mechanism that requires MamK-ATPase activity throughout the cell cycle to prevent simple diffusion of magnetosomes within the cell. We concluded that the static chain-like arrangement of the magnetosomes is required to precisely and consistently segregate the magnetosomes to daughter cells. Thus, the daughter cells inherit a functional magnetic sensor that mediates magneto-reception. IMPORTANCE Half a century ago, bacterial cells were considered a simple “bag of enzymes”; only recently have they been shown to comprise ordered complexes of macromolecular structures, such as bacterial organelles and cytoskeletons, similar to their eukaryotic counterparts. In eukaryotic cells, the positioning of organelles is regulated by cytoskeletal elements. However, the role of cytoskeletal elements in the positioning of bacterial organelles, such as magnetosomes, remains unclear. Magnetosomes are associated with cytoskeletal filaments that consist of the actin-like protein MamK. In this study, we focused on how the MamK cytoskeleton regulates the dynamic movement of magnetosome organelles in living magnetotactic bacterial cells. Here, we used fluorescence imaging to visualize the dynamics of magnetosomes throughout the cell cycle in living magnetotactic bacterial cells to understand how they use the actin-like cytoskeleton to maintain and to make functional their nano-sized magnetic organelles. Half a century ago, bacterial cells were considered a simple “bag of enzymes”; only recently have they been shown to comprise ordered complexes of macromolecular structures, such as bacterial organelles and cytoskeletons, similar to their eukaryotic counterparts. In eukaryotic cells, the positioning of organelles is regulated by cytoskeletal elements. However, the role of cytoskeletal elements in the positioning of bacterial organelles, such as magnetosomes, remains unclear. Magnetosomes are associated with cytoskeletal filaments that consist of the actin-like protein MamK. In this study, we focused on how the MamK cytoskeleton regulates the dynamic movement of magnetosome organelles in living magnetotactic bacterial cells. Here, we used fluorescence imaging to visualize the dynamics of magnetosomes throughout the cell cycle in living magnetotactic bacterial cells to understand how they use the actin-like cytoskeleton to maintain and to make functional their nano-sized magnetic organelles.

The detection of a silent interval or gap provides important insight into temporal processing by the auditory system. Previous research has uncovered a multitude of empirical findings leaving the mechanism of gap detection poorly understood and key issues unresolved. Here, we expand the findings by measuring psychometric functions for a number of conditions including both across-frequency and across-intensity gap detection as a first study of its kind. A model is presented which not only accounts for our findings in a quantitative manner, but also helps frame the body of work on auditory gap research. The model is based on the peripheral response and postulates that the identification of gap requires the detection of activity associated with silence.

Glass nanopipettes are widely used for various applications in nanosciences. In most of the applications, it is important to characterize their geometrical parameters, such as the aperture size and the inner cone angle at the tip region. For nanopipettes with sub-10 nm aperture and thin wall thickness, transmission electron microscopy (TEM) must be most instrumental in their precise geometrical measurement. However, this measurement has remained a challenge because heat generated by electron beam irradiation would largely deform sub-10-nm nanopipettes. Here we provide methods for preparing TEM specimens that do not cause deformation of such tiny nanopipettes.

The purpose of the present study is to examine the association between toddlers' sleep arrangements and their nighttime sleep duration and other sleep variables. For this investigation, we performed a study in which child activity and sleep levels were recorded using actigraphy. The parents of 1.5-year-old toddlers (n = 106) were asked to attach an actigraphy unit to their child’s waist with an adjustable elastic belt and complete a sleep diary for 7 consecutive days. Questionnaires were used to assess the sleep arrangements of the toddlers. There was a significant negative correlation between nap duration and nighttime sleep duration, suggesting that longer nap sleep induces shorter nighttime sleep duration. Among the sleep arrangements, such as nighttime breastfeeding or co-sleeping, only nighttime breastfeeding predicted shorter nighttime sleep duration. Our findings indicate that shorter naps induce a longer nighttime sleep in 1.5-year-old toddlers while nighttime breastfeeding decreases their nighttime sleep duration.

The demand for meta-analyses in basic biomedical research has been increasing because the phenotyping of genetically modified mice does not always produce consistent results. Melanin-concentrating hormone (MCH) has been reported to be involved in a variety of behaviors that include feeding, body-weight regulation, anxiety, sleep, and reward behavior. However, the reported behavioral and metabolic characteristics of MCH signaling-deficient mice, such as MCH-deficient mice and MCH receptor 1 (MCHR1)-deficient mice, are not consistent with each other. In the present study, we performed a meta-analysis of the published data related to MCH-deficient and MCHR1-deficient mice to obtain robust conclusions about the role of MCH signaling. Overall, the meta-analysis revealed that the deletion of MCH signaling enhanced wakefulness, locomotor activity, aggression, and male sexual behavior and that MCH signaling deficiency suppressed non-REM sleep, anxiety, responses to novelty, startle responses, and conditioned place preferences. In contrast to the acute orexigenic effect of MCH, MCH signaling deficiency significantly increased food intake. Overall, the meta-analysis also revealed that the deletion of MCH signaling suppressed the body weight, fat mass, and plasma leptin, while MCH signaling deficiency increased the body temperature, oxygen consumption, heart rate, and mean arterial pressure. The lean phenotype of the MCH signaling-deficient mice was also confirmed in separate meta-analyses that were specific to sex and background strain (i.e., C57BL/6 and 129Sv). MCH signaling deficiency caused a weak anxiolytic effect as assessed with the elevated plus maze and the open field test but also caused a weak anxiogenic effect as assessed with the emergence test. MCH signaling-deficient mice also exhibited increased plasma corticosterone under non-stressed conditions, which suggests enhanced activity of the hypothalamic-pituitary-adrenal axis. To the best of our knowledge, the present work is the first study to systematically compare the effects of MCH signaling on behavioral and metabolic phenotypes.

The present study developed a loop-mediated isothermal amplification (LAMP) assay that amplifies the fragments of O4 Salmonella enterica-specific gene rfbJ and evaluates the potential use in detection of Salmonella enterica serovar Typhimurium (ST). The detection limit of the LAMP assay was 103 CFU/ml, which was lower than that of the PCR assay with the same target gene (105 CFU/ml), confirmed by electrophoresis. The increased turbidity of the final products of LAMP was also observed with more than 103 CFU/ml. Furthermore, the LAMP assay took only 60 min for a reaction, while the PCR assay needed 80–90 min for a reaction and approximately 30 min for the subsequent electrophoresis to confirm the specific band. The positive reaction was only observed for 55 strains of 11 serovars of O4 group Salmonella enterica. The LAMP assay developed in the present study is considered to be an effective method for specific detection of the O4 group Salmonella enterica serovars, including ST.