A case of drug-induced organizing pneumonia caused by amikacin liposome inhalation suspension

Inhaled liposomal antimicrobials are known to cause hypersensitivity pneumonitis. Amikacin liposome inhalation suspension (ALIS) is a promising novel antimicrobial agent against refractory Mycobacterium avium complex infections. The frequency of drug-induced lung injury caused by ALIS is relatively high. To date, no reports of ALIS-induced organizing pneumonia diagnosed by bronchoscopy are available. We report a case of a 74-year-old female patient presenting with non-tuberculous mycobacterial pulmonary disease (NTM-PD). She was treated with ALIS for refractory NTM-PD. Fifty-nine days after starting ALIS, the patient developed a cough, and her chest radiographs indicated deterioration. She was diagnosed with organizing pneumonia based on pathological findings of the lung tissues obtained by bronchoscopy. After switching from ALIS to amikacin infusion, her organizing pneumonia improved. It is difficult to distinguish between organizing pneumonia and an exacerbation of NTM-PD based on chest radiography alone. Therefore, it is essential to perform an active bronchoscopy for diagnosis.

Pulmonary Langerhans Cell Histiocytosis That Progressed from a Single-system to a Multisystem Form despite Smoking Cessation

A 36-year-old Japanese man presented with cavities and nodular shadows in the lower lobes of his lungs and osteolytic lesions in the thoracic spine. He was diagnosed with multisystem Langerhans cell histiocytosis (LCH). Three years earlier, he had been noted to have small cavities and granular lesions noted in the upper lobes of his lungs, which later improved with smoking cessation. It was likely that his single-system pulmonary LCH (PLCH) progressed to multisystem LCH despite smoking cessation. Relapse or progression may occur in cases where PLCH lesions improve after smoking cessation. Thus, close follow-up is vital.

Light-sheet microscopy reveals dorsoventral asymmetric membrane dynamics of Amoeba proteus during pressure-driven locomotion

Amoebae are found all around the world and play an essential role in the carbon cycle in the environment. Therefore, the behavior of amoebae is a crucial factor when considering the global environment. Amoebae change their distribution through amoeboid locomotion, which are classified into several modes. In the pressure-driven mode, intracellular hydrostatic pressure generated by the contraction of cellular cortex actomyosin causes the pseudopod to extend. During amoeboid locomotion, the cellular surface exhibits dynamic deformation. Therefore, to understand the mechanism of amoeboid locomotion, it is important to characterize cellular membrane dynamics. Here, to clarify membrane dynamics during pressure-driven amoeboid locomotion, we developed a polkadot membrane staining method and performed light-sheet microscopy in Amoeba proteus, which exhibits typical pressure-driven amoeboid locomotion. It was observed that the whole cell membrane moved in the direction of movement, and the dorsal cell membrane in the posterior part of the cell moved more slowly than the other membrane. In addition, membrane complexity varied depending on the focused characteristic size of the membrane structure, and in general, the dorsal side was more complex than the ventral side. In summary, the membrane dynamics of Amoeba proteus during pressure-driven locomotion are asymmetric between the dorsal and ventral sides. This article has an associated interview with the co-first authors of the paper.

A Primer on Deep Learning-Based Cellular Image Classification of Changes in the Spatial Distribution of the Golgi Apparatus After Experimental Manipulation

The visual classification of cell images according to differences in the spatial patterns of subcellular structure is an important methodology in cell and developmental biology. Experimental perturbation of cell function can induce changes in the spatial distribution of organelles and their associated markers or labels. Here, we demonstrate how to achieve accurate, unbiased, high-throughput image classification using an artificial intelligence (AI) algorithm. We show that a convolutional neural network (CNN) algorithm can classify distinct patterns of Golgi images after drug or siRNA treatments, and we review our methods from cell preparation to image acquisition and CNN analysis.

Preprint Highlight: Real-time denoising of fluorescence time-lapse imaging enables high-sensitivity observations of biological dynamics beyond the shot-noise limit

Denoising in fluorescence imaging is a key technology to boost sensitivity and detect low signals buried in noise. While previous deep learning-based algorithms have been demonstrated to improve denoising quality, their application has been limited by the time-consuming processing step. This study demonstrates a much faster deep learning-based denoising algorithm, DeepCAD-RT, that enables real-time processing of fluorescence live cell images and can be incorporated into the data acquisition pipeline of a microscopy system. In addition to its obvious advantage in improving workflow efficiency, DeepCAD-RT could also have an impact on robotics technologies, such as automatic microinjection and cell picking, that require highly sensitive and real-time recognition of cells under a microscope.

Preprint Highlight: Multiplexed bioluminescence microscopy via phasor analysis

Luciferase‐based bioluminescence imaging requires no excitation light and thus can be advantageous over fluorescence imaging, but multicolor imaging has been a challenge due to the difficulties of spectral and substrate unmixing. To achieve effective multiplexing of bioluminescence imaging, this study applies phasor analysis that can cluster profiles, in the phasor space, of acquired light intensity according to specific bioluminescence probes. The authors demonstrate that bioluminescence phasor imaging can distinguish heterogeneous cell populations expressing up to six unique reporters. They also resolve two distinct reporters localized to the nucleus and plasma membrane within a single cell. The workflow and optical setup are simple and easily accessible to most cell and developmental biologists, which enables multicolor live‐cell imaging without concerns of photodamage.

Centriole and PCM cooperatively recruit CEP192 to spindle poles to promote bipolar spindle assembly

The pericentriolar material (PCM) that accumulates around the centriole expands during mitosis and nucleates microtubules. Here, we show the cooperative roles of the centriole and PCM scaffold proteins, pericentrin and CDK5RAP2, in the recruitment of CEP192 to spindle poles during mitosis. Systematic depletion of PCM proteins revealed that CEP192, but not pericentrin and/or CDK5RAP2, was crucial for bipolar spindle assembly in HeLa, RPE1, and A549 cells with centrioles. Upon double depletion of pericentrin and CDK5RAP2, CEP192 that remained at centriole walls was sufficient for bipolar spindle formation. In contrast, through centriole removal, we found that pericentrin and CDK5RAP2 recruited CEP192 at the acentriolar spindle pole and facilitated bipolar spindle formation in mitotic cells with one centrosome. Furthermore, the perturbation of PLK1, a critical kinase for PCM assembly, efficiently suppressed bipolar spindle formation in mitotic cells with one centrosome. Overall, these data suggest that the centriole and PCM scaffold proteins cooperatively recruit CEP192 to spindle poles and facilitate bipolar spindle formation.

Structure Optimization of Gatastatin for the Development of γ-Tubulin-Specific Inhibitor

Gatastatin (O ⁷-benzyl glaziovianin A) is a γ-tubulin-specific inhibitor that is used to investigate γ-tubulin function in cells. We have previously reported that the unsubstituted phenyl ring of the O ⁷-benzyl group in gatastatin is important for γ-tubulin inhibition. To obtain further structural information regarding γ-tubulin inhibition, we synthesized several gatastatin derivatives containing a fixed O ⁷-benzyl moiety. Modifications of the B-ring resulted in drastic decrease in cytotoxicity, abnormal spindle formation activity, and inhibition of microtubule (MT) nucleation. In contrast, various O ⁶-alkylated gatastatin derivatives showed potent cytotoxicity, induced abnormal spindle formation, and inhibited MT nucleation. We had previously reported that O ⁶-benzyl glaziovianin A is a potent α/β-tubulin inhibitor; thus, these new results suggest that the O ⁶-position restricts affinity for α/β- and γ-tubulin. Considering that an O ⁷-benzyl group increases specificity for γ-tubulin, more potent and specific γ-tubulin inhibitors can be generated through O ⁶-modifications of gatastatin.

Robust classification of cell cycle phase and biological feature extraction by image-based deep learning

Across the cell cycle, the subcellular organization undergoes major spatiotemporal changes that could in principle contain biological features that could potentially represent cell cycle phase. We applied convolutional neural network-based classifiers to extract such putative features from the fluorescence microscope images of cells stained for the nucleus, the Golgi apparatus, and the microtubule cytoskeleton. We demonstrate that cell images can be robustly classified according to G1/S and G2 cell cycle phases without the need for specific cell cycle markers. Grad-CAM analysis of the classification models enabled us to extract several pairs of quantitative parameters of specific subcellular features as good classifiers for the cell cycle phase. These results collectively demonstrate that machine learning-based image processing is useful to extract biological features underlying cellular phenomena of interest in an unbiased and data-driven manner.

NuMA assemblies organize microtubule asters to establish spindle bipolarity in acentrosomal human cells

In most animal cells, mitotic spindle formation is mediated by coordination of centrosomal and acentrosomal pathways. At the onset of mitosis, centrosomes promote spindle bipolarization. However, the mechanism through which the acentrosomal pathways facilitate the establishment of spindle bipolarity in early mitosis is not completely understood. In this study, we show the critical roles of nuclear mitotic apparatus protein (NuMA) in the generation of spindle bipolarity in acentrosomal human cells. In acentrosomal human cells, we found that small microtubule asters containing NuMA formed at the time of nuclear envelope breakdown. In addition, these asters were assembled by dynein and the clustering activity of NuMA. Subsequently, NuMA organized the radial array of microtubules, which incorporates Eg5, and thus facilitated spindle bipolarization. Importantly, in cells with centrosomes, we also found that NuMA promoted the initial step of spindle bipolarization in early mitosis. Overall, these data suggest that canonical centrosomal and NuMA-mediated acentrosomal pathways redundantly promote spindle bipolarity in human cells.

NPHP proteins are binding partners of nucleoporins at the base of the primary cilium

Cilia are microtubule-based organelles that protrude from the surface of eukaryotic cells to generate motility and to sense and respond to environmental cues. In order to carry out these functions, the complement of proteins in the cilium must be specific for the organelle. Regulation of protein entry into primary cilia has been shown to utilize mechanisms and components of nuclear gating, including nucleoporins of the nuclear pore complex (NPC). We show that nucleoporins also localize to the base of motile cilia on the surface of trachea epithelial cells. How nucleoporins are anchored at the cilium base has been unclear as transmembrane nucleoporins, which anchor nucleoporins at the nuclear envelope, have not been found to localize at the cilium. Here we use the directed yeast two-hybrid assay to identify direct interactions between nucleoporins and nephronophthisis proteins (NPHPs) which localize to the cilium base and contribute to cilium assembly and identity. We validate NPHP-nucleoporin interactions in mammalian cells using the knocksideways assay and demonstrate that the interactions occur at the base of the primary cilium using bimolecular fluorescence complementation. We propose that NPHP proteins anchor nucleoporins at the base of primary cilia to regulate protein entry into the organelle.

Feedback loops in the Plk4-STIL-HsSAS6 network coordinate site selection for procentriole formation

Centrioles are duplicated once in every cell cycle, ensuring the bipolarity of the mitotic spindle. How the core components cooperate to achieve high fidelity in centriole duplication remains poorly understood. By live-cell imaging of endogenously tagged proteins in human cells throughout the entire cell cycle, we quantitatively tracked the dynamics of the critical duplication factors: Plk4, STIL and HsSAS6. Centriolar Plk4 peaks and then starts decreasing during the late G1 phase, which coincides with the accumulation of STIL at centrioles. Shortly thereafter, the HsSAS6 level increases steeply at the procentriole assembly site. We also show that both STIL and HsSAS6 are necessary for attenuating Plk4 levels. Furthermore, our mathematical modeling and simulation suggest that the STIL-HsSAS6 complex in the cartwheel has a negative feedback effect on centriolar Plk4. Combined, these findings illustrate how the dynamic behavior of and interactions between critical duplication factors coordinate the centriole-duplication process.This article has an associated First Person interview with the first author of the paper.

A theory of centriole duplication based on self-organized spatial pattern formation

Super-resolution imaging combined with quantitative image analyses reveals dynamic spatial pattern formation of centriolar Plk4, a master regulator of centriole duplication. The self-organization properties of Plk4 exclusively provide the single site for centriole formation around the preexisting centriole.

In each cell cycle, centrioles are duplicated to produce a single copy of each preexisting centriole. At the onset of centriole duplication, the master regulator Polo-like kinase 4 (Plk4) undergoes a dynamic change in its spatial pattern around the preexisting centriole, forming a single duplication site. However, the significance and mechanisms of this pattern transition remain unknown. Using super-resolution imaging, we found that centriolar Plk4 exhibits periodic discrete patterns resembling pearl necklaces, frequently with single prominent foci. Mathematical modeling and simulations incorporating the self-organization properties of Plk4 successfully generated the experimentally observed patterns. We therefore propose that the self-patterning of Plk4 is crucial for the regulation of centriole duplication. These results, defining the mechanisms of self-organized regulation, provide a fundamental principle for understanding centriole duplication.

The Cep57-pericentrin module organizes PCM expansion and centriole engagement

Centriole duplication occurs once per cell cycle to ensure robust formation of bipolar spindles and chromosome segregation. Each newly-formed daughter centriole remains connected to its mother centriole until late mitosis. The disengagement of the centriole pair is required for centriole duplication. However, the mechanisms underlying centriole engagement remain poorly understood. Here, we show that Cep57 is required for pericentriolar material (PCM) organization that regulates centriole engagement. Depletion of Cep57 causes PCM disorganization and precocious centriole disengagement during mitosis. The disengaged daughter centrioles acquire ectopic microtubule-organizing-center activity, which results in chromosome mis-segregation. Similar defects are observed in mosaic variegated aneuploidy syndrome patient cells with cep57 mutations. We also find that Cep57 binds to the well-conserved PACT domain of pericentrin. Microcephaly osteodysplastic primordial dwarfism disease pericentrin mutations impair the Cep57-pericentrin interaction and lead to PCM disorganization. Together, our work demonstrates that Cep57 provides a critical interface between the centriole core and PCM.

Centriole disengagement occurs towards mitotic exit and involves cleavage of pericentrin, a component of the pericentriolar material. Here the authors show that depletion of the centrosomal protein Cep57 leads to precocious centriole disengagement, and that Cep57 binds pericentrin.

Axonemal Lumen Dominates Cytosolic Protein Diffusion inside the Primary Cilium

Transport of membrane and cytosolic proteins in primary cilia is thought to depend on intraflagellar transport (IFT) and diffusion. However, the relative contribution and spatial routes of each transport mechanism are largely unknown. Although challenging to decipher, the details of these routes are essential for our understanding of protein transport in primary cilia, a critically affected process in many genetic diseases. By using a high-speed virtual 3D super-resolution microscopy, we have mapped the 3D spatial locations of transport routes for various cytosolic proteins in the 250-nm-wide shaft of live primary cilia with a spatiotemporal resolution of 2 ms and <16 nm. Our data reveal two spatially distinguishable transport routes for cytosolic proteins: an IFT-dependent path along the axoneme, and a passive-diffusion route in the axonemal lumen that escaped previous studies. While all cytosolic proteins tested primarily utilize the IFT path in the anterograde direction, differences are observed in the retrograde direction where IFT20 only utilizes IFT, and approximately half of KIF17 and one third of α–tubulin utilizes diffusion besides IFT.

Protein Interaction Analysis Provides a Map of the Spatial and Temporal Organization of the Ciliary Gating Zone

The motility and signaling functions of the primary cilium require a unique protein and lipid composition that is determined by gating mechanisms localized at the base of the cilium. Several protein complexes localize to the gating zone and may regulate ciliary protein composition; however, the mechanisms of ciliary gating and the dynamics of the gating components are largely unknown. Here, we used the BiFC (bimolecular fluorescence complementation) assay and report for the first time on the protein-protein interactions that occur between ciliary gating components and transiting cargoes during ciliary entry. We find that the nucleoporin Nup62 and the C termini of the nephronophthisis (NPHP) proteins NPHP4 and NPHP5 interact with the axoneme-associated kinesin-2 motor KIF17 and thus spatially map to the inner region of the ciliary gating zone. Nup62 and NPHP4 exhibit rapid turnover at the transition zone and thus define dynamic components of the gate. We find that B9D1, AHI1, and the N termini of NPHP4 and NPHP5 interact with the transmembrane protein SSTR3 and thus spatially map to the outer region of the ciliary gating zone. B9D1, AHI1, and NPHP5 exhibit little to no turnover at the transition zone and thus define components of a stable gating structure. These data provide the first comprehensive map of the molecular orientations of gating zone components along the inner-to-outer axis of the ciliary gating zone. These results advance our understanding of the functional roles of gating zone components in regulating ciliary protein composition.

Simulation of intra-ciliary diffusion suggests a novel role of primary cilia as a cell-signaling enhancer

Besides the role to generate a fluid flow in the surrounding medium, eukaryotic cilia have a crucial function in sensing external signals such as chemical or mechanical stimuli. A large body of work has shown that cilia are frequently found in various types of sensory cells and are closely related to many regulatory mechanisms in differentiation and development. However, we do not yet have a definitive answer to the fundamental question, "why cilia?" It has been a long-standing mystery why cells use cilia for sensing external signals. To shed light on this, we sought to describe the kinetics of signaling with theoretical approaches. Based on the results, here we propose a new role of cilia as a cell-signaling enhancer. The enhancing effect comes from restricted volume for the free intra-ciliary diffusion of molecules due to the cylindrical shape of cilia, which can facilitate quick accumulation of intracellular signaling molecules. Our simulations demonstrate that both the rate and amplitude of response in signal transduction depend on where the membrane receptors or channels are located along the ciliary shaft. In addition, the calculated transfer function of cilia regarded as a transmitter of external signals also suggests the properties of cilia as a signal enhancer. Since such unique composition of receptors and channels in cilia is found in various types of eukaryotic cells, signal enhancing is presumably one of the most essential and conserved roles of cilia.

Gated entry into the ciliary compartment

Cilia and flagella play important roles in cell motility and cell signaling. These functions require that the cilium establishes and maintains a unique lipid and protein composition. Recent work indicates that a specialized region at the base of the cilium, the transition zone, serves as both a barrier to entry and a gate for passage of select components. For at least some cytosolic proteins, the barrier and gate functions are provided by a ciliary pore complex (CPC) that shares molecular and mechanistic properties with nuclear gating. Specifically, nucleoporins of the CPC limit the diffusional entry of cytosolic proteins in a size-dependent manner and enable the active transport of large molecules and complexes via targeting signals, importins, and the small G protein Ran. For membrane proteins, the septin protein SEPT2 is part of the barrier to entry whereas the gating function is carried out and/or regulated by proteins associated with ciliary diseases (ciliopathies) such as nephronophthisis, Meckel–Gruber syndrome and Joubert syndrome. Here, we discuss the evidence behind these models of ciliary gating as well as the similarities to and differences from nuclear gating.

Methods for Studying Ciliary Import Mechanisms

Cilia and flagella are microtubule-based organelles that play important roles in human health by contributing to cellular motility as well as sensing and responding to environmental cues. Defects in cilia formation and function cause a broad class of human genetic diseases called ciliopathies. To carry out their specialized functions, cilia contain a unique complement of proteins that must be imported into the ciliary compartment. In this chapter, we describe methods to measure the permeability barrier of the ciliary gate by microinjection of fluorescent proteins and dextrans of different sizes into ciliated cells. We also describe a fluorescence recovery after photobleaching (FRAP) assay to measure the entry of ciliary proteins into the ciliary compartment. These assays can be used to determine the molecular mechanisms that regulate the formation and function of cilia in mammalian cells.

An assay for clogging the ciliary pore complex distinguishes mechanisms of cytosolic and membrane protein entry

As a cellular organelle, the cilium contains a unique protein composition. Entry of both membrane and cytosolic components is tightly regulated by gating mechanisms at the cilium base; however, the mechanistic details of ciliary gating are largely unknown. We previously proposed that entry of cytosolic components is regulated by mechanisms similar to those of nuclear transport and is dependent on nucleoporins (NUPs), which comprise a ciliary pore complex (CPC). To investigate ciliary gating mechanisms, we developed a system to clog the pore by inhibiting NUP function via forced dimerization. We targeted NUP62, a component of the central channel of the nuclear pore complex (NPC), for forced dimerization by tagging it with the homodimerizing Fv domain. As proof of principle, we show that forced dimerization of NUP62-Fv attenuated (1) active transport of BSA into the nuclear compartment and (2) the kinesin-2 motor KIF17 into the ciliary compartment. Using the pore-clogging technique, we find that forced dimerization of NUP62 attenuated the gated entry of cytosolic proteins but did not affect entry of membrane proteins or diffusional entry of small cytosolic proteins. We propose a model in which active transport of cytosolic proteins into both nuclear and ciliary compartments requires functional NUPs of the central pore, whereas lateral entry of membrane proteins utilizes a different mechanism that is likely specific to each organelle's limiting membrane.

Asymmetric distribution of dynamic calcium signals in the node of mouse embryo during left-right axis formation

In the node of mouse embryo, rotational movements of cilia generate an external liquid flow known as nodal flow, which determines left-right asymmetric gene expression. How nodal flow is converted into asymmetric gene expression is still controversial, but the increase of Ca(2+) levels in endodermal cells to the left of the node has been proposed to play a role. However, Ca(2+) signals inside the node itself have not yet been described. By our optimized Ca(2+) imaging method, we were able to observe dynamic Ca(2+) signals in the node in live mouse embryos. Pharmacological disruption of Ca(2+) signals did not affect ciliary movements or nodal flow, but did alter the expression patterns of the Nodal and Cerl-2 genes. Quantitative analyses of Ca(2+) signal frequencies and distributions showed that during left-right axis establishment, formerly symmetric Ca(2+) signals became biased to the left side. In iv/iv mutant embryos that showed randomized laterality due to ciliary immotility, Ca(2+) signals were found to be variously left-sided, right-sided, or bilateral, and thus symmetric on average. In Pkd2 mutant embryos, which lacked polycystin-2, a Ca(2+)-permeable cation channel necessary for left-right axis formation, the Ca(2+) signal frequency was lower than in wild-type embryos. Our data support a model in which dynamic Ca(2+) signals in the node are involved in left-right patterning.

High-speed imaging of amoeboid movements using light-sheet microscopy

Light-sheet microscopy has been developed as a powerful tool for live imaging in biological studies. The efficient illumination of specimens using light-sheet microscopy makes it highly amenable to high-speed imaging. We therefore applied this technology to the observation of amoeboid movements, which are too rapid to capture with conventional microscopy. To simplify the setup of the optical system, we utilized the illumination optics from a conventional confocal laser scanning microscope. Using this set-up we achieved high-speed imaging of amoeboid movements. Three-dimensional images were captured at the recording rate of 40 frames/s and clearly outlined the fine structures of fluorescent-labeled amoeboid cellular membranes. The quality of images obtained by our system was sufficient for subsequent quantitative analysis for dynamics of amoeboid movements. This study demonstrates the application of light-sheet microscopy for high-speed imaging of biological specimens.

X-ray diffraction recording from single axonemes of eukaryotic flagella

We report the first X-ray diffraction patterns recorded from single axonemes of eukaryotic flagella with a diameter of only <0.2 μm, by using the technique of cryomicrodiffraction. A spermatozoon isolated from the testis of a fruit fly, Drosophila melanogaster, either intact or demembranated, was mounted straight in a glass capillary, quickly frozen and its 800-μm segment was irradiated end-on with intense synchrotron radiation X-ray microbeams (diameter, ~2 μm) at 74 K. Well-defined diffraction patterns were recorded, consisting of a large number of isolated reflection spots, extending up to 1/5 nm(-1). These reflections showed a tendency to peak every 20°, i.e., the patterns had features of an 18-fold rotational symmetry as expected from the 9-fold rotational symmetry of axonemal structure. This means that the axonemes remain untwisted, even after the manual mounting procedure. The diffraction patterns were compared with the results of model calculations based on a published electron micrograph of the Drosophila axoneme. The comparison provided information about the native state of axoneme, including estimates of axonemal diameter, interdoublet spacing, and masses of axonemal components relative to those of microtubules (e.g., radial spokes, dynein arms, and proteins associated with accessory singlet microtubules). When combined with the genetic resource of Drosophila, the technique presented here will serve as a powerful tool for studying the structure-function relationship of eukaryotic flagella in general.

Geometry-specific heterogeneity of the apparent diffusion rate of materials inside sperm cells

In sea urchin spermatozoa, the energy source powering flagellar motion is provided as ATP produced by mitochondria located at the proximal ends of flagella. However, the bottleneck structure between the sperm head and the flagellar tail seems to restrict the free entry of ATP from mitochondria into the tail region. To test this possibility, we investigated the diffusion properties in sperm cells using fluorescence recovery after photobleaching. We found that the rate of fluorescence recovery in the head region was approximately 10% of that observed in the flagellar tail regions. We also found that, even within the tail region, rates varied depending on location, i.e., rates were slower at the more distal regions. Using computational analysis, the rate heterogeneity was shown to be caused mainly by the geometry of the sperm structure, even if little or no difference in diffusion rates through the neck region was assumed. Therefore, we concluded that materials such as ATP would generally diffuse freely between the heads and the flagella of sperm cells. We believe these findings regarding the diffusion properties inside spermatozoa provide further insights into material transportation and chemical signaling inside eukaryotic cilia and flagella.

Quick shear-flow alignment of biological filaments for X-ray fiber diffraction facilitated by methylcellulose

X-ray fiber diffraction is one of the most useful methods for examining the structural details of live biological filaments under physiological conditions. To investigate biologically active or labile materials, it is crucial to finish fiber alignment within seconds before diffraction analysis. However, the conventional methods, e.g., magnetic field alignment and low-speed centrifugations, are time-consuming and not very useful for such purposes. Here, we introduce a new alignment method using a rheometer with two parallel disks, which was applied to observe fiber diffractions of axonemes, tobacco mosaic tobamovirus, and microtubules. We found that fibers were aligned within 5 s by giving high shear flow (1000-5000 s(-1)) to the medium and that methylcellulose contained in the medium (approximately 1%) was essential to the accomplishment of uniform orientation with a small angular deviation (<5 degrees). The new alignment method enabled us to execute structure analyses of axonemes by small-angle x-ray diffraction. Since this method was also useful for the quick alignment of purified microtubules, as well as tobacco mosaic tobamovirus, we expect that we can apply it to the structural analysis of many other biological filaments.

FRAP analysis of molecular diffusion inside sea-urchin spermatozoa

In sea-urchin spermatozoa, energy required for flagellar motility is provided by ATP diffusion from mitochondria located at the proximal ends of the flagella along with the creatine shuttle system. However, no direct analysis of the diffusion rates inside flagella has been carried out thus far. Using a FRAP (fluorescence recovery after photobleaching) technique, we determined the diffusion coefficients of fluorescein-derivatives (calcein, carboxyfluorescein and Oregon Green) to be 63-64 microm2 s(-1). Although these values are about one third of the estimates that were previously used for theoretical calculations, we concluded that the rate of ATP diffusion inside spermatozoa was high enough to support the continuous motility of sea-urchin sperm flagella if the creatine shuttle system is working. We also investigated the diffusion rate through the ;neck' region between the head and tail. When the head region of a calcein-loaded spermatozoon was photobleached, slow recovery of head fluorescence along with the decrease of fluorescence signal in the tail region was observed. It suggests that small molecules such as calcein (Mr, 622.54) can move beyond the boundary between the head and the flagellum. We expect that these findings regarding the diffusion properties inside spermatozoa will provide us with more general insights into the energy equilibrium and material transportation by passive diffusion inside eukaryotic cilia and flagella.