The history of the birth of the Asakura-Oosawa theory

The history of the birth of the Asakura-Oosawa theory is presented.

Label-free microscopy of mitotic chromosomes using the polarization orthogonality breaking technique

We report how a recently developed polarization imaging technique, implementing micro-wave photonics and referred to as orthogonality-breaking (OB) imaging, can be adapted on a classical confocal fluorescence microscope, and is able to provide informative polarization images from a single scan of the cell sample. For instance, the comparison of the images of various cell lines at different cell-cycle stages obtained by OB polarization microscopy and fluorescence confocal images shows that an endogenous polarimetric contrast arizes with this instrument on compacted chromosomes during cell division.

Chromosomal instability: Stretching the role of checkpoint silencing

Microtubule attachments to kinetochores cause their deformation - a murky phenomenon known as intra-kinetochore stretching. A new study proposes that intra-kinetochore stretching is independent of microtubule-pulling forces and mediates efficient spindle assembly checkpoint silencing to prevent chromosomal instability.

Self-organization of spindle-like microtubule structures

Microtubule self-organization is an essential physical process underlying several essential cellular functions, including cell division. In cell division, the dominant arrangement is the mitotic spindle, a football-shaped microtubule-based machine responsible for separating the chromosomes. We are interested in the underlying fundamental principles behind the self-organization of the spindle shape. Prior biological works have hypothesized that motor proteins control the proper formation of the spindle. Many of these motor proteins are also microtubule-crosslinkers, so it is unclear if the critical aspect is the motor activity or the crosslinking. In this study, we seek to address this question by examining the self-organization of microtubules using crosslinkers alone. We use a minimal system composed of tubulin, an antiparallel microtubule-crosslinking protein, and a crowding agent to explore the phase space of organizations as a function of tubulin and crosslinker concentration. We find that the concentration of the antiparallel crosslinker, MAP65, has a significant effect on the organization and resulted in spindle-like arrangements at relatively low concentration without the need for motor activity. Surprisingly, the length of the microtubules only moderately affects the equilibrium phase. We characterize both the shape and dynamics of these spindle-like organizations. We find that they are birefringent homogeneous tactoids. The microtubules have slow mobility, but the crosslinkers have fast mobility within the tactoids. These structures represent a first step in the recapitulation of self-organized spindles of microtubules that can be used as initial structures for further biophysical and active matter studies relevant to the biological process of cell division.

Effect of RNA interference of the expression of HMGA2 on the proliferation and invasion ability of ACHN renal cell carcinoma cells

This aim of the present study was to observe the effect of high mobility group AT-hook 2 (HMGA2) on the proliferation and invasion ability of ACHN renal cell carcinoma (RCC) cells. Human ACHN cells, an RCC cell line, and HKC normal human renal tubular epithelial cells were cultured. HMGA2 small interfering (si)RNA, Mock-siRNA and their negative control group were designed and synthesized. Subsequently, the ACHN cells were transiently transfected using RNA interference technology. Finally, the mRNA and protein expression levels of HMGA2 were detected using reverse transcription-polymerase chain reaction and western blot analyses. The proliferation ability of the ACHN cells was determined using MTT, and ACHN cell invasion ability was detected using the Transwell method. The results showed that the mRNA and protein expression levels of HMGA2 in the ACHN cells were considerably higher, compared with those in the HKC cells (P<0.01). The RCC cells, in which the expression of HMGA2 was specifically silenced, was successfully constructed. The proliferation rate of cells in the HMGA2-siRNA group was significantly lower, compared with that of cells in the Mock-siRNA group and control group at 24, 48, 72 and 96 h post-transfection (P<0.05). The invasion ability of cells in the HMGA2-siRNA group was significantly lower, compared with that of cells in the Mock-siRNA group and control group (P<0.05) 48 h following transfection. Therefore, the HMGA2 gene may function as an oncogene in the occurrence and development of RCC, and provide specific targets for the targeted therapy of RCC. Further detailed investigations of the HMGA2 gene are important for future gene therapy of RCC.

Polarization resolved second harmonic microscopy

Second harmonic (SH) microscopy has proven to be a powerful imaging modality over the past years due to its intrinsic advantages as a multiphoton process with endogenous contrast specificity, which allows pinhole-less optical sectioning, non-invasive observation, deep tissue penetration, and the possibility of easier signal detection at visible wavelengths. Depending on the relative orientation between the polarization of the incoming light and the second-order susceptibility of non-centrosymmetric structures, SH microscopy provides the unique capacity to probe the absolute molecular structure of a broad variety of biological tissues without the necessity for additional labeling. In addition, SH microscopy, when working with polarimetry, provides clear and in-depth insights on the details of molecular orientation and structural symmetry. In this review, the working principles of the polarization resolving techniques and the corresponding implements of SH microscopy are elucidated, with focus on Stokes vector based polarimetry. An overview of the advancements on SH anisotropy measurements are also presented. Specifically, the recent progresses on the following three topics in polarization resolved SH microscopy will be elucidated, which include Stokes vector resolving for imaging molecular structure and orientation, 3-D structural chirality by SH circular dichroism, and correlation with fluorescence lifetime imaging (FLIM) for in vivo wound healing diagnosis. The potentials and challenges for future researches in exploring complex biological tissues are also discussed.

Expression of tubulin folding cofactor B in mouse hepatic ischemia-reperfusion injury

The aim of the present study was to investigate the association between tubulin folding cofactor B (TBCB) expression and ischemia-reperfusion injury (IRI) in mice. A total of 48 C57BL/6 mice were randomly divided into a control group (Sham, n=6) and an ischemia-reperfusion group (n=42). The ischemia-reperfusion group was further divided into 6 subgroups as per different times after reperfusion (2, 4, 6, 8, 12 and 24 h), with 7 mice per subgroup. A hepatic IRI model was established in mice by clamping the hepatic hilum. Morphology, serum levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), interleukin 6 (IL-6) and tumor necrosis factor-α (TNF-α), and the expression level of TBCB were detected. Compared with the control group, the livers from the ischemia-reperfusion group were significantly changed, particularly at 12 h following ischemia-reperfusion, with obvious hepatic cell degeneration and necrosis. The ALT, AST, IL-6 and TNF-α levels in the sera of the mice in the hepatic ischemia-reperfusion group were increased at all time points following ischemia-reperfusion, and were the highest at 12 h, demonstrating statistically significant differences when compared with the control group (P<0.05). Furthermore, the expression levels of TBCB, TNF-α and IL-6 were significantly increased at all time-points following ischemia-reperfusion, and were the most significant at 12 h. At 24 h following ischemia-reperfusion, the expression levels had decreased. The present study indicated that TBCB expression is associated with TNF-α and IL-6 expression levels in mice with hepatic ischemia-reperfusion, and may be key in the development of liver injury during ischemia-reperfusion in mice.

Living Cells and Dynamic Molecules Observed with the Polarized Light Microscope: the Legacy of Shinya Inoué

In 1948, Shinya Inoué arrived in the United States for graduate studies at Princeton. A year later he came to Woods Hole, starting a long tradition of summer research at the Marine Biological Laboratory (MBL), which quickly became Inoué's scientific home. Primed by his Japanese mentor, Katsuma Dan, Inoué followed Dan's mantra to work with healthy, living cells, on a fundamental problem (mitosis), with a unique tool set that he refined for precise and quantitative observations (polarized light microscopy), and a fresh and brilliant mind that was unafraid of challenging current dogma. Building on this potent combination, Inoué contributed landmark observations and concepts in cell biology, including the notion that there are dynamic, fine structures inside living cells, in which molecular assemblies such as mitotic spindle fibers exist in delicate equilibrium with their molecular building blocks suspended in the cytoplasm. In the late 1970s and 1980s, Inoué and others at the MBL were instrumental in conceiving video microscopy, a groundbreaking technique which married light microscopy and electronic imaging, ushering in a revolution in how we know and what we know about living cells and the molecular mechanisms of life. Here, we recount some of Inoué's accomplishments and describe how his legacy has shaped current activities in polarized light imaging at the MBL.

Microtubule-Binding Proteins as Promising Biomarkers of Paclitaxel Sensitivity in Cancer Chemotherapy

Microtubules, tirelessly animated and highly dynamic structures, are vital for most cellular processes and their intricacies are still being revealed even after a century since their discovery. The importance of microtubules as chemotherapeutic targets cannot be overstated, and their clinical role is unlikely to abate in the near future. Indeed, improved understanding of microtubule biology could herald a new epoch of anticancer drug design by permitting fine-tuning of microtubule-targeting agents, the clinical utility of which is presently often limited by primary or acquired resistance. Paclitaxel, one such agent belonging to the taxane family, has proven a resoundingly successful treatment for many cancer patients; however, for too many others with paclitaxel-refractory tumors, the drug has offered nothing but side effects. Accumulating evidence suggests that microtubule-binding proteins (MBPs) can regulate paclitaxel sensitivity in a wide range of cancer types. Improved understanding of how these proteins can be assayed to predict treatment responses or manipulated pharmacologically to improve clinical outcomes could transform modern chemotherapy and is urgently awaited.

Liquid-liquid phase separation in biology

Cells organize many of their biochemical reactions in non-membrane compartments. Recent evidence has shown that many of these compartments are liquids that form by phase separation from the cytoplasm. Here we discuss the basic physical concepts necessary to understand the consequences of liquid-like states for biological functions.

XMAP215 activity sets spindle length by controlling the total mass of spindle microtubules

Metaphase spindles are microtubule-based structures that use a multitude of proteins to modulate their morphology and function. Today, we understand many details of microtubule assembly, the role of microtubule-associated proteins, and the action of molecular motors. Ultimately, the challenge remains to understand how the collective behaviour of these nanometre-scale processes gives rise to a properly sized spindle on the micrometre scale. By systematically engineering the enzymatic activity of XMAP215, a processive microtubule polymerase, we show that Xenopus laevis spindle length increases linearly with microtubule growth velocity, whereas other parameters of spindle organization, such as microtubule density, lifetime and spindle shape, remain constant. We further show that mass balance can be used to link the global property of spindle size to individual microtubule dynamic parameters. We propose that spindle length is set by a balance of non-uniform nucleation and global microtubule disassembly in a liquid-crystal-like arrangement of microtubules.

Tubulin cofactor A functions as a novel positive regulator of ccRCC progression, invasion and metastasis

Microtubules (Mts), which consist of α/β-tubulin heterodimers, are involved in cancer development and metastasis. Tubulin cofactor A (TBCA) plays crucial roles in modulating tubulin folding and α/β-tubulin heterodimer polymerization. Here, we identified the aberrant expression of TBCA in clear cell renal cell carcinoma (ccRCC) specimens as well as cell lines and revealed the function of TBCA as a novel positive regulator in ccRCC progression, invasion and metastasis. qRT-PCR, Western blot and immunohistochemistry assays confirmed that TBCA was significantly highly expressed in ccRCC specimens and cell lines compared to their corresponding normal kidney tissues and HKC. Accordingly, the influence of TBCA on cell proliferation, apoptosis and invasion/migration was detected through overexpression and knockdown of endogenous TBCA protein level in ccRCC cells via plasmids. Silencing of TBCA expression inhibited the proliferation of 786-O cells and Caki-1 cells and promoted the apoptosis of 786-O cells. Down-regulation of TBCA expression also reduced the invasion and migration ability of 786-O cells. Interestingly, overexpression of TBCA did not induce biocharacteristics that directly contrasted to those of TBCA knockdown. Importantly, exploration of the mechanism showed that TBCA could function via modulating cytoskeleton integration and influencing cell cycle progress. Furthermore, down-regulation of TBCA expression in 786-O and Caki-1 cells affected cytoskeleton integration and cell size, induced S/G2 cell cycle arrest and led to cyclineA/E and CDK2 aberrant expression. By investigating novel roles of TBCA in regulation of ccRCC cell progression, invasion and metastasis, our study identified that TBCA may be a potential molecular target for ccRCC therapy.

Visualization and analysis of 3D microscopic images

In a wide range of biological studies, it is highly desirable to visualize and analyze three-dimensional (3D) microscopic images. In this primer, we first introduce several major methods for visualizing typical 3D images and related multi-scale, multi-time-point, multi-color data sets. Then, we discuss three key categories of image analysis tasks, namely segmentation, registration, and annotation. We demonstrate how to pipeline these visualization and analysis modules using examples of profiling the single-cell gene-expression of C. elegans and constructing a map of stereotyped neurite tracts in a fruit fly brain.

Shinya Inoue: lighting the way in microscopy. Interviewed by Caitlin Sedwick

Inoué’s innovations in polarized light microscopy allowed the first documentation of the mitotic spindle in living cells.

Control of mitotic spindle length

The mitotic spindle accurately segregates genetic instructions by moving chromosomes to spindle poles (anaphase A) and separating the poles (anaphase B) so that, in general, the chromosomes and poles are positioned near the centers of the nascent daughter cell products of each cell division. Because the size of different types of dividing cells, and thus the spacing of their daughter cell centers, can vary significantly, the length of the metaphase or postanaphase B spindle often scales with cell size. However, significant exceptions to this scaling rule occur, revealing the existence of cell size&#x2013;independent, spindle-associated mechanisms of spindle length control. The control of spindle length reflects the action of mitotic force-generating mechanisms, and its study may illuminate general principles by which cells regulate the size of internal structures. Here we review molecules and mechanisms that control spindle length, how these mechanisms are deployed in different systems, and some quantitative models that describe the control of spindle length.

Assessment of mitotic spindle phenotypes in Drosophila S2 cells

The Drosophila S2 cell line is popularly used to study mitosis. In this cell line, multiple genes can be easily and efficiently knocked down by RNA interference (RNAi), and the associated mitotic phenotypes can be assessed with high-resolution microscopy after immunofluorescence or in a living cell. However, compared to untransformed cells in wild-type organisms such as yeasts or worms, mitosis in the S2 cell line is more variable and often looks abnormal even in RNAi-untreated cells. Therefore, in order to judge whether a phenotype is derived from RNAi of the target gene or is simply a variation of control cells, it is critical to prepare proper control samples and perform objective imaging and image analysis. Here, we discuss how bona fide mitotic phenotypes associated with RNAi can be identified, avoiding selecting false positives, in S2 cells.