Anillin forms linear structures and facilitates furrow ingression after septin and formin depletion.

During cytokinesis, a contractile ring consisting of unbranched filamentous actin (F-actin) and myosin II constricts at the cell equator. Unbranched F-actin is generated by formin, and without formin no cleavage furrow forms. In Caenorhabditis elegans, depletion of septin restores furrow ingression in formin mutants. How the cleavage furrow ingresses without a detectable unbranched F-actin ring is unknown. We report that, in this setting, anillin (ANI-1) forms a meshwork of circumferentially aligned linear structures decorated by non-muscle myosin II (NMY-2). Analysis of ANI-1 deletion mutants reveals that its disordered N-terminal half is required for linear structure formation and sufficient for furrow ingression. NMY-2 promotes the circumferential alignment of the linear ANI-1 structures and interacts with various lipids, suggesting that NMY-2 links the ANI-1 network with the plasma membrane. Collectively, our data reveal a compensatory mechanism, mediated by ANI-1 linear structures and membrane-bound NMY-2, that promotes furrowing when unbranched F-actin polymerization is compromised.

Apical-basal polarity of the spectrin cytoskeleton in the C. elegans vulva.

The C. elegans vulva is a polarized epithelial tube that has been studied extensively as a model for cell-cell signaling, cell fate specification, and tubulogenesis. Here we used endogenous fusions to show that the spectrin cytoskeleton is polarized in this organ, with conventional beta-spectrin ( UNC-70 ) found only at basolateral membranes and beta heavy spectrin ( SMA-1 ) found only at apical membranes. The sole alpha-spectrin ( SPC-1 ) is present at both locations but requires SMA-1 for its apical localization. Thus, beta spectrins are excellent markers for vulva cell membranes and polarity.

ß-heavy-spectrin stabilizes the constricting contractile ring during cytokinesis.

Cytokinesis requires the constriction of an actomyosin-based contractile ring and involves multiple F-actin crosslinkers. We show that partial depletion of the C. elegans cytokinetic formin generates contractile rings with low F-actin levels that constrict but are structurally fragile, and we use this background to investigate the roles of the crosslinkers plastin/PLST-1 and ß-heavy-spectrin/SMA-1 during ring constriction. We show that the removal of PLST-1 or SMA-1 has opposite effects on the structural integrity of fragile rings. PLST-1 loss reduces cortical tension that resists ring constriction and makes fragile rings less prone to ruptures and regressions, whereas SMA-1 loss exacerbates structural defects, leading to frequent ruptures and cytokinesis failure. Fragile rings without SMA-1 or containing a shorter SMA-1, repeatedly rupture at the same site, and SMA-1::GFP accumulates at repair sites in fragile rings and in rings cut by laser microsurgery. These results establish that ß-heavy-spectrin stabilizes the constricting ring and reveals the importance of ß-heavy-spectrin size for network connectivity at low F-actin density.

Subcellular localization of mutant P23H rhodopsin in an RFP fusion knock-in mouse model of retinitis pigmentosa.

The P23H mutation in rhodopsin (Rho), the rod visual pigment, is the most common allele associated with autosomal-dominant retinitis pigmentosa (adRP). The fate of misfolded mutant Rho in rod photoreceptors has yet to be elucidated. We generated a new mouse model, in which the P23H-Rho mutant allele is fused to the fluorescent protein Tag-RFP-T (P23HhRhoRFP). In heterozygotes, outer segments formed, and wild-type (WT) rhodopsin was properly localized, but mutant P23H-Rho protein was mislocalized in the inner segments. Heterozygotes exhibited slowly progressing retinal degeneration. Mislocalized P23HhRhoRFP was contained in greatly expanded endoplasmic reticulum (ER) membranes. Quantification of mRNA for markers of ER stress and the unfolded protein response revealed little or no increases. mRNA levels for both the mutant human rhodopsin allele and the WT mouse rhodopsin were reduced, but protein levels revealed selective degradation of the mutant protein. These results suggest that the mutant rods undergo an adaptative process that prolongs survival despite unfolded protein accumulation in the ER. The P23H-Rho-RFP mouse may represent a useful tool for the future study of the pathology and treatment of P23H-Rho and adRP. This article has an associated First Person interview with the first author of the paper.

Plastin and spectrin cooperate to stabilize the actomyosin cortex during cytokinesis.

Cytokinesis, the process that partitions the mother cell into two daughter cells, requires the assembly and constriction of an equatorial actomyosin network. Different types of non-motor F-actin crosslinkers localize to the network, but their functional contribution remains poorly understood. Here, we describe a synergy between the small rigid crosslinker plastin and the large flexible crosslinker spectrin in the C. elegans one-cell embryo. In contrast to single inhibitions, co-inhibition of plastin and the ßH-spectrin (SMA-1) results in cytokinesis failure due to progressive disorganization and eventual collapse of the equatorial actomyosin network. Cortical localization dynamics of non-muscle myosin II in co-inhibited embryos mimic those observed after drug-induced F-actin depolymerization, suggesting that the combined action of plastin and spectrin stabilizes F-actin in the contractile ring. An in silico model predicts that spectrin is more efficient than plastin at stabilizing the ring and that ring formation is relatively insensitive to ßH-spectrin length, which is confirmed in vivo with a sma-1 mutant that lacks 11 of its 29 spectrin repeats. Our findings provide the first evidence that spectrin contributes to cytokinesis and highlight the importance of crosslinker interplay for actomyosin network integrity.

Fragmented Politics in Hong Kong-Analyzing the Pro-democracy Cohesion in the Legislative Council Before 2019.

This study is to analyze how the fragmentation of the pro-democracy camp affected their council voting and policy stances before 2019. The quantitative measurements including the rice and unity indices are adopted to evaluate the cohesions of the pro-Beijing and pro-democracy camps in bill voting, in which the strategies employed by the pro-democracy camp are further analyzed. Before the 2010s, the moderate democrats deliberately separated from the administration and some of them also kept distance from the radical groups. However, since the radical ideologies gained supports from time to time, the moderate democrats had been forced to follow more pro-active lines against the administration. Although the political sphere of Hong Kong has drastically changed after the 2019 Anti-extradition Protests, the cohesion of the pro-democracy parties in the previous terms of the Legislative Council still facilitates to understand the legislative process in the city. In this article, 18 then members of the Legislative Council from different parties were interviewed in 2018, providing various insights on the analysis of pro-democracy cohesion and fragmented politics in Hong Kong.

Equatorial Non-muscle Myosin II and Plastin Cooperate to Align and Compact F-actin Bundles in the Cytokinetic Ring.

Cytokinesis is the last step of cell division that physically partitions the mother cell into two daughter cells. Cytokinesis requires the assembly and constriction of a contractile ring, a circumferential array of filamentous actin (F-actin), non-muscle myosin II motors (myosin), and actin-binding proteins that forms at the cell equator. Cytokinesis is accompanied by long-range cortical flows from regions of relaxation toward regions of compression. In the C. elegans one-cell embryo, it has been suggested that anterior-directed cortical flows are the main driver of contractile ring assembly. Here, we use embryos co-expressing motor-dead and wild-type myosin to show that cortical flows can be severely reduced without major effects on contractile ring assembly and timely completion of cytokinesis. Fluorescence recovery after photobleaching in the ingressing furrow reveals that myosin recruitment kinetics are also unaffected by the absence of cortical flows. We find that myosin cooperates with the F-actin crosslinker plastin to align and compact F-actin bundles at the cell equator, and that this cross-talk is essential for cytokinesis. Our results thus argue against the idea that cortical flows are a major determinant of contractile ring assembly. Instead, we propose that contractile ring assembly requires localized concerted action of motor-competent myosin and plastin at the cell equator.

Mental health nurses in non-uniform: Facilitator of recovery process?

WHAT IS KNOWN ON THE SUBJECT?: Many Western countries have abandoned the wearing of nurse uniforms on inpatient mental health wards. The adoption of a non-uniform policy in Hong Kong was recently introduced in select rehabilitation units to align with the philosophy of the recovery model. WHAT THE PAPER ADDS TO EXISTING KNOWLEDGE?: The findings suggest that nurses perceived wearing non-uniform might help to reduce the self-stigma of service users and develop better self-esteem. The perceived potential benefits of the introduction of a non-uniform policy seemed to outweigh the perceived drawbacks. WHAT ARE THE IMPLICATIONS FOR PRACTICE?: The results further acknowledge the potential positive effects of nurses wearing non-uniform on facilitating psychiatric service users' recovery process. However, further research on service users' perspectives is required. The wearing of non-uniform may be considered to be extended to other psychiatric wards in Hong Kong and other similar Asian settings in order to potentially help promote patient's recovery and to reduce emotional distance between staff and service users. ABSTRACT: Introduction A non-uniform policy was recently adopted in selected Hong Kong rehabilitation wards to align with the philosophy of the recovery model. The change in policy is relatively novel in Asia, where no previous studies have reported how this may influence nursing care and service users' recovery. Aim To explore Hong Kong Mental Health Nurses' views about wearing non-uniform within an inpatient rehabilitation unit in regard to facilitating service users' recovery process. Method A qualitative descriptive study was conducted, utilizing individual in-depth semi-structured research interviews. Results A total of 12 interviews were conducted with nurse participants. The analysis process identified 3 main themes and 9 subthemes. Main themes were "building up rapport with service users," "non-uniform helps deinstitutionalization" and "different approaches to maximize the benefit and to minimize the risk." Discussion Despite some concerns, the majority of nurse participants positively viewed the policy of wearing non-uniform and felt it was potentially beneficial to service users' recovery process. Implications for practice Nurses perceived that wearing non-uniform may facilitate meaningful therapeutic engagement, and may help to reduce the self-stigma and develop the self-esteem of service users. Other inpatient units in Hong Kong and similar Asian settings might consider adopting the policy.

Using the Four-Cell C. elegans Embryo to Study Contractile Ring Dynamics During Cytokinesis.

Cytokinesis is the process that completes cell division by partitioning the contents of the mother cell between the two daughter cells. It involves the highly regulated assembly and constriction of an actomyosin contractile ring, whose function is to pinch the mother cell in two. Research on the contractile ring has particularly focused on the signaling mechanisms that dictate when and where the ring is formed. In vivo studies of ring constriction are however scarce and its mechanistic understanding is therefore limited. Here we present several experimental approaches for monitoring ring constriction in vivo, using the four-cell C. elegans embryo as model. These approaches allow for the ring to be perturbed only after it forms and include the combination of live imaging with acute drug treatments, temperature-sensitive mutants and rapid temperature shifts, as well as laser microsurgery. In addition, we explain how to combine these with RNAi-mediated depletion of specific components of the cytokinetic machinery.

Crosslinking activity of non-muscle myosin II is not sufficient for embryonic cytokinesis in C. elegans.

Cytokinesis in animal cells requires the assembly and constriction of a contractile actomyosin ring. Non-muscle myosin II is essential for cytokinesis, but the role of its motor activity remains unclear. Here, we examine cytokinesis in C. elegans embryos expressing non-muscle myosin motor mutants generated by genome editing. Two non-muscle motor-dead myosins capable of binding F-actin do not support cytokinesis in the one-cell embryo, and two partially motor-impaired myosins delay cytokinesis and render rings more sensitive to reduced myosin levels. Further analysis of myosin mutants suggests that it is myosin motor activity, and not the ability of myosin to crosslink F-actin, that drives the alignment and compaction of F-actin bundles during contractile ring assembly, and that myosin motor activity sets the pace of contractile ring constriction. We conclude that myosin motor activity is required at all stages of cytokinesis. Finally, characterization of the corresponding motor mutations in C. elegans major muscle myosin shows that motor activity is required for muscle contraction but is dispensable for F-actin organization in adult muscles.This article has an associated 'The people behind the papers' interview.

The ARP2/3 complex prevents excessive formin activity during cytokinesis.

Cytokinesis completes cell division by constriction of an actomyosin contractile ring that separates the two daughter cells. Here we use the early Caenorhabditis elegans embryo to explore how the actin filament network in the ring and the surrounding cortex is regulated by the single cytokinesis formin CYK-1 and the ARP2/3 complex, which nucleate nonbranched and branched filaments, respectively. We show that CYK-1 and the ARP2/3 complex are the predominant F-actin nucleators responsible for generating distinct cortical F-actin architectures and that depletion of either nucleator affects the kinetics of cytokinesis. CYK-1 is critical for normal F-actin levels in the contractile ring, and acute inhibition of CYK-1 after furrow ingression slows ring constriction rate, suggesting that CYK-1 activity is required throughout ring constriction. Surprisingly, although the ARP2/3 complex does not localize in the contractile ring, depletion of the ARP2 subunit or treatment with ARP2/3 complex inhibitor delays contractile ring formation and constriction. We present evidence that the delays are due to an excess in formin-nucleated cortical F-actin, suggesting that the ARP2/3 complex negatively regulates CYK-1 activity. We conclude that the kinetics of cytokinesis are modulated by interplay between the two major actin filament nucleators.

Morphological changes of the optic lobe from late embryonic to adult stages in oval squids Sepioteuthis lessoniana.

The optic lobe is the largest brain area within the central nervous system of cephalopods and it plays important roles in the processing of visual information, the regulation of body patterning, and locomotive behavior. The oval squid Sepioteuthis lessoniana has relatively large optic lobes that are responsible for visual communication via dynamic body patterning. It has been observed that the visual behaviors of oval squids change as the animals mature, yet little is known about how the structure of the optic lobes changes during development. The aim of the present study was to characterize the ontogenetic changes in neural organization of the optic lobes of S. lessoniana from late embryonic stage to adulthood. Magnetic resonance imaging and micro-CT scans were acquired to reconstruct the 3D-structure of the optic lobes and examine the external morphology at different developmental stages. In addition, optic lobe slices with nuclear staining were used to reveal changes in the internal morphology throughout development. As oval squids mature, the proportion of the brain making up the optic lobes increases continuously, and the optic lobes appear to have a prominent dent on the ventrolateral side. Inside the optic lobe, the cortex and the medulla expand steadily from the late embryonic stage to adulthood, but the cell islands in the tangential zone of the optic lobe decrease continuously in parallel. Interestingly, the size of the nuclei of cells within the medulla of the optic lobe increases throughout development. These findings suggest that the optic lobe undergoes continuous external morphological change and internal neural reorganization throughout the oval squid's development. These morphological changes in the optic lobe are likely to be responsible for changes in the visuomotor behavior of oval squids from hatching to adulthood.

Sorting nexin 3 mutation impairs development and neuronal function in Caenorhabditis elegans.

The sorting nexins family of proteins (SNXs) plays pleiotropic functions in protein trafficking and intracellular signaling and has been associated with several disorders, namely Alzheimer's disease and Down's syndrome. Despite the growing association of SNXs with neurodegeneration, not much is known about their function in the nervous system. The aim of this work was to use the nematode Caenorhabditis elegans that encodes in its genome eight SNXs orthologs, to dissect the role of distinct SNXs, particularly in the nervous system. By screening the C. elegans SNXs deletion mutants for morphological, developmental and behavioral alterations, we show here that snx-3 gene mutation leads to an array of developmental defects, such as delayed hatching, decreased brood size and life span and reduced body length. Additionally, ∆snx-3 worms present increased susceptibility to osmotic, thermo and oxidative stress and distinct behavioral deficits, namely, a chemotaxis defect which is independent of the described snx-3 role in Wnt secretion. ∆snx-3 animals also display abnormal GABAergic neuronal architecture and wiring and altered AIY interneuron structure. Pan-neuronal expression of C. elegans snx-3 cDNA in the ∆snx-3 mutant is able to rescue its locomotion defects, as well as its chemotaxis toward isoamyl alcohol. Altogether, the present work provides the first in vivo evidence of the SNX-3 role in the nervous system.

A Thiazole Orange Derivative Targeting the Bacterial Protein FtsZ Shows Potent Antibacterial Activity.

The prevalence of multidrug resistance among clinically significant bacteria calls for the urgent development of new antibiotics with novel mechanisms of action. In this study, a new small molecule exhibiting excellent inhibition of bacterial cell division with potent antibacterial activity was discovered through cell-based screening. The compound exhibits a broad spectrum of bactericidal activity, including the methicillin-resistant Staphylococcus aureus, vancomycin-resistant Enterococcus and NDM-1 Escherichia coli. The in vitro and in vivo results suggested that this compound disrupts the dynamic assembly of FtsZ protein and Z-ring formation through stimulating FtsZ polymerization. Moreover, this compound exhibits no activity on mammalian tubulin polymerization and shows low cytotoxicity on mammalian cells. Taken together, these findings could provide a new chemotype for development of antibacterials with FtsZ as the target.

Efficient Synthesis of Amine-Linked 2,4,6-Trisubstituted Pyrimidines as a New Class of Bacterial FtsZ Inhibitors.

We have recently identified a new class of filamenting temperature-sensitive mutant Z (FtsZ)-interacting compounds that possess a 2,4,6-trisubstituted pyrimidine-quinuclidine scaffold with moderate antibacterial activity. Employing this scaffold as a molecular template, a compound library of amine-linked 2,4,6-trisubstituted pyrimidines with 99 candidates was successfully established by employing an efficient convergent synthesis designed to explore their structure-activity relationship. The results of minimum inhibitory concentration (MIC) assay against Staphylococcus aureus strains and cytotoxicity assay against the mouse L929 cell line identified those compounds with potent antistaphylococcal properties (MIC ranges from 3 to 8 µg/mL) and some extent of cytotoxicity against normal cells (IC50 ranges from 6 to 27 µM). Importantly, three compounds also exhibited potent antibacterial activities against nine clinically isolated methicillin-resistant S. aureus (MRSA) strains. One of the compounds, 14av_amine16, exhibited low spontaneous frequency of resistance, low toxicity against Galleria mellonella larvae, and the ability to rescue G. mellonella larvae (20% survival rate at a dosage of 100 mg/kg) infected with a lethal dose of MRSA ATCC 43300 strain. Biological characterization of compound 14av_amine16 by saturation transfer difference NMR, light scattering assay, and guanosine triphosphatase hydrolysis assay with purified S. aureus FtsZ protein verified that it interacted with the FtsZ protein. Such a property of FtsZ inhibitors was further confirmed by observing iconic filamentous cell phenotype and mislocalization of the Z-ring formation of Bacillus subtilis. Taken together, these 2,4,6-trisubstituted pyrimidine derivatives represent a novel scaffold of S. aureus FtsZ inhibitors.

Normative data for rotational chair stratified by age.

OBJECTIVES/HYPOTHESIS: The purpose of this study is to examine the range of vestibulo-ocular reflex (VOR) gain on rotary chair (RC) testing in subjects without ear and vestibular problems stratified by age and gender. STUDY DESIGN: Prospective cross-sectional study. METHODS: One hundred subjects ranging in age from 6 to 78 years underwent RC testing. VOR gains at frequencies ranging from 0.01 to 0.64 Hz were recorded. The PROC MIXED procedure in SAS was used to analyze differences in VOR gain between gender and the following age groups: group 1 (6-12 years), group 2 (13-17 years), group 3 (18-30 years), group 4 (31-50 years), and group 5 (>50 years). RESULTS: Twenty subjects were recruited for each of the five groups. Group 1 showed the highest average VOR gain compared to all other age groups (P < .05). There was an inverse correlation between VOR gain and age (P < .05). The lowest frequency (0.01 Hz) had the highest correlation between VOR gain and age (r = -0.425; P < .0001). CONCLUSIONS: Our study demonstrates VOR gain differences with age, especially in the preadolescent and geriatric groups. The current manufacturer-provided normative data do not serve as an accurate reference, especially for these two age groups. A larger population of all age groups should be compared to the current RC manufacturer normative values to ensure that they accurately reflect the true normative data. LEVEL OF EVIDENCE: 2.

Antimicrobial activity of a quinuclidine-based FtsZ inhibitor and its synergistic potential with ß-lactam antibiotics.

Filamenting temperature-sensitive mutant Z (FtsZ) is an essential cell division protein that cooperates in the formation of the cytokinetic Z-ring in most bacteria and has thus been recognized as a promising antimicrobial drug target. We have recently used a structure-based virtual screening approach to identify pyrimidine-linked quinuclidines as a novel class of FtsZ inhibitors. In this study, we further investigated the antibacterial properties of one of the most potent compounds (quinuclidine 1) and its synergistic activity with ß-lactam antibiotics. Susceptibility results showed that quinuclidine 1 was active against multiple antibiotic-resistant bacterial strains including methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus faecium with minimal inhibitory concentrations of 24 µg ml(-1). When quinuclidine 1 was combined with ß-lactam antibiotics, synergistic antimicrobial activities against antibiotic-resistant strains of S. aureus were found. Further in vitro studies suggest that prevention of FtsZ protofilament formation by quinuclidine 1 impairs the formation of Z-ring, and thus inhibits bacterial division. These findings open a new approach for development of quinuclidine-based FtsZ inhibitors into potent antimicrobial agents.