Cortical Clustering Research Articles

A novel protein Moat prevents ectopic epithelial folding by limiting Bazooka/Par3-dependent adherens junctions.

Contractile myosin and cell adhesion work together to induce tissue shape changes, but how they are patterned to achieve diverse morphogenetic outcomes remains unclear. Epithelial folding occurs via apical constriction, mediated by apical contractile myosin engaged with adherens junctions, as in Drosophila ventral furrow formation. While it has been shown that a multicellular gradient of myosin contractility determines folding shape, the impact of multicellular patterning of adherens junction levels on tissue folding is unknown. We identified a novel Drosophila genemoat essential for differential apical constriction and folding behaviors across the ventral epithelium which contains both folding ventral furrow and nonfolding ectodermal anterior midgut (ectoAMG). We show that Moat functions to downregulate polarity-dependent adherens junctions through inhibiting cortical clustering of Bazooka/Par3 proteins. Such downregulation of polarity-dependent junctions is critical for establishing a myosin-dependent pattern of adherens junctions, which in turn mediates differential apical constriction in the ventral epithelium. Inmoatmutants, abnormally high levels of polarity-dependent junctions promote ectopic apical constriction in cells with low-level contractile myosin, resulting in expansion of infolding from ventral furrow to ectoAMG, and flattening of ventral furrow constriction gradient. Our results demonstrate that tissue-scale distribution of adhesion levels patterns apical constriction and establishes morphogenetic boundaries.

Mechanics of spindle orientation in human mitotic cells is determined by pulling forces on astral microtubules and clustering of cortical dynein

The forces that orient the spindle in human cells remain poorly understood due to a lack of direct mechanical measurements in mammalian systems. We use magnetic tweezers to measure the force on human mitotic spindles. Combining the spindle's measured resistance to rotation, the speed at which it rotates after laser ablating astral microtubules, and estimates of the number of ablated microtubules reveals that each microtubule contacting the cell cortex is subject to ∼5 pN of pulling force, suggesting that each is pulled on by an individual dynein motor. We find that the concentration of dynein at the cell cortex and extent of dynein clustering are key determinants of the spindle's resistance to rotation, with little contribution from cytoplasmic viscosity, which we explain using a biophysically based mathematical model. This work reveals how pulling forces on astral microtubules determine the mechanics of spindle orientation and demonstrates the central role of cortical dynein clustering.

Synthetic Par polarity induces cytoskeleton asymmetry in unpolarized mammalian cells

Polarized cells rely on a polarized cytoskeleton to function. Yet, how cortical polarity cues induce cytoskeleton polarization remains elusive. Here, we capitalized on recently established designed 2D protein arrays to ectopically engineer cortical polarity of virtually any protein of interest during mitosis in various cell types. This enables direct manipulation of polarity signaling and the identification of the cortical cues sufficient for cytoskeleton polarization. Using this assay, we dissected the logic of the Par complex pathway, a key regulator of cytoskeleton polarity during asymmetric cell division. We show that cortical clustering of any Par complex subunit is sufficient to trigger complex assembly and that the primary kinetic barrier to complex assembly is the relief of Par6 autoinhibition. Further, we found that inducing cortical Par complex polarity induces two hallmarks of asymmetric cell division in unpolarized mammalian cells: spindle orientation, occurring via Par3, and central spindle asymmetry, depending on aPKC activity.

Overexpression of Mdm36 reveals Num1 foci that mediate dynein-dependent microtubule sliding in budding yeast.

The current model for spindle positioning requires attachment of the microtubule (MT) motor cytoplasmic dynein to the cell cortex, where it generates pulling force on astral MTs to effect spindle displacement. How dynein is anchored by cortical attachment machinery to generate large spindle-pulling forces remains unclear. Here, we show that cortical clustering of Num1, the yeast dynein attachment molecule, is limited by its assembly factor Mdm36. Overexpression of Mdm36 results in an overall enhancement of Num1 clustering but reveals a population of dim Num1 clusters that mediate dynein anchoring at the cell cortex. Direct imaging shows that bud-localized, dim Num1 clusters containing around only six Num1 molecules mediate dynein-dependent spindle pulling via a lateral MT sliding mechanism. Mutations affecting Num1 clustering interfere with mitochondrial tethering but do not interfere with the dynein-based spindle-pulling function of Num1. We propose that formation of small ensembles of attachment molecules is sufficient for dynein anchorage and cortical generation of large spindle-pulling forces.This article has an associated First Person interview with the first author of the paper.

Cortical forces and CDC-42 control clustering of PAR proteins for Caenorhabditis elegans embryonic polarization

Cell polarization enables zygotes to acquire spatial asymmetry, which in turn patterns cellular and tissue axes during development. Local modification in the actomyosin cytoskeleton mediates spatial segregation of partitioning-defective (PAR) proteins at the cortex, but how mechanical changes in the cytoskeleton are transmitted to PAR proteins remains elusive. Here we uncover a role of actomyosin contractility in the remodelling of PAR proteins through cortical clustering. During embryonic polarization in Caenorhabditis elegans, actomyosin contractility and the resultant cortical tension stimulate clustering of PAR-3 at the cortex. Clustering of atypical protein kinase C (aPKC) is supported by PAR-3 clusters and is antagonized by activation of CDC-42. Cortical clustering is associated with retardation of PAR protein exchange at the cortex and with effective entrainment of advective cortical flows. Our findings delineate how cytoskeleton contractility couples the cortical clustering and long-range displacement of PAR proteins during polarization. The principles described here would apply to other pattern formation processes that rely on local modification of cortical actomyosin and PAR proteins.

Cortical forces and CDC-42 control clustering of PAR proteins for C. elegans embryonic polarization

Cortical forces and CDC-42 control clustering of PAR proteins for C. elegans embryonic polarization

BrainSync: An Orthogonal Transformation for Synchronization of fMRI Data Across Subjects.

We describe a method that allows direct comparison of resting fMRI (rfMRI) time series across subjects. For this purpose, we exploit the geometry of the rfMRI signal space to conjecture the existence of an orthogonal transformation that synchronizes fMRI time series across sessions and subjects. The method is based on the observation that rfMRI data exhibit similar connectivity patterns across subjects, as reflected in the pairwise correlations between different brain regions. The orthogonal transformation that performs the synchronization is unique, invertible, efficient to compute, and preserves the connectivity structure of the original data for all subjects. Similarly to image registration, where we spatially align the anatomical brain images, this synchronization of brain signals across a population or within subject across sessions facilitates longitudinal and cross-sectional studies of rfMRI data. The utility of this transformation is illustrated through applications to quantification of fMRI variability across subjects and sessions, joint cortical clustering of a population and comparison of task-related and resting fMRI.

Morphological and Histological Studies of Artesunate on the Developing Cerebral Cortex of Wistar Rat Foetuses

The longstanding use of artemisinin and its derivatives, mainly artesunate among pregnant women is recommended as first line treatment for malaria especially in endemic area like Nigeria. The present study investigated the morphological and histological effects of artesunate on the developing cerebral cortex of Wistar rat foetuses. Twenty healthy female Albino Wistar rats of average weight of 165 g were grouped into 4 with each group containing 5 rats. The rats were fed daily and water was allowed ad libitum. The animals were mated overnight with sexually matured males and were separated into different cages after confirmation of pregnancy. Oral doses of 0.2 mg/kg (low dose, LD), 0.4 mg/kg (medium dose, MD) and 0.8 mg/kg (high dose, HD) body weight of artesunate were administered to pregnant rats in LD, MD and HD groups respectively, from the 8th to the 12th day of gestation. Group 1 rats were the control, and received distilled water on the same days. The results showed a significant reduction in the morphometry of some body parts. The mean foetal body weights were 5.33 g, 5.14 g, 4.67 g and 3.78 g in the Control, LD, MD and HD groups respectively, while the mean crown-rump lengths were 3.67 cm, 3.43 cm, 3.00 cm and 3.00 cm in the Control, LD, MD and HD groups respectively. The histological examinations revealed some neurodegenerative changes in the developing cerebral cortex of Wistar rat foetuses. These neurodegenerative changes include reduction in thickness of the cortical zones, cell clustering and chromatolysis of the cells of cerebral cortex. The results showed that artesunate when administered in high dosages could be dangerous to the developing foetuses

Spatiotemporal regulation of chemical reactions by active cytoskeletal remodeling.

Efficient and reproducible construction of signaling and sorting complexes, both on the surface and within the living cell, is contingent on local regulation of biochemical reactions by the cellular milieu. We propose that in many cases this spatiotemporal regulation can be mediated by interaction with components of the dynamic cytoskeleton. We show how the interplay between active contractility and remodeling of the cytoskeleton can result in transient focusing of passive molecules to form clusters, leading to a dramatic increase in the reaction efficiency and output levels. The dynamic cytoskeletal elements that drive focusing behave as quasienzymes catalyzing the chemical reaction. These ideas are directly applicable to the cortical actin-dependent clustering of cell surface proteins such as lipid-tethered GPI-anchored proteins, Ras proteins, as well as many proteins that have domains that confer the ability to interact with the actin cytoskeleton. In general such cytoskeletal driven clustering of proteins could be a cellular mechanism to spatiotemporally regulate and amplify local chemical reaction rates in a variety of contexts such as signaling, transcription, sorting, and endocytosis.

Clustering of atlas-defined cortical regions based on relaxation times and proton density

Magnetic resonance parameters, such as longitudinal (T1) and transverse (T2) relaxation times and proton density (PD) provide intrinsic information about the human brain. In vivo quantification of these parameters may enable detection of subtle regional grey matter (GM) or white matter (WM) differences and permit neurological disease detection and monitoring.The aims of the study were to quantify T1, T2 and PD values in all cortical gray matter regions for a group of healthy volunteers scanned at 1.5 T and to cluster regions showing statistically distinguishable tissue characteristics.Using a combination of spoiled gradient recalled echo (SPGR) and fast spin echo (FSE) sequences, 3D T1, T2 and PD of the brain were measured at 1.5 T for twenty healthy young volunteers. Cortical GM volumes of interest (VOIs) were identified by transforming 56 labels from an atlas onto each subject volumes: 8 frontal, 5 parietal, 6 occipital and 9 temporal on both the left and right sides. T1, T2 and PD measurements within these anatomical regions were quantified and reported here.Correspondence analysis (CA) and hierarchical clustering (HC) were combined and applied to averaged T1, T2 and PD values within each VOI in order to identify groups of anatomical structures that are related statistically. Interestingly, except for one structure, all VOIs were grouped with left-right symmetry and showed an interesting pattern: the four lobes (frontal, occipital, parietal and temporal) were roughly clustered and the precentral and postcentral gyri were merged together. Our study shows that CA and HC analysis of MRI relaxation parameters and proton density can be used for cortical clustering of atlas-defined cortical regions.

Child neglect followed by marked thymic involution and fatal systemic pseudomonas infection

The case of a 9-month-old baby girl who failed to develop normally due to nutritional neglect and secondary immunodeficiency characterized by marked thymic involution is reported. The child died of systemic Pseudomonas aeruginosa (P. aeruginosa) infection manifested in pneumonia, lung abscesses, bacterial endocarditis and ecthyma gangrenosum. At autopsy the child was 64 cm in height (normal for a 4- to 5-month-old child) and 5.1 kg in weight (normal for a 2- to 3-month-old child). Multiple gangrenous ecthymas, consisting of deep ulcers, induration and inflammation, were observed in the skin over the entire body. The lungs showed hemorrhagic pneumonia, multiple lung abscesses, and necrotizing arteritis in the abscesses and surrounding areas. The thymus weighed 2.3 g and showed marked involution. Histological examination showed so-called nutritional thymectomy characterized by severe cortical atrophy and clustering, cystic dilation and amorphous changes of the Hassall's corpuscles. In the heart, dark brown verrucae were present at the attachment sites of the tendinous cords of the papillary muscle in the anterior and posterior cusps of the mitral valve, suggesting infectious endocarditis. Bacteriological examination demonstrated P. aeruginosa in the ecthymas, lung abscesses and blood. As primary immunodeficiency was considered unlikely, immunodeficiency secondary to thymic involution following malnutrition seemed to have led to a fatal systemic infection with P. aeruginosa, whose virulence is generally weak. This suggests a close association of the development of such infection and immunodeficiency with child neglect.