The bacterial division apparatus catalyses the synthesis and remodelling of septal peptidoglycan (sPG) to build the cell wall layer that fortifies the daughter cell poles. Understanding of this essential process has been limited by the lack of native three-dimensional views of developing septa. Here, we apply state-of-the-art cryogenic electron tomography (cryo-ET) and fluorescence microscopy to visualize the division site architecture and sPG biogenesis dynamics of the Gram-negative bacterium Escherichia coli. We identify a wedge-like sPG structure that fortifies the ingrowing septum. Experiments with strains defective in sPG biogenesis revealed that the septal architecture and mode of division can be modified to more closely resemble that of other Gram-negative (Caulobacter crescentus) or Gram-positive (Staphylococcus aureus) bacteria, suggesting that a conserved mechanism underlies the formation of different septal morphologies. Finally, analysis of mutants impaired in amidase activation (ΔenvC ΔnlpD) showed that cell wall remodelling affects the placement and stability of the cytokinetic ring. Taken together, our results support a model in which competition between the cell elongation and division machineries determines the shape of cell constrictions and the poles they form. They also highlight how the activity of the division system can be modulated to help generate the diverse array of shapes observed in the bacterial domain.

• MeSH
• Amidohydrolases MeSH
• Cell Wall MeSH
• Cell Division MeSH
• Escherichia coli * physiology   MeSH
• Peptidoglycan * MeSH
• Cell Shape MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Research Support, N.I.H., Extramural MeSH
• Names of Substances
• Amidohydrolases MeSH
• Peptidoglycan * MeSH

Plant cell morphogenesis involves concerted rearrangements of microtubules and actin microfilaments. We previously reported that FH1, the main Arabidopsis thaliana housekeeping Class I membrane-anchored formin, contributes to actin dynamics and microtubule stability in rhizodermis cells. Here we examine the effects of mutations affecting FH1 (At3g25500) on cell morphogenesis and above-ground organ development in seedlings, as well as on cytoskeletal organization and dynamics, using a combination of confocal and variable angle epifluorescence microscopy with a pharmacological approach. Homozygous fh1 mutants exhibited cotyledon epinasty and had larger cotyledon pavement cells with more pronounced lobes than the wild type. The pavement cell shape alterations were enhanced by expression of the fluorescent microtubule marker GFP-microtubule-associated protein 4 (MAP4). Mutant cotyledon pavement cells exhibited reduced density and increased stability of microfilament bundles, as well as enhanced dynamics of microtubules. Analogous results were also obtained upon treatments with the formin inhibitor SMIFH2 (small molecule inhibitor of formin homology 2 domains). Pavement cell shape in wild-type (wt) and fh1 plants in some situations exhibited a differential response towards anti-cytoskeletal drugs, especially the microtubule disruptor oryzalin. Our observations indicate that FH1 participates in the control of microtubule dynamics, possibly via its effects on actin, subsequently influencing cell morphogenesis and macroscopic organ development.

• Keywords
• Arabidopsis thaliana, Confocal microscopy, Cotyledon pavement cells, Cytoskeleton, Formin, Variable angle epifluorescence microscopy,
• MeSH
• Actins metabolism   MeSH
• Arabidopsis cytology   drug effects   metabolism   MeSH
• Biomarkers metabolism   MeSH
• Models, Biological MeSH
• Cytoskeleton drug effects   metabolism   MeSH
• Fluorescence MeSH
• Formins MeSH
• Clathrin metabolism   MeSH
• Cotyledon drug effects   metabolism   MeSH
• Membrane Proteins metabolism   MeSH
• Actin Cytoskeleton drug effects   metabolism   MeSH
• Microtubules drug effects   metabolism   MeSH
• Mutation genetics   MeSH
• Arabidopsis Proteins metabolism   MeSH
• Seedlings drug effects   growth & development   metabolism   MeSH
• Thiones pharmacology   MeSH
• Cell Shape * drug effects   MeSH
• Uracil analogs & derivatives   pharmacology   MeSH
• Green Fluorescent Proteins metabolism   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• AFH1 protein, Arabidopsis MeSH Browser
• Actins MeSH
• Biomarkers MeSH
• Formins MeSH
• Clathrin MeSH
• Membrane Proteins MeSH
• Arabidopsis Proteins MeSH
• SMIFH2 compound MeSH Browser
• Thiones MeSH
• Uracil MeSH
• Green Fluorescent Proteins MeSH

Data-driven cell tracking and segmentation methods in biomedical imaging require diverse and information-rich training data. In cases where the number of training samples is limited, synthetic computer-generated data sets can be used to improve these methods. This requires the synthesis of cell shapes as well as corresponding microscopy images using generative models. To synthesize realistic living cell shapes, the shape representation used by the generative model should be able to accurately represent fine details and changes in topology, which are common in cells. These requirements are not met by 3D voxel masks, which are restricted in resolution, and polygon meshes, which do not easily model processes like cell growth and mitosis. In this work, we propose to represent living cell shapes as level sets of signed distance functions (SDFs) which are estimated by neural networks. We optimize a fully-connected neural network to provide an implicit representation of the SDF value at any point in a 3D+time domain, conditioned on a learned latent code that is disentangled from the rotation of the cell shape. We demonstrate the effectiveness of this approach on cells that exhibit rapid deformations (Platynereis dumerilii), cells that grow and divide (C. elegans), and cells that have growing and branching filopodial protrusions (A549 human lung carcinoma cells). A quantitative evaluation using shape features and Dice similarity coefficients of real and synthetic cell shapes shows that our model can generate topologically plausible complex cell shapes in 3D+time with high similarity to real living cell shapes. Finally, we show how microscopy images of living cells that correspond to our generated cell shapes can be synthesized using an image-to-image model.

• Keywords
• Cell shape modeling, Generative model, Implicit neural representation, Neural network,
• MeSH
• Caenorhabditis elegans * MeSH
• Humans MeSH
• Mitosis MeSH
• Lung Neoplasms * MeSH
• Neural Networks, Computer MeSH
• Image Processing, Computer-Assisted methods   MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH

We present a fast and robust approach to tracking the evolving shape of whole fluorescent cells in time-lapse series. The proposed tracking scheme involves two steps. First, coherence-enhancing diffusion filtering is applied on each frame to reduce the amount of noise and enhance flow-like structures. Second, the cell boundaries are detected by minimizing the Chan-Vese model in the fast level set-like and graph cut frameworks. To allow simultaneous tracking of multiple cells over time, both frameworks have been integrated with a topological prior exploiting the object indication function. The potential of the proposed tracking scheme and the advantages and disadvantages of both frameworks are demonstrated on 2-D and 3-D time-lapse series of rat adipose-derived mesenchymal stem cells and human lung squamous cell carcinoma cells, respectively.

• MeSH
• Cell Nucleus chemistry   MeSH
• Cell Tracking methods   MeSH
• Microscopy, Fluorescence methods   MeSH
• Rats MeSH
• Humans MeSH
• Mesenchymal Stem Cells cytology   MeSH
• Cell Line, Tumor MeSH
• Image Processing, Computer-Assisted methods   MeSH
• Cell Shape physiology   MeSH
• Animals MeSH
• Check Tag
• Rats MeSH
• Humans MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH

Overtly self-reactive T cells are removed during thymic selection. However, it has been recently established that T cell self-reactivity promotes protective immune responses. Apparently, the level of self-reactivity of mature T cells must be tightly balanced. Our mathematical model and experimental data show that the dynamic regulation of CD4- and CD8-LCK coupling establish the self-reactivity of the peripheral T cell pool. The stoichiometry of the interaction between CD8 and LCK, but not between CD4 and LCK, substantially increases upon T cell maturation. As a result, peripheral CD8+ T cells are more self-reactive than CD4+ T cells. The different levels of self-reactivity of mature CD8+ and CD4+ T cells likely reflect the unique roles of these subsets in immunity. These results indicate that the evolutionary selection pressure tuned the CD4-LCK and CD8-LCK stoichiometries, as they represent the unique parts of the proximal T cell receptor (TCR) signaling pathway, which differ between CD4+ and CD8+ T cells.

• Keywords
• CD4, CD8, LCK, T cell, TCR, evolution of the immune system, lymphocyte, self-reactivity, signaling, thymus,
• MeSH
• Antigens metabolism   MeSH
• Cell Differentiation MeSH
• CD4-Positive T-Lymphocytes cytology   metabolism   MeSH
• CD8-Positive T-Lymphocytes cytology   metabolism   MeSH
• Homeostasis MeSH
• Mice, Inbred C57BL MeSH
• Signal Transduction MeSH
• Lymphocyte Specific Protein Tyrosine Kinase p56(lck) metabolism   MeSH
• Protein Binding MeSH
• Animals MeSH
• Check Tag
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Antigens MeSH
• Lymphocyte Specific Protein Tyrosine Kinase p56(lck) MeSH

Nanoparticle-cell interactions begin with the cellular uptake of the nanoparticles, a process that eventually determines their cellular fate. In the present work, we show that the morphological features of nanodiamonds (NDs) affect both the anchoring and internalization stages of their endocytosis. While a prickly ND (with sharp edges/corners) has no trouble of anchoring onto the plasma membrane, it suffers from difficult internalization afterwards. In comparison, the internalization of a round ND (obtained by selective etching of the prickly ND) is not limited by its lower anchoring amount and presents a much higher endocytosis amount. Molecular dynamics simulation and continuum modelling results suggest that the observed difference in the anchoring of round and prickly NDs likely results from the reduced contact surface area with the cell membrane of the former, while the energy penalty associated with membrane curvature generation, which is lower for a round ND, may explain its higher probability of the subsequent internalization.

• MeSH
• Models, Biological MeSH
• Cell Membrane chemistry   MeSH
• Hep G2 Cells MeSH
• Endocytosis MeSH
• HeLa Cells MeSH
• Humans MeSH
• Nanodiamonds chemistry   MeSH
• Molecular Dynamics Simulation MeSH
• Cell Survival MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Nanodiamonds MeSH

The CLAVATA pathway is a key regulator of stem cell function in the multicellular shoot tips of Arabidopsis, where it acts via the WUSCHEL transcription factor to modulate hormone homeostasis. Broad-scale evolutionary comparisons have shown that CLAVATA is a conserved regulator of land plant stem cell function, but CLAVATA acts independently of WUSCHEL-like (WOX) proteins in bryophytes. The relationship between CLAVATA, hormone homeostasis and the evolution of land plant stem cell functions is unknown. Here we show that in the moss, Physcomitrella (Physcomitrium patens), CLAVATA affects stem cell activity by modulating hormone homeostasis. CLAVATA pathway genes are expressed in the tip cells of filamentous tissues, regulating cell identity, filament branching, plant spread and auxin synthesis. The receptor-like kinase PpRPK2 plays the major role, and Pprpk2 mutants have abnormal responses to cytokinin, auxin and auxin transport inhibition, and show reduced expression of PIN auxin transporters. We propose a model whereby PpRPK2 modulates auxin gradients in filaments to determine stem cell identity and overall plant form. Our data indicate that CLAVATA-mediated auxin homeostasis is a fundamental property of plant stem cell function, probably exhibited by the last shared common ancestor of land plants.

• Keywords
• CLAVATA, CLV-WUS, evo-devo, moss filament identity, physcomitrella, plant stem cell,
• MeSH
• Bryophyta * metabolism   MeSH
• Homeostasis MeSH
• Stem Cells metabolism   MeSH
• Indoleacetic Acids metabolism   MeSH
• Bryopsida * genetics   metabolism   MeSH
• Arabidopsis Proteins * genetics   metabolism   MeSH
• Gene Expression Regulation, Plant MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Indoleacetic Acids MeSH
• Arabidopsis Proteins * MeSH

To develop materials for drug delivery and tissue engineering and to study their efficiency with respect to ossification, it is necessary to apply physicochemical and biological analyses. The major challenge is labor-intensive data mining during synthesis and the reproducibility of the obtained data. In this work, we investigated the influence of time and temperature on the reaction yield, the reaction rate, and the size, shape, and phase of the obtained product in the completely controllable synthesis of calcium carbonate. We show that calcium carbonate particles can be synthesized in large quantities, i.e., in gram quantities, which is a substantial advantage over previously reported synthesis methods. We demonstrated that the presence of vaterite particles can dramatically stimulate hydroxyapatite (HA) production by providing the continued release of the main HA component - calcium ions - depending on the following particle parameters: size, shape, and phase. To understand the key parameters influencing the efficiency of HA production by cells, we created a predictive model by means of principal component analysis. We found that smaller particles in the vaterite state are best suited for HA growth (HA growth was 8 times greater than that in the control). We also found that the reported dependence of cell adhesion on colloidal particles can be extended to other types of particles that contain calcium ions.

• MeSH
• 3T3 Cells MeSH
• Hydroxyapatites chemistry   metabolism   MeSH
• Drug Delivery Systems MeSH
• Mice MeSH
• Osteoblasts drug effects   metabolism   MeSH
• Tissue Engineering MeSH
• Calcium Carbonate chemical synthesis   chemistry   MeSH
• Cell Survival drug effects   MeSH
• Animals MeSH
• Check Tag
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Hydroxyapatites MeSH
• Calcium Carbonate MeSH

A model of biological effects of ionizing particles, especially of protons and other ions, is proposed. The model is based on distinguishing the single-particle and collective effects of the underlying radiobiological mechanism. The probabilities of individual particles causing severe damage to DNA, their synergetic or saturation combinations, and the effect of the cellular repair system are taken into account. The model enables one to describe linear, parabolic and more complex curves, including those exhibiting low-dose hypersensitivity phenomena, in a systematic way. Global shape as well as detailed structure of survival curves might be represented, which is crucial if different fractionation schemes in radiotherapy should be assessed precisely. Experimental cell-survival data for inactivation of V79 cells by low-energy protons have been analysed and corresponding detailed characteristics of the inactivation mechanism have been derived for this case.

• MeSH
• Apoptosis radiation effects   MeSH
• Models, Biological * MeSH
• Cell Line MeSH
• Cricetulus MeSH
• Radiation Dosage MeSH
• DNA radiation effects   MeSH
• Fibroblasts physiology   radiation effects   MeSH
• Radiation, Ionizing * MeSH
• Cricetinae MeSH
• Computer Simulation MeSH
• DNA Damage * MeSH
• Models, Statistical MeSH
• Cell Survival radiation effects   MeSH
• Dose-Response Relationship, Radiation MeSH
• Animals MeSH
• Check Tag
• Cricetinae MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Comparative Study MeSH
• Names of Substances
• DNA MeSH

Intracellular and extracellular mechanical forces play a crucial role during tissue growth, modulating nuclear shape and function and resulting in complex collective cell behaviour. However, the mechanistic understanding of how the orientation, shape, symmetry and homogeneity of cells are affected by environmental geometry is still lacking. Here we investigate cooperative cell behaviour and patterns under geometric constraints created by topographically patterned substrates. We show how cells cooperatively adopt their geometry, shape, positioning of the nucleus and subsequent proliferation activity. Our findings indicate that geometric constraints induce significant squeezing of cells and nuclei, cytoskeleton reorganization, drastic condensation of chromatin resulting in a change in the cell proliferation rate and the anisotropic growth of cultures. Altogether, this work not only demonstrates complex non-trivial collective cellular responses to geometrical constraints but also provides a tentative explanation of the observed cell culture patterns grown on different topographically patterned substrates. These findings provide important fundamental knowledge, which could serve as a basis for better controlled tissue growth and cell-engineering applications.

• MeSH
• Models, Biological * MeSH
• Cell Nucleus physiology   ultrastructure   MeSH
• Mechanotransduction, Cellular physiology   MeSH
• Hep G2 Cells MeSH
• Humans MeSH
• Cell Communication physiology   MeSH
• Computer Simulation MeSH
• Cell Proliferation physiology   MeSH
• Cell Size * MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH