Cell–cell communication in Arabidopsis early embryogenesis

The basic body plan of the adult plant is established during embryogenesis, resulting in the juvenile form of the seedling. Arabidopsis embryogenesis is distinguished by a highly regular pattern of cell divisions. Some of these divisions are asymmetric, generating daughter cells with different fates. However, their subsequent differentiation might still depend on cell–cell communication to be fully accomplished or maintained. In some cases, cell fate specification solely depends on cell–cell communication that in general plays an important role in the generation of positional information within the embryo. Although auxin-dependent signalling has received much attention, other ways of cell–cell communication have also been demonstrated or suggested. This review focuses on aspects of pattern formation and cell–cell communication during Arabidopsis embryogenesis up to the mid-globular stage of development.     

Does efficiency sensing unify diffusion and quorum sensing?

Quorum sensing faces evolutionary problems from non-producing or over-producing cheaters. Such problems are circumvented in diffusion sensing, an alternative explanation for quorum sensing. However, both explanations face the problems of signalling in complex environments such as the rhizosphere where, for example, the spatial distribution of cells can be more important for sensing than cell density, which we show by mathematical modelling. We argue that these conflicting concepts can be unified by a new hypothesis, efficiency sensing, and that some of the problems associated with signalling in complex environments, as well as the problem of maintaining honesty in signalling, can be avoided when the signalling cells grow in microcolonies.     

Is quorum sensing a side effect of diffusion sensing?

Many bacteria appear to communicate by releasing and sensing autoinducer molecules, which are believed to function primarily as sensors of population density. However, this quorum-sensing hypothesis rests on very weak foundations, as neither the need for group action nor the selective conditions required for its evolution have been demonstrated. Here, I argue for a more direct function of autoinducer secretion and response - the ability to determine whether secreted molecules rapidly move away from the cell. This diffusion sensing allows cells to regulate secretion of degradative enzymes and other effectors to minimize losses owing to extracellular diffusion and mixing.     

Cell–cell contact and signaling in the muscle stem cell niche

Muscle stem cells (also called satellite cells or SCs) rely on their local niche for regulatory signals during homeostasis and regeneration. While a number of cell types communicate indirectly through secreted factors, here we focus on the significance of direct contact between SCs and their neighbors. During quiescence, SCs reside under a basal lamina and receive quiescence-promoting signals from their adjacent skeletal myofibers. Upon injury, the composition of the niche changes substantially, enabling the formation of new contacts that mediate proliferation, self-renewal, and differentiation. In this review, we summarize the latest work in understanding cell–cell contact within the satellite cell niche and highlight areas of open questions for future studies.     

Deterministic and stochastic modelling of endosome escape by Staphylococcus aureus: “quorum” sensing by a single bacterium

Deterministic and stochastic models describing quorum sensing by Staphylococcus aureus within an endosome, and the subsequent escape via the production of virulence factors, are developed and analysed. Particular attention is given to a biologically-relevant asymptotic limit of the problem, for which the solutions, including the endosome escape time, can be explicitly characterised in terms of the model parameters.     

Exosomes as new vesicular lipid transporters involved in cell–cell communication and various pathophysiologies

Exosomes are nanovesicles that have emerged as a new intercellular communication system between an intracellular compartment of a donor cell towards the periphery or an internal compartment of a recipient cell. The bioactivity of exosomes resides not only in their protein and RNA contents but also in their lipidic molecules. Exosomes display original lipids organized in a bilayer membrane and along with the lipid carriers such as fatty acid binding proteins that they contain, exosomes transport bioactive lipids. Exosomes can vectorize lipids such as eicosanoids, fatty acids, and cholesterol, and their lipid composition can be modified by in-vitro manipulation. They also contain lipid related enzymes so that they can constitute an autonomous unit of production of various bioactive lipids. Exosomes can circulate between proximal or distal cells and their fate can be regulated in part by lipidic molecules. Compared to their parental cells, exosomes are enriched in cholesterol and sphingomyelin and their accumulation in cells might modulate recipient cell homeostasis. Exosome release from cells appears to be a general biological process. They have been reported in all biological fluids from which they can be recovered and can be monitors of specific pathophysiological situations. Thus, the lipid content of circulating exosomes could be useful biomarkers of lipid related diseases. Since the first lipid analysis of exosomes ten years ago detailed knowledge of exosomal lipids has accumulated. The role of lipids in exosome fate and bioactivity and how they constitute an additional lipid transport system are considered in this review.     

Understanding LuxS-based quorum sensing and its inhibition – molecular dynamics simulation study

Molecular dynamics simulations were successfully applied to LuxS protein and its protein–ligand complex using the newly developed force field parameters for the iron containing active site. To the best of our knowledge, this was the first attempt to develop force field parameters for the iron containing active site of the LuxS protein. From the simulations, catalytically important amino acid residues were identified which were found to stabilise the ligand. Two residues Glu57 and Asp77 were involved in polar interactions while the protein region in the range between amino acid residue 125 and 131 were predicted to facilitate the entry of ligand to the active site. Other residues like Arg65, Asp77, Ile78 and Ser79 were also recognised as ligand stabilising factors deduced from the simulation. These results were also found to be in good agreement with earlier studies and thus demonstrated the successful application of MD simulations to the LuxS protein. Moreover, the simulation data were expected to be considered for the development of rational approaches in order to identify new LuxS-based quorum sensing antagonists for the treatment of pathologies caused by resistant bacteria.     

Cell–cell communications and molecular mechanisms in plant sexual reproduction

Sexual reproduction is achieved by precise interactions between male and female reproductive organs. In plant fertilization, sperm cells are carried to ovules by pollen tubes. Signals from the pistil are involved in elongation and control of the direction of the pollen tube. Genetic, reverse genetic, and cell biological analyses using model plants have identified various factors related to the regulation of pollen tube growth and guidance. In this review, I summarize the mechanisms and molecules controlling pollen tube growth to the ovule, micropylar guidance, reception of the guidance signal in the pollen tube, rupture of the pollen tube to release sperm cells, and cessation of the tube guidance signal. I also briefly introduce various techniques used to analyze pollen tube guidance in vitro.     

Cell–cell Signaling in the Neurovascular Unit

Historically, the neuron has been the conceptual focus for almost all of neuroscience research. In recent years, however, the concept of the neurovascular unit has emerged as a new paradigm for investigating both physiology and pathology in the CNS. This concept proposes that a purely neurocentric focus is not sufficient, and emphasizes that all cell types in the brain including neuronal, glial and vascular components, must be examined in an integrated context. Cell–cell signaling and coupling between these different compartments form the basis for normal function. Disordered signaling and perturbed coupling form the basis for dysfunction and disease. In this mini-review, we will survey four examples of this phenomenon: hemodynamic neurovascular coupling linking blood flow to brain activity; cellular communications that evoke the blood–brain barrier phenotype; parallel systems that underlie both neurogenesis and angiogenesis in the CNS; and finally, the potential exchange of trophic factors that may link neuronal, glial and vascular homeostasis. Special issue in honor of Naren Banik.     

Angiotensin (1–7) re-establishes heart cell communication previously impaired by cell swelling: Implications for myocardial ischemia

The influence of hypertonic solution on dye coupling was investigated in cell pairs isolated from the left ventricle of adult Sprague Dawley rats.The hypertonic solution together with Lucifer Yellow CH, were dialyzed into one cell of the pair using the whole cell clamp tecnique, and the diffusion of dye in the dialyzed as well as in non-dialyzed cell, was followed by measuring the intensity of fluorescence in both cells as a function of time.The results indicated that: (1) Lucifer Yellow CH dialyzed into one cell of the pair diffuses easily into the nondialyzed cell through gap junctions; (2) the intracellular dialysis of an hypertonic solution into one cell of the pair, increases the area of the dialyzed cell and reduced the area of the non-dialyzed cell suggesting intercellular movement of water; (3) the hypertonic solution dialyzed into one cell of the pair abolished the dye coupling; (4) the gap junction permeability (Pj) estimated before and after administration of hypertonic solution showed an appreciably decrease of Pj; (5) angiotensin (1–7) (Ang (1–7) (10–9 M) administered to the bath re-established the dye coupling abolished by hypertonic solution and reduced the cell area; (6) the effect of Ang (1–7) was related to the activation of Mas receptor and was dependent on the activation of PKA. Conclusions: the reestablishment of dye coupling elicited by Ang (1–7) seen in cell pairs dialyzed with hypertonic solution, might indicate that under similar conditions like that seen during myocardial ischemia, the peptide might be of benefit preventing the impairment of cell communication and impulse propagation associated with cardiac reentrant arrhytmias.