Supracellular Level Research Articles

Analysis of mRNA Subcellular Distribution in Collective Cell Migration.

The movement of groups of cells by collective cell migration requires division of labor between group members. Therefore, distinct cell identities, unique cell behaviors, and specific cellular roles are acquired by cells undergoing collective movement. A key driving force behind the acquisition of discrete cell states is the precise control of where, when, and how genes are expressed, both at the subcellular and supracellular level. Unraveling the mechanisms underpinning the spatiotemporal control of gene expression in collective cell migration requires not only suitable experimental models but also high-resolution imaging of messenger RNA and protein localization during this process. In recent times, the highly stereotyped growth of new blood vessels by sprouting angiogenesis has become a paradigm for understanding collective cell migration, and consequently this has led to the development of numerous user-friendly in vitro models of angiogenesis. In parallel, single-molecule fluorescent in situ hybridization (smFISH) has come to the fore as a powerful technique that allows quantification of both RNA number and RNA spatial distribution in cells and tissues. Moreover, smFISH can be combined with immunofluorescence to understand the precise interrelationship between RNA and protein distribution. Here, we describe methods for use of smFISH and immunofluorescence microscopy in in vitro angiogenesis models to enable the investigation of RNA and protein expression and localization during endothelial collective cell migration.

Genotype-dependent changes of cell wall composition influence physiological traits of a long and a non-long shelf-life tomato genotypes under distinct water regimes.

Water shortage strongly affects plants' physiological performance. Since tomato (Solanum lycopersicum) non-long shelf-life (nLSL) and long shelf-life (LSL) genotypes differently face water deprivation, we subjected a nLSL and a LSL genotype to four treatments: control (well watering), short-term water deficit stress at 40% field capacity (FC) (ST 40% FC), short-term water deficit stress at 30% FC (ST 30% FC), and short-term water deficit stress at 30% FC followed by recovery (ST 30% FC-Rec). Treatments promoted genotype-dependent elastic adjustments accompanied by distinct photosynthetic responses. While the nLSL genotype largely modified mesophyll conductance (gm ) across treatments, it was kept within a narrow range in the LSL genotype. However, similar gm values were achieved under ST 30% FC conditions. Particularly, modifications in the relative abundance of cell wall components and in sub-cellular anatomic parameters such as the chloroplast surface area exposed to intercellular air space per leaf area (Sc /S) and the cell wall thickness (Tcw ) regulated gm in the LSL genotype. Instead, only changes in foliar structure at the supra-cellular level influenced gm in the nLSL genotype. Even though further experiments testing a larger range of genotypes and treatments would be valuable to support our conclusions, we show that even genotypes of the same species can present different elastic, anatomical, and cell wall composition-mediated mechanisms to regulate gm when subjected to distinct water regimes.

Anxiety and depression: A matter of stiffness?

Cells react to stress by the universal responses of “fluidization” or “reinforcement” (stiffening) of the cytoplasm, through dramatic re-arrangements of the cytoskeleton. Here it is suggested that, at a supracellular level, the brain exhibits such a fundamental behavior as part of its complex response to stress: it is hypothesized that the soft gel formed by brain cell cytoskeletons and the surrounding extracellular matrix (the “cytoskeletons-matrix system”) undergoes transitions either to sol (fluidization) or stiff gel (reinforcement) as a very fundamental and evolutionarily conserved brain response to stress, alongside more sophisticated neural pathways. Sol state corresponds to increased cell activity (a sort of “fight or flight” response), whereas stiff gel state corresponds to inactivity (an “immobility” strategy).Psychological stress, through simple stress signals such as pH changes, would lead to an initial tissue fluidization in key regions of the brain, followed, if the stress stimuli persist, by reinforcement (slow formation of actomyosin stress fibers and matrix stiffening).It is also hypothesized that the cytoskeletons-matrix system is one of the biological correlates of so-called “background feelings”, i.e conscious feelings built on inner chemical-physical states of the body. Optimal dynamics of the cytoskeletons-matrix system would contribute to a core feeling of well-being, while shifts towards fluidization (activation) or stiffening (inactivation) would contribute to background feelings at the basis of anxiety and stress-induced depression, respectively.It is suggested that the cytoskeletons-matrix system behaves as a “self-organized critical system”, anxiety and depression arising whenever the system is driven too far from the optimal critical point.Finally, some application hints from the proposed ideas are given.

Control of Cell Migration Using Optogenetics.

Optogenetics uses light to manipulate protein localization or activity from subcellular to supra-cellular level with unprecedented spatiotemporal resolution. We used it to control the activity of the Cdc42 Rho GTPase, a major regulator of actin polymerization and cell polarity. In this chapter, we describe how to trigger and guide cell migration using optogenetics as a way to mimic EMT in an artificial yet highly controllable fashion.

Synaptic Communication Engineering for Future Cognitive Brain–Machine Interfaces

Disease-affected nervous systems exhibit anatomical or physiological impairments that degrade processing, transfer, storage, and retrieval of neural information, leading to physical or intellectual disabilities. Brain implants may potentially promote clinical means for detecting and treating neurological symptoms by establishing direct communication between the nervous and artificial systems. Current technology can modify the neural function at the supracellular level as in Parkinson's disease, epilepsy, and depression. However, recent advances in nanotechnology, nanomaterials, and molecular communications have the potential to enable brain implants to preserve the neural function at the subcellular level, which could increase effectiveness, decrease energy consumption, and make the leadless devices chargeable from outside the body or by utilizing the body's own energy sources. In this paper, we focus on understanding the principles of elemental processes in synapses to enable diagnosis and treatment of brain diseases with pathological conditions using biomimetic synaptically interactive brain-machine interfaces (BMIs). First, we provide an overview of the synaptic communication system, followed by an outline of brain diseases that promote dysfunction in the synaptic communication system. Then, we discuss the technologies for brain implants and propose future directions for the design and fabrication of cognitive BMIs. The overarching goal of this paper is to summarize the status of engineering research at the interface between the technology and the nervous system and direct the ongoing research toward the point where synaptically interactive BMIs can be embedded in the nervous system.

Functional Epithelium Remodeling in Response to Applied Stress under In Vitro Conditions.

Mathematical modeling is often used in tissue engineering in order to overcome one of its major challenges: transformation of complex biological and rheological behaviors of cells and tissue in a mathematically predictive and physically manipulative engineering process. The successive accomplishment of this task will greatly help in quantifying and optimizing clinical application of the tissue engineering products. One of the problems emerging in this area is the relation between resting and migrating cell groups, as well as between different configurations of migrating cells and viscoelasticity. A deeper comprehension of the relation between various configurations of migrating cells and viscoelasticity at the supracellular level represents the prerequisite for optimization of the performance of the artificial epithelium. Since resting and migrating cell groups have a considerable difference in stiffness, a change in their mutual volume ratio and distribution may affect the viscoelasticity of multicellular surfaces. If those cell groups are treated as different phases, then an analogous model may be applied to represent such systems. In this work, a two-step Eyring model is developed in order to demonstrate the main mechanical and biochemical factors that influence configurations of migrating cells. This model could be also used for considering the long-time cell rearrangement under various types of applied stress. The results of this theoretical analysis point out the cause-consequence relationship between the configuration of migrating cells and rheological behavior of multicellular surfaces. Configuration of migrating cells is influenced by mechanical and biochemical perturbations, difficult to measure experimentally, which lead to uncorrelated motility. Uncorrelated motility results in (1) decrease of the volume fraction of migrating cells, (2) change of their configuration, and (3) softening of multicellular surfaces.

Confinement-Induced Transition between Wavelike Collective Cell Migration Modes.

The structural and functional organization of biological tissues relies on the intricate interplay between chemical and mechanical signaling. Whereas the role of constant and transient mechanical perturbations is generally accepted, several studies recently highlighted the existence of long-range mechanical excitations (i.e., waves) at the supracellular level. Here, we confine epithelial cell monolayers to quasi-one-dimensional geometries, to force the establishment of tissue-level waves of well-defined wavelength and period. Numerical simulations based on a self-propelled Voronoi model reproduce the observed waves and exhibit a phase transition between a global and a multinodal wave, controlled by the confinement size. We confirm experimentally the existence of such a phase transition, and show that wavelength and period are independent of the confinement length. Together, these results demonstrate the intrinsic origin of tissue oscillations, which could provide cells with a mechanism to accurately measure distances at the supracellular level.

A hypothesis concerning callose

ABSTRACTBackground Concept: Certain proteins and the glucose monomer have spacing of their carbonyl oxygen atoms that match the spacing of the oxygen atoms of hexagonal ice. This opens the possibility that a sequence of linked glucose residues may have a sequence of equally spaced carbonyl oxygen atoms. Hypothesis: Callose In plants is a duality consisting of the callose itself and a layer of ordered water whose oxygen atoms are hydrogen bonded to the carbonyl oxygen atoms in the callose. The atomic basis of the hypothesis is that the 1–3 linkage between glucose residues in callose results in equally spaced carbonyl oxygen atoms within and between residues. Properties of Callose/Ordered Water: The physical properties of the duality are the properties of callose itself: 1) it is immobile, 2) it can be created and dissolved, 3) it can exist at a submicrometer to micrometers space scale. The electrical properties of ordered water in a botanical platform are not known at the present time. They can be derived only from limited data in non biological platforms and inferences from the electrical properties of ice. These properties are 1) proton movement is governed by the Grotthuss mechanism, 2) there is insignificant movement of non-protonic ions and larger molecules through the ordered water, 3) proton movement is isotropic. Proposed Functionality of Callose/Ordered Water: Known locations of callose were examined theoretically to determine the functionality of a callose/ordered water duality. These locations were sieve plate pores, plasmodesmata and pollen tubes, stomatal guard cells, companion cell/sieve tube complex and micro and megasporocytes. Protonic Circuits: In a botanical context, protonic circuits at a single cell and supracellular level take the form of a proton microloop wherein callose/ordered water is one component in the loop. These circuits use both the enhanced proton mobility and the ion blocking ability of ordered water.

WHAT ROLES FOR TRACK-STRUCTURE AND MICRODOSIMETRY IN THE ERA OF -omics AND SYSTEMS BIOLOGY?

Ionizing radiation is a peculiar perturbation when it comes to damage to biological systems: it proceeds through discrete energy depositions, over a short temporal scale and a spatial scale critical for subcellular targets as DNA, whose damage complexity determines the outcome of the exposure. This lies at the basis of the success of track structure (and nanodosimetry) and microdosimetry in radiation biology. However, such reductionist approaches cannot account for the complex network of interactions regulating the overall response of the system to radiation, particularly when effects are manifest at the supracellular level and involve long times. Systems radiation biology is increasingly gaining ground, but the gap between reductionist and holistic approaches is becoming larger. This paper presents considerations on what roles track structure and microdosimetry can have in the attempt to fill this gap, and on how they can be further exploited to interpret radiobiological data and inform systemic approaches.

Successive relaxation cycles during long-time cell aggregate rounding after uni-axial compression.

The mean features of cell surface rearrangement during cell aggregate rounding after uni-axial compression between parallel plates are considered. This is based on long-time rheological modeling approaches in order to shed further light on collective cell migration. Many aspects of cell migration at the supra-cellular level, such as the coordination between surrounding migrating cell groups that leads to uncorrelated motility, have remained unclear. Aggregate shape changes during rounding are considered depending on the size and homogeneity of 2-D and 3-D cell aggregates. Cell aggregate shape changes that are taking place during successive relaxation cycles have various relaxation rates per cycle. Every relaxation rate is related to the corresponding cell migrating state. If most of the cells migrate per cycle, the relaxation rate is maximal. If most of the cells are in a resting state per cycle, the relaxation rate is nearing zero. If some cell groups migrate while the others, at the same time, stay in a resting state, the relaxation rate is lower than that obtained for the migrating cells. The relaxation rates per cycles are not random, but they have a tendency to gather around two or three values indicating an organized cell migrating pattern. Such behavior suggests that uncorrelated motility during collective cell migration in one cycle induces a decrease of the relaxation rate in the next cycle caused by an accumulation of cells in the resting state. However, cells have the ability to overcome these perturbations and re-establish an ordered migrating trend in the next cycle. These perturbations of the cell migrating state are more pronounced for: (1) more mobile cells, (2) a heterogeneous cell population, and (3) a larger cell population under the same experimental conditions.

PIN2-like proteins may contribute to the regulation of morphogenetic processes during spermatogenesis in Chara vulgaris.

Key messagePIN2-like auxin transporters are expressed, preferentially in a polarized manner, in antheridial cells of freshwater green algaChara vulgaris, considered to be the closest relative of the present-day land plants.Chara vulgaris represents a group of advanced multicellular green algae that are considered as the closest relatives of the present-day land plants. A highly specialized structure of its male sex organs (antheridia) includes filaments consisting of generative cells, which after a series of synchronous divisions transform into mature sperm, and non-generative cells comprising outer shield cells, cylindrical manubria, and central complex of capitular cells from which antheridial filaments arise. Immunofluorescence observations indicate that PIN2-like proteins (PIN2-LPs), recognized by antibodies against PIN-FORMED2 (PIN2) auxin transporter in Arabidopsis thaliana, are expressed in both types of antheridial cells and, in most of them, preferentially accumulate in a polarized manner. The appearance of PIN2-LPs in germ-line cells is strictly confined to the proliferative period of spermatogenesis and their quantities increase steadily till antheridial filaments reach the 16-celled stage. An enhanced level of PIN2-LPs observed in the central cell walls separating two asynchronously developing parts of antheridial filaments (characterized by the plugged plasmodesmata) is correlated with an enhanced deposition of callose. Intense PIN2-LPs immunofluorescence maintained in the capitular cells and its altering polarity in manubria suggest a pivotal role of these cells in the regulation of auxin transport directionality during the whole time of antheridial ontogenesis. Immunohistochemical staining of IAA revealed a clear-cut correspondence between localization sites of auxins and PIN2-LPs. It seems probable then that a supplementary developmental mechanism has evolved in Chara, by which all antheridial elements may be integrated at the supra-cellular level via plasma membrane-targeted PIN2-LPs and auxin-mediated processes.

An added dimension to tumour TRAIL sensitivity.

Tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) is a member of the TNF cytokine family and a selective inducer of apoptosis in a range of tumour cells, but not in healthy normal, untransformed cells. It is expressed by natural killer cells and natural killer-T cells when they encounter malignantly transformed cells and it is a key effector molecule in tumour immune surveillance. TRAIL has 5 receptors, which is the highest receptor promiscuity in the TNF ligand family. It binds to death receptor 4 (DR4) or DR5 on the surface of target cells [1] and initiates a conformational change which promotes association of the receptors with FADD facilitating pro-caspase-8 and/or pro-caspase-10 recruitment which then activates effector caspases to execute cell death [2]. Signalling through DR4 and DR5 can also activate pro-inflammatory intracellular molecules such as MAPK, PKB and NF-κB and overexpression of DR4 or DR5 has been shown to stimulate the release of inflammatory cytokines [3]. However, TRAIL also has three regulatory receptors. Two of these, decoy receptor 1(DcR1) and DcR2 are membrane bound and the third regulatory receptor, osteoprotegerin is a secreted protein. DcRs regulate TRAIL-induced apoptosis by either sequestering TRAIL from the death receptors or by forming inactive, heteromeric DcR1/2–DR4/5 complexes [1]. Indeed, DcRs have been shown to be highly expressed in a number of tumour tissues such as acute myeloid leukaemia, prostate cancer and breast cancer and their expression is linked with poor prognosis [4]. However DcR expression in tumour cells does not correlate with TRAIL sensitivity and non-transformed cells do not require DcRs to be protected from TRAIL-induced apoptosis, suggesting that the in vivo role of the DcRs may be more complex than originally thought [5] The tumor-specific cytotoxicity of TRAIL has been exploited as a therapeutic strategy by utilizing recombinant versions of TRAIL and agonistic antibodies against DR4 and DR5 [6]. While recombinant soluble human TRAIL was highly potent against a broad range of tumours in vitro and in pre-clinical studies, in clinical trials TRAIL has failed to exhibit the same potency [6]. One of the major shortcomings of the preclinical models was the lack of assessment of the contribution of the tumour microenvironment (TME). The TME consists of various cell types, soluble factors and signals from the extracellular matrix, and is in a reciprocal interaction with the tumour cells. It is thus important to understand the interplay of different cell types in the tumour microenvironment and the effect of the factors they express and secrete on tumour growth, development and resistance to therapy. Figure 1 Cell autonomous and supracellular regulation of TRAIL-sensitivity by decoy receptor 1 (DcR1) and -2 The study by O'Leary and colleagues explored the hypothesis that DcRs exerted a ‘supracellular level control’ of TRAIL-sensitivity rather than simply regulating TRAIL resistance at a cell-autonomous level [7]. They firstly examined the expression of the decoy receptors in tumour cells, tumour stroma and in non-malignant, tumour adjacent tissues. Interestingly they found that DcR1 and DcR2 are commonly expressed in tissues but tissue stroma only express DcR1. To determine whether DcR-expressing stromal cells influence the TRAIL sensitivity of tumour cells sharing the same microenvironment they generated and characterized DcR-insensitive TRAIL mutants and used a combination of mathematical modelling, cell based assays and a stroma/tumour co-culture system allowing them to model the effect of DcRs expressed by adjacent stromal cells on DR4/5 activation in tumour cells. They found that stromal DcRs profoundly reduced TRAIL-induced DR4/DR5 activation and protected tumour cells against TRAIL. The authors confirmed this finding in a 3D mixed-cell type (stroma-tumour) spheroid tumour model. Interestingly they also observed that TNF increased surface expression of the DcRs in fibroblasts raising the possibility that an inflammatory environment may induce DcR expression and promote TRAIL resistance. This study clearly demonstrates that stromal DcRs in the tumour microenvironment can exert trans-cellular regulation affecting tumour cells and it highlights the importance of developing therapeutic TRAIL variants that can selectively activate the two death inducing TRAIL receptors but are not mopped up by the decoy receptors present on stromal tissues. Future studies will hopefully establish a feed forward signalling loop that drives overall tissue sensitivity in order to achieve tumour eradication.

Decoy receptors block TRAIL sensitivity at a supracellular level: the role of stromal cells in controlling tumour TRAIL sensitivity.

Tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) is a death ligand cytokine known for its cytotoxic activity against malignantly transformed cells. TRAIL induces cell death through binding to death receptors DR4 and DR5. The inhibitory decoy receptors (DcR1 and DcR2) co-expressed with death receptor 4 (DR4)/DR5 on the same cell can block the transmission of the apoptotic signal. Here, we show that DcRs also regulate TRAIL sensitivity at a supracellular level and thus represent a mechanism by which the microenvironment can diminish tumour TRAIL sensitivity. Mathematical modelling and layered or spheroid stroma-extracellular matrix-tumour cultures were used to model the tumour microenvironment. By engineering TRAIL to escape binding by DcRs, we found that DcRs do not only act in a cell-autonomous or cis-regulatory manner, but also exert trans-cellular regulation originating from stromal cells and affect tumour cells, highlighting the potent inhibitory effect of DcRs in the tumour tissue and the necessity of selective targeting of the two death-inducing TRAIL receptors to maximise efficacy.

Physiological mechanisms in plant growth models: do we need a supra‐cellular systems biology approach?

In the first part of this paper, we review the extent to which various types of plant growth models incorporate ecophysiological mechanisms. Many growth models have a central role for the process of photosynthesis; and often implicitly assume C-gain to be the rate-limiting step for biomass accumulation. We subsequently explore the extent to which this assumption actually holds and under what condition constraints on growth due to a limited sink strength are likely to occur. By using generalized dose-response curves for growth with respect to light and CO₂, models can be tested against a benchmark for their overall performance. In the final part, a call for a systems approach at the supra-cellular level is made. This will enable a better understanding of feedbacks and trade-offs acting on plant growth and its component processes. Mechanistic growth models form an indispensable element of such an approach and will, in the end, provide the link with the (sub-)cellular approaches that are yet developing. Improved insight will be gained if model output for the various physiological processes and morphological variables ('virtual profiling') is compared with measured correlation networks among these processes and variables. Two examples of these correlation networks are presented.

Metabolic and electrophysiological changes in the basal ganglia of transgenic Huntington's disease rats

Huntington's disease (HD) is characterized by neuronal loss in the striatum, ultimately leading to an ‘imbalance’ in the electrical activity of the basal ganglia-thalamocortical circuits. To restore this ‘imbalance’ in HD patients, which is held responsible for (some) of the motor symptoms, different basal ganglia nuclei have been targeted for surgical therapies, such as ablative surgery and deep brain stimulation. However, evidence to target brain nuclei for surgical therapies in HD is lacking. We reasoned that a neuronal and metabolic mapping of the basal ganglia nuclei could identify a functional substrate for therapeutic interventions. Therefore, the aim of the present study was to investigate the metabolic and neuronal activity of basal ganglia nuclei in a transgenic rat model of HD (tgHD). Subjects were 10–12month old tgHD rats and wildtype littermates. We examined the striatum, globus pallidus, entopeduncular nucleus, the subthalamic nucleus and substantia nigra at different levels. First, we determined the overall neuronal activity at a supracellular level, by cytochrome oxidase histochemistry. Secondly, we determined the subcellular metabolic activity, by immunohistochemistry for peroxisome proliferator-activated receptor-γ transcription co-activator (PGC-1α), a key player in the mitochondrial machinery. Finally, we performed extracellular single unit recordings in the nuclei to determine the cellular activity. In tgHD rats, optical density analysis showed a significantly increased cytochrome oxidase levels in the globus pallidus and subthalamic nucleus when compared to controls. PGC-1α expression was only enhanced in the subthalamic nucleus and electrophysiological recordings revealed decreased firing frequency of the majority of the neurons in the globus pallidus and increased firing frequency of the majority of the neurons in the subthalamic nucleus. Altogether, our results suggest that the globus pallidus and subthalamic nucleus play a role in the neurobiology of HD and can be potential targets for therapeutic interventions.

Spontaneous symmetry breaking in active droplets provides a generic route to motility.

We explore a generic mechanism whereby a droplet of active matter acquires motility by the spontaneous breakdown of a discrete symmetry. The model we study offers a simple representation of a "cell extract" comprising, e.g., a droplet of actomyosin solution. (Such extracts are used experimentally to model the cytoskeleton). Actomyosin is an active gel whose polarity describes the mean sense of alignment of actin fibres. In the absence of polymerization and depolymerization processes ('treadmilling'), the gel's dynamics arises solely from the contractile motion of myosin motors; this should be unchanged when polarity is inverted. Our results suggest that motility can arise in the absence of treadmilling, by spontaneous symmetry breaking (SSB) of polarity inversion symmetry. Adapting our model to wall-bound cells in two dimensions, we find that as wall friction is reduced, treadmilling-induced motility falls but SSB-mediated motility rises. The latter might therefore be crucial in three dimensions where frictional forces are likely to be modest. At a supracellular level, the same generic mechanism can impart motility to aggregates of nonmotile but active bacteria; we show that SSB in this (extensile) case leads generically to rotational as well as translational motion.

Ecosystems of invasion and metastasis in mammary morphogenesis and cancer

The present review describes molecular and cellular mechanisms of cancer invasion and metastasis as compared to mammary gland development considering communication inside and between ecosystems. At the level of the individual cell, invasion programs are written by an ecosystem of signalling pathways each of which steers several invasion-related cellular activities. At the supracellular level, communication within the epithelial compartment involves cells of the same origin, but with different phenotypes including stem cells. A similar interaction occurs between the various cells of the stromal compartment. Crucial for our understanding of tumor or mammary gland ecosystems are the mutual interactions between cells of the epithelial and cells of the stromal compartment. An update is provided for endothelial cells, cancer-associated fibroblasts and macrophages that are implicated in angiogenesis, desmoplasia and inflammation respectively. At the level of the organism, distant ecosystems, comprising primary tumor site, sites of metastasis, bone marrow and endocrine glands among others, are in continuous contact through circulating cells and soluble ligands. Our review suggests consideration of these ecosystems when designing therapeutic strategies.

Ultrastructure of cyanobacterium Nostoc sp. f. Blasia cell forms in persisting populations

Cell clusters formed in persistent populations of Nostoc sp. f. Blasia, a cyanobacterium capable of cell differentiation, under prolonged storage in the dark at low temperatures were studied for the first time. Cell reorganization was observed, including changes in the ultrastructure of thylakoids, the cell wall peptidoglycan layer, and carboxysomes. Subcellular structures involved in intercellular communication within the clusters were revealed (structures similar to microplasmodesms and contact pores, secretory vesicles, etc.) Persistence of cyanobacterial populations was concluded to result from formation not only of specialized dormant cells (akinetes), but also L-forms, as well as from the modification changes of the clustered vegetative cells. A cluster containing the vegetative cells and L-like forms within a common intercellular matrix is considered a structural unit at the supracellular level, which is responsible for survival of cyanobacterial populations when mass akinete formation does not occur.

Communication: from neurons to people; from present to future.

From its emergence out of organic chemistry and physiology a century ago, the history of biochemistry is one of shifting research agendas. For organic chemists, the questions were those of structure and composition, while for physiologists, they were questions of function. The dynamic biochemistry of the mid-20th century centred on catalysis, energy flow and metabolism. The emergence of molecular biology ('practising biochemistry without a licence') introduced information in place of energy as an organizing cellular principle, but in doing so forgot dynamics. For Crick's Central Dogma, information -- signals -- flowed in one direction only. Now, proteomics is enabling molecular biologists to rediscover biochemistry once more. Signalling -- the processes of communication across space and time -- occurs at all biological levels. I will review them, and their potential future. Will the metaphor of signalling provide a new organizing principle, one that recognizes the essentially interactive nature of information flow within metabolic webs?: I discuss first, the conservation of signalling molecules at the cellular level over evolutionary time; secondly, the supracellular level of physiological signalling in multicellular organisms -- hormones and neurons; thirdly, supraorganismic signalling and communication -- from pheromones to speech; and finally, signalling and reception within and outside the biochemical community - how do we/can we communicate with one another and the rest of the world?

Calcium signalling in tissue: diversity and domain-specific integration of individual cell response in salivary glands.

Organ function requires coordinated multicellular activities, which may require proper control of cell signalling dynamics at the supracellular level. By using high-speed confocal microscopy, we studied how calcium signalling is organised in the dissociated rat parotid gland. Salivary gland function is accomplished primarily by the compartmentalized epithelial domains, acini and ducts, the former involved in the production of primary saliva and the latter involved in its modification. Upon muscarinic stimulation with carbachol, both domains showed an increase in intracellular free calcium concentration ([Ca(2+)]i) with distinctive spatiotemporal kinetics, as indicated by the fluo-3 fluorescence. Acini responded initially, and the ducts followed with a time lag of more than 0.3 second. Cells comprising an acinus responded synchronously, whereas those in the ducts responded heterogeneously with respect to the latency period, magnitude of response and the requirement of extracellular calcium to raise [Ca(2+)]i. ATP also elicited a non-synchronous [Ca(2+)]i response in the duct domain, under a pattern different from that of carbachol. The synchronous oscillations seen in the acinar domain were made asynchronous by octanol, an agent known to inhibit gap-junction function. Accordingly, a gap junction component, connexin 32, was immunolocalised predominantly between the acinar cells. Moreover, expression of the type 2 inositol (1,4,5)-trisphosphate receptor [Ins(1,4,5)P(3)R] was homogeneous in the acinar domain but heterogeneous in the duct domain. Together, these data suggest that the calcium signalling system in salivary glands is constructed specifically according to the tissue architecture.