Induction of synchronous growth in the yeast phase of Wangiella dermatitidis.

Synchronous yeast-phase cultures of Wangiella dermatitidis were induced by starvation, heat shock, and inhibition of deoxyribonucleic acid synthesis by hydroxyurea. Hydroxyurea-induced synchrony resulted in some distortion of the yeast-phase cell cycle. However, induction of synchrony by hydroxyurea is a rapid and simple technique which generates a marked degree of synchronous growth.     

Periodic forcing of microbial cultures: a model for induction synchrony

Periodic environmental shifts have been used to induce synchrony in many different microbial populations. In this article, the induction synchrony phenomenon is analyzed using an age distribution model in which the age at which the cells divide is subjected to periodic forcing. It is found that synchrony will occur whenever the period of the forcing lies in the interval between the youngest and the oldest division age that occur in the population during the forcing. The analysis also predicts that under certain conditions it should be possible to obtain a multimodal synchrony in which cells in the population are distributed among a set of discrete, synchronized cell lines. The behavior of the age distribution when the conditions for synchrony are not satisfied is briefly explored. It is found that the age distribution model is able to exhibit a very rich spectrum of possible dynamic behavior. Many of the phenomena observed can be thought of in terms that are familiar from nonlinear analysis, such as stable and unstable limit cycles, period doubling, halving, and chaos. The richness of dynamic behavior opens the possibility that environmental shifts or periodic forcing could be used as a powerful tool in discriminating models of microbial kinetics and cell cycle control.     

Induction of division synchrony in Tetrahymena pyriformis by a single hypoxic shock. Its use in elucidating control of the cell cycle by adenosine 3':5'-monophosphate.

A single hypoxic shock was used to induce division synchrony in Tetrahymena pyriformis. Hypoxia results in accumulation of the cells in the G2 phase of the cell cycle. Cyclic AMP and adenyl cyclase activity were measured in this system. Cell-cycle blockade was associated with extraordinarily high levels of intracellular cyclic AMP. After release from hypoxia, the cells retain a characteristic pattern of modulation of cyclic AMP associated with division that is found in selection-synchronized cells. The results are discussed with reference to other methods of induction synchrony and related studies on the natural cell cycle in this organism.     

A Continuous Synchronous Culture and Sampling System for Algae

A system has been developed for the culture of algae on a 3–5l scale under controlled axenic conditions. Light/dark regimescan be altered for the induction of synchrony and an automaticculture dilution system with new media has been developed. Theresults are shown for Platymonas striata. It was possible toinduce synchrony by a regime of 14 h light and 10 h darknessper 24 h. This synchrony could be maintained for many cyclesby the removal of half the culture daily and its replacementwith fresh medium 4 h after the onset of the light period. Cellseparation commenced at the onset of the light period and wascompleted after 4 h. No cell separation occurred during theremainder of the 24 h cycle. A system for automatic samplingof the axenic culture at known time intervals is described.     

The DnaA protein determines the initiation mass of Escherichia coli K-12

DNA replication was studied in a dnaA(Ts) strain containing a plasmid with the dnaA+ gene under plac control. At 42 degrees C, initiation of DNA replication was totally dependent upon the gratuitous inducer isopropyl beta-D-thiogalactopyranoside (IPTG). Flow cytometric measurements showed that at 13% induction of the lac promoter the growth rate, cell size, DNA content, and timing of initiation of DNA replication were indistinguishable from those observed in a wild-type control cell. Higher levels of induction resulted in initiations earlier in the cell cycle and a corresponding increase in the time from initiation to termination. We conclude that the concentration of DnaA protein determines the time of initiation and thereby the initiation mass. With an induction level equal to or above 13%, the synchrony of multiple initiations within one cell was close to that found in a wild-type control cell, showing that a cyclic variation in DnaA content is not necessary for a high degree of synchrony.     

Drifts in DNA level in the cyanobacterium Anacystis nidulans during synchrony induction and in synchronous culture

Cultures of the cyanobacterium Anacystis nidulans were synchronized by using alternating light-dark cycles. The DNA level in the cells was determined, at intervals, during pre-synchrony treatment and subsequent synchronous growth. The DNA content/cell gradually increased during synchrony induction and reached a maximum value after about 9–10 dark-light cycles, coinciding with the minimum length of pre-synchrony treatment necessary for obtaining good synchrony of cell division in our system. DNA synthesis was found to be discontinuous in the synchronous cultures. The results suggest two gaps in DNA synthesis, one occurring before and one after cell division. The results are compared with the relevant data published on the life cycle of other prokaryotic microorganisms.     

Synchrony of gene expression and the differentiation of myeloid leukemic cells: reversion from constitutive to inducible protein synthesis

There are mutant myeloid leukemic cells that cannot be induced to differentiate in serum-free culture medium, or medium with calf serum by the macrophage and granulocyte differentiation-inducing protein (MGI-2) that induces differentiation in normal myeloid cells. These mutants can be induced to differentiate by MGI-2 in medium with mouse serum. The mechanism of this induction of differentiation has been analysed by using two-dimensional gel electrophoresis to study changes in the synthesis of cytoplasmic proteins. In calf serum, 46 of the protein changes that were induced by MGI-2 in normally differentiating cells were constitutive in the differentiation-defective mutant cells. Treatment with mouse serum reverted 13 of these proteins from the constitutive to the non-constitutive state. This reversion was associated with a gain of inducibility for various differentiation-associated properties, so that 23 proteins were induced by MGI-2 for the same type of change as in normal differentiation. A normal developmental program requires synchrony of gene expression. The existence of constitutive instead of inducible gene expression can produce asynchrony in this program and thus produce blocks in differentiation. The results indicate that it is possible to treat these mutant cells so as to induce the reversion of specific proteins from the constitutive to the non-constitutive state, and that this can then restore the synchrony required for induction of differentiation. It is suggested that this mechanism may also allow induction of differentiation in other types of differentiation-defective cells.     

Antibody-induced cell-cycle synchrony

Synergism between specific antibodies and cytotoxic drugs in killing tumor cells is an established phenomenon. When cells grown in a suspension culture are treated with antibody, a subsequent increase in susceptibility to cytosine arabinoside has been shown to be due to the induction of cell-cycle synchrony. This observation may lead to a novel way of investigating cell-cycle-dependent processes and also an aspect of tumor-antibody interactions that is not generally recognized.     

Wall structure of a bitunicate ascus

Summary Ultraviolet light-induced, bleached Euglena clones exhibit synchronous steps of cell division in response to daily cycles of light and dark. The cyclic division activity, in the bleached cells, will persist in constant lighting conditions with a period, independent of temperature, of about 24 h. This persisting rhythm of cell division supports the hypothesis that this phase of the cell cycle may be coupled to the fluctuations of the endogenous circadian clock of the cell.Newly isolated bleached clones are sensitive to light in their growth rates and metabolic characteristics, showing light induced difference in substrate-stimulated respiration, and production of the polyglucan, paramylon. After repeated subculturing of a bleached clone the photosensitivity of the metabolic characteristics and of the growth rate are diminished along with the ability to photo-entrain division synchrony. Division control and the induction of cell synchrony in this organism apparently involve both the temporal influence of the endogenous cell clock and one or more other photosensitive reactions in the metabolism of the cell.A unique culture mixing technique utilizing the bleached Euglena, failed to support the hypothesis of the involvement of intercellular communication in the maintenance of cell synchrony in constant lighting conditions.     

Factors affecting phase synchronization in integrate-and-fire oscillators

Step changes in input current are known to induce partial phase synchrony in ensembles of leaky integrate-and-fire neurons operating in the oscillatory or “regular firing” regime. An analysis of this phenomenon in the absence of noise is presented based on the probability flux within an ensemble of generalized integrate-and-fire neurons. It is shown that the induction of phase synchrony by a step input can be determined by calculating the ratio of the voltage densities obtained from fully desynchronized ensembles firing at the pre and post-step firing rates. In the limit of low noise and in the absence of phase synchrony, the probability density as a function of voltage is inversely proportional to the time derivative along the voltage trajectory. It follows that the magnitude of phase synchronization depends on the degree to which a change in input leads to a uniform multiplication of the voltage derivative over the range from reset to spike threshold. This analysis is used to investigate several factors affecting phase synchronization including high firing rates, inputs modeled as conductances rather than currents, peri-threshold sodium currents, and spike-triggered potassium currents. Finally, we show that without noise, the equilibrium ensemble density is proportional to the phase response curve commonly used to analyze oscillatory systems. Action Editor: John Rinzel     

Rainfall and flowering synchrony in a tropical shrub: Variable selection on the flowering time ofErythroxylum havanense

Summary We tested the adaptive significance of flowering synchrony by means of a quantitative analysis of selection and by flowering induction experiments with the deciduous shrubErythroxylum havanense. Temporal schedules of flower and fruit production were determined for a local population (in three sites) in a Mexican seasonal forest for 2 years (1987–1988). The consequences of natural variation in flowering time (flowering initiation day) on maternal reproductive success (fecundity) were evaluated. We observed high levels of inter- and intraindividual flowering synchrony in 1987, but not in 1988 and this contrast was related to differences in rainfall patterns between the two years. A significant proportion (15.4%) of the phenotypic variation in flowering initiation day was accounted for by environmental variance. The expression of phenotypic variance of flowering time and, consequently, the opportunity for selection to act, are controlled by annual variation in rainfall. Despite the between-year difference in flowering synchrony, we detected a relatively intense directional selection on flowering initiation day in both years, but selection coefficients were of opposite sign (standardized directional gradients were –0.326 and 0.333 for 1987 and 1988, respectively). For both years there was a significant relationship between individual relative fitness and the number of neighbouring flowering plants in a given day, suggesting positive frequency-dependent selection.     

Spatial synchrony in stream fish populations: influence of species traits

Spatial synchrony in population dynamics has been identified in most taxonomic groups. Numerous studies have reported varying levels of spatial synchrony among closely‐related species, suggesting that species' characteristics may play a role in determining the level of synchrony. However, few studies have attempted to relate this synchrony to the ecological characteristics and/or life‐history traits of species. Yet, as to some extent the extinction risk may be related to synchrony patterns, identifying a link between species' characteristics and spatial synchrony is crucial, and would help us to define effective conservation planning. Here, we investigated whether species attributes and temperature synchrony (i.e. a proxy of the Moran effect) account for the differences in spatial population synchrony observed in 27 stream fish species in France. After measuring and testing the level of synchrony for each species, we performed a comparative analysis to detect the phylogenetic signal of these levels, and to construct various multi‐predictor models with species traits and temperature synchrony as covariates, while taking phylogenetic relatedness into account. We then performed model averaging on selected models to take model uncertainty into account in our parameter estimates. Fifteen of the 27 species displayed a significant level of synchrony. Synchrony was weak, but highly variable between species, and was not conserved across the phylogeny. We found that some species' characteristics significantly influenced synchrony levels. Indeed, the average model indicated that species associated with greater dispersal abilities, lower thermal tolerance, and opportunistic strategy displayed a higher degree of synchrony. These findings indicate that phylogeny and spatial temperature synchrony do not provide information pertinent for explaining the variations in species' synchrony levels, whereas the dispersal abilities, the life‐history strategies and the upper thermal tolerance limits of species do appear to be quite reliable predictors of synchrony levels.     

Application of knowledge about corpus luteum function in control of estrus and ovulation in cattle

Understanding corpus luteum (CL) function has led to development of methods of estrus synchronization in cattle that either extend the estrous cycle by administration of exogenous progestins or shorten the cycle by induction of luteolysis. Both methods have limitations, which have been reduced or overcome through sequential or combined treatment with progestin and luteolytic drugs. Future improvements in estrus synchronization methodology are most likely to come from achieving more synchrony between the development of a highly fertile ovulatory follicle and control of luteal function.     

The geography of spatial synchrony

Spatial synchrony, defined as correlated temporal fluctuations among populations, is a fundamental feature of population dynamics, but many aspects of synchrony remain poorly understood. Few studies have examined detailed geographical patterns of synchrony; instead most focus on how synchrony declines with increasing linear distance between locations, making the simplifying assumption that distance decay is isotropic. By synthesising and extending prior work, we show how geography of synchrony, a term which we use to refer to detailed spatial variation in patterns of synchrony, can be leveraged to understand ecological processes including identification of drivers of synchrony, a long‐standing challenge. We focus on three main objectives: (1) showing conceptually and theoretically four mechanisms that can generate geographies of synchrony; (2) documenting complex and pronounced geographies of synchrony in two important study systems; and (3) demonstrating a variety of methods capable of revealing the geography of synchrony and, through it, underlying organism ecology. For example, we introduce a new type of network, the synchrony network, the structure of which provides ecological insight. By documenting the importance of geographies of synchrony, advancing conceptual frameworks, and demonstrating powerful methods, we aim to help elevate the geography of synchrony into a mainstream area of study and application.     

Let’s Dance Together: Synchrony,Shared Intentionality and Cooperation

Previous research has shown that the matching of rhythmic behaviour between individuals (synchrony) increases cooperation. Such synchrony is most noticeable in music, dance and collective rituals. As well as the matching of behaviour, such collective performances typically involve shared intentionality: performers actively collaborate to produce joint actions. Over three experiments we examined the importance of shared intentionality in promoting cooperation from group synchrony. Experiment 1 compared a condition in which group synchrony was produced through shared intentionality to conditions in which synchrony or asynchrony were created as a by-product of hearing the same or different rhythmic beats. We found that synchrony combined with shared intentionality produced the greatest level of cooperation. To examinef the importance of synchrony when shared intentionality is present, Experiment 2 compared a condition in which participants deliberately worked together to produce synchrony with a condition in which participants deliberately worked together to produce asynchrony. We found that synchrony combined with shared intentionality produced the greatest level of cooperation. Experiment 3 manipulated both the presence of synchrony and shared intentionality and found significantly greater cooperation with synchrony and shared intentionality combined. Path analysis supported a reinforcement of cooperation model according to which perceiving synchrony when there is a shared goal to produce synchrony provides immediate feedback for successful cooperation so reinforcing the group’s cooperative tendencies. The reinforcement of cooperation model helps to explain the evolutionary conservation of traditional music and dance performances, and furthermore suggests that the collectivist values of such cultures may be an essential part of the mechanisms by which synchrony galvanises cooperative behaviours.     

Synchronization of the desmidStaurastrum gracile

Summary Cultures ofStaurastrum gracile maintained in a liquid medium in a 168 hours light: dark regime were asynchronous. Alteration of the regime to 1410 or 186 failed to induce synchrony, as did variation of the light and dark temperatures. The cultures were synchronized by eliminating a light period to give a total dark period of 32 hours. One such cycle gave 54% synchrony, the cells entering division at the onset of the second light period after treatment. The omission of a second light period 72 hours after the first produced no increase in the level of synchrony. The level was improved by omitting a further light period 48 hours after the first to give a 321632 induction treatment which resulted in 64% synchrony. In no instance did the cells divide between the dark treatment and the synchronized wave of cytokinesis. The mechanism of this synchrony may be explained by the existence of an essential, dark-labile division precursor.This work forms part of a thesis submitted byRoy Rowley to the University of Manchester for the degree of M.Sc.     

Population synchrony and environmental variation: an experimental demonstration

Understanding the causes of population synchrony is an important issue for population management. Its study in field populations involves disentangling the effects of dispersal and correlated environmental noise. Here we report on an experimental investigation of the synchronizing effects of noise in closed laboratory populations of a soil mite, Sancassania berlesei . Mite life-histories are highly plastic with respect to resource availability (which is a function of food supply and population density). By varying the food supply we imposed environmental variation. We show that (a) population synchrony is a function of environmental synchrony, (b) perceived population synchrony depends on the life-history stage counted, and (c) average population synchrony tends to be lower than environmental synchrony: even when populations were supplied with food with a correlation of 1.0, the correlation between populations was 0.63 (bootstrapped 95%CI 0.54–0.71). This supports recent theoretical work suggesting that the Moran theorem (indicating that population synchrony equals environmental synchrony) generally overestimates the population synchrony of nonlinear systems.     

Phase locking, the Moran effect and distance decay of synchrony: experimental tests in a model system

Spatially separated populations of many species fluctuate synchronously. Synchrony typically decays with increasing interpopulation distance. Spatial synchrony, and its distance decay, might reflect distance decay of environmental synchrony (the Moran effect), and/or short-distance dispersal. However, short-distance dispersal can synchronize entire metapopulations if within-patch dynamics are cyclic, a phenomenon known as phase locking. We manipulated the presence/absence of short-distance dispersal and spatially decaying environmental synchrony and examined their separate and interactive effects on the synchrony of the protist prey species Tetrahymena pyriformis growing in spatial arrays of patches (laboratory microcosms). The protist predator Euplotes patella consumed Tetrahymena and generated predator-prey cycles. Dispersal increased prey synchrony uniformly over both short and long distances, and did so by entraining the phases of the predator-prey cycles. The Moran effect also increased prey synchrony, but only over short distances where environmental synchrony was strongest, and did so by increasing the synchrony of stochastic fluctuations superimposed on the predator-prey cycle. Our results provide the first experimental demonstration of distance decay of synchrony due to distance decay of the Moran effect. Distance decay of the Moran effect likely explains distance decay of synchrony in many natural systems. Our results also provide an experimental demonstration of long-distance phase locking, and explain why cyclic populations provide many of the most dramatic examples of long-distance spatial synchrony in nature.     

Cell cycle synchronization of Cupriavidus necator by continuous phasing measured via flow cytometry

The continuous phasing technique was successfully used to obtain a high degree of cell cycle synchrony in cultures of the model organism Ralstonia eutropha JMP 134 (today reclassified into Cupriavidus necator). The responses of the organism were evaluated with flow cytometric determinations of DNA contents and cell size (by fluorescence and forward scatter measurements, respectively, after staining with the DNA-binding dye 4',6-diamidino-2'-phenylindole, DAPI), and cell concentration, after staining with the nucleic acid binding dye LDS-751. The strain was cultivated on a mineral medium with pyruvic acid sodium salt as the limiting carbon and energy source. Famine conditions, and thus cell dormancy, were achieved in every cycle. The best synchronization, according to the determination of DNA contents, was induced with phasing cycle durations of at least 4 h. The method allows the induction of synchrony for an indefinite period if the medium is exchanged rapidly and precisely. The results show that the time required for a complete cell cycle of Cupriavidus necator JMP 134 is independent of the chosen phasing cycle duration, provided that each process cycle lasts at least 3 h which is much longer than the time needed for a single DNA replication cycle. With shorter cycling periods DNA-synthesis is carried out in an uncoupled manner and only weak cell cycle synchrony can be attained. The results also show that DNA-synthesis can only be undertaken by cells when they have exceeded a critical size.