Synchronous Division Research Articles

Probabilistic RNA partitioning generates transient increases in the normalized variance of RNA numbers in synchronized populations of Escherichia coli

We explore the effects of probabilistic RNA partitioning during cell division on the normalized variance of RNA numbers across generations of bacterial populations. We first characterize these effects in model cell populations, where gene expression is modeled as a delayed stochastic process, as a function of the synchrony in cell division, the rate of division, and the RNA degradation rate. We further explore the additional variance that arises if the partitioning is biased. Next, in Escherichia coli cells expressing RNA tagged with MS2d-GFP, we measured the normalized variance of RNA numbers across several generations, with cell divisions synchronized by heat shock. We show that synchronized cell populations exhibit transient increases in normalized variance following cell divisions, as predicted by the model, which are not observed in unsynchronized populations. We conclude that errors in partitioning of RNA molecules generate diversity between the offspring of individual bacteria and thus constitute a form of reproductive bet-hedging.

Physical methods for synchronization of a human production cell line

Background The study of central metabolism and the interaction of its dynamics during growth, product formation and cell division are key tasks to decode the complex metabolic network of mammalian cells. For this purpose, not only the quantitative determination of key cellular molecules is necessary, but also the variation of their expression rates in time, e.g. cell cycle dependent gene expression. Thus, synchronization of cultured cells is a requisite for almost any attempt to elucidate these time dependent cellular processes. Synchronous cell growth can help to gain deeper insight into dynamics of cellular metabolism. In our work, physical methods for synchronization of the human production cell line AGE1.HN (ProBioGen AG) are experimentally tested. Cell-size distribution, DNA-content and the number of synchronous divisions are used for comparison of the methods. According to our results, the enrichment of an AGE1. HN cell population within a cell cycle phase is possible. Currently, the increase of cell yield and the improvement of conditions for cell-growth resumption after synchronization are being studied.

TDS-OFDMA: a novel multiple access system based on TDS-OFDM

As the key technology of Chinese national digital television terrestrial broadcasting (DTTB) standard, time domain synchronous OFDM (TDS-OFDM) utilizes known training sequence instead of cyclic prefix (CP) as the guard interval between adjacent inverse discrete Fourier transform (IDFT) blocks to achieve better system performance. Until now, TDS-OFDM was primarily used in downlink broadcasting. When TDS-OFDM is directly used in the uplink, it is difficult to eliminate the superposed interferences caused by different training sequences and IDFT blocks from multiple users. To solve this problem, a novel scheme called time domain synchronous orthogonal frequency division multiple access (TDS-OFDMA) is proposed in this paper. The novel space-time frame structure of the TDS-OFDMA scheme is proposed to achieve joint cyclicity reconstruction as well as joint channel estimation at the receiver. Simulation results show that the proposed scheme can achieve better bit error rate (BER) performance than conventional OFDMA system under highspeed mobile environments.

Role of the PI3K-TOR-S6K pathway in the onset of cell cycle elongation during Xenopus early embryogenesis

In the early embryogenesis of the frog, Xenopus laevis, cells proliferate by rapid and synchronous divisions, followed by cell cycle elongation and prolongation of the S phases, and then the appearance of the G2 and G1 phases after the midblastula transition (MBT). The beginning of cell cycle elongation was thought to depend on an increase in the nucleo-cytoplasmic (N/C) ratio in blastomeres and a decrease in cortical cytoplasmic factors necessary for cell cycle progression, although these factors are unknown. In the present study, we demonstrated that a regulatory subunit of PI3K (p85α) was localized in the cortical cytoplasm of the blastomere during the MBT. When the embryos were treated with a PI3K inhibitor, LY294002, or a TOR inhibitor, rapamycin, cell cycle elongation was initiated before the MBT. In addition, the inhibition of S6K expression by antisense morpholino oligo enhanced the initiation of cell cycle elongation. In contrast, the activation of PI3K-TOR by Rheb-S16H expression delayed the initiation of cell cycle elongation. These results indicate that a decrease in translational activity dependent on the PI3K-TOR-S6K pathway causes the initiation of cell cycle elongation at the onset of the MBT.

On the diversity of the primary steps of embryonic development in the caudate amphibians

Literary data on the peculiarities of the egg cleavage process in various representatives of the order of caudate amphibians consisting of 10 families have been considered. It has been recognized that in considerable number of species of Plethodontidae, Cryptobranchidae, and some other families, the synchrony of divisions is lost already after the 8-celled stage of the cleavage in large, yolk-rich and unpigmented eggs. A"standard" cleavage of early embryos of caudate amphibians, which had been described in the text-books on developmental biology and consists approximately of 10 synchronous divisions of comparatively small eggs, is characteristic only of the families Ambystomatidae and Salamandridae including 19.3% of species within the order Caudata. However, within each of these families there seems to be a number of species with a "nonstandard" type of early cleavage. The evolutionary relationships between two main types of early embryogenesis within the order Caudata are discussed.

Effect of low temperature on cell synchronization division in suspension culture cells of Pinellia ternata

To study the effect of low temperature on cell synchronization division in suspension culture cells of Pinellia ternata, in order to find a proper condition for cell synchronization. The loosened calli of P. ternata were used as materials. The effect of low temperature on cell synchronization division was studied and researched in suspension culture cells by the method of orthogonal experiment, the obtained experimental data was compared and analyzed through the analysis of range and analysis of variance. After the low temperature treatment, the cell division index was increased in various degrees, among the total results, when the temperature was set at 8 degrees C for 24 hours and then recovered for 36 hours, the effect was the best, the mitotic index was significantly increased to 11.3%. The low temperature could obviously influence the cell synchronization division in suspension culture cells of P. ternata, and the mitotic index was efficiently increased.

Anther Development Dissected

Development![Figure][1] CREDIT: [THINKSTOCK.COM][2] Anthers are the male reproductive organ of flowering plants. Unlike in animals, they originate from somatic tissue, of which a small subset of cells undergoes meiosis and develops into pollen. Kelliher and Walbot used confocal microscopy to dissect the developmental stages of the maize anther (located in the tassel at the top of the plant) to provide a timeline of anther development and maturation, from organ initiation to pollen release. They found that cell growth was regulated by neighboring tissues and that cells within the same tissue grew at different rates and within different dimensions. Of interest, although cell sizes differed, cells of similar size clustered together. This indicates that cells of the same genetic origin may undergo synchronous division. These observations are in contrast to existing models, which suggest that anthers develop through growth waves. Future studies are needed to determine the mechanisms that regulate the asymmetrical growth in neighboring cells of the same tissue, and what its function may be. Dev. Biol. 350 , 32 (2011). [1]: pending:yes [2]: http://THINKSTOCK.COM

Seasonal reproduction in a fluctuating energy environment: Insolation-driven synchronized broadcast spawning in corals

Abstract Background/Question/Methods: Colonies of spawning corals reproduce in mass-spawning events, in which polyps within each colony release sperm and eggs for fertilization in the water column, with fertilization occurring only between gametes from different colonies. Participating colonies synchronize their gamete release to a window of a few hours once a year (for the species Acropora digitifera we study experimentally). This remarkable synchrony is essential for successful coral reproduction and thus, maintenance of the coral reef ecosystem that is currently under threat from local and global environmental effects such as pollution, global warming and ocean acidification. The mechanisms determining this tight synchrony in reproduction are not well understood, although several influences have been hypothesized and studied including lunar phase, solar insolation, and influences of temperature and tides. Moreover, most corals are in a symbiotic relationship with photosynthetic algae (Symbiodinium spp.) that live within the host tissue. Experiments supported by detailed bioenergetic modeling of the coral-algae symbiosis have shown that corals receive >90% of their energy needs from these symbionts. We develop a bioenergetic integrate-and-fire model in order to investigate whether annual insolation rhythms can entrain the gametogenetic cycles that produce mature gametes to the appropriate spawning season, since photosynthate is their primary source of energy. We solve the integrate-and-fire bioenergetic model numerically using the Fokker-Planck equation and use analytical tools such as rotation number to study entrainment. Results/Conclusions: In the presence of short-term fluctuations in the energy input, our model shows that a feedback regulatory mechanism is required to achieve coherence of spawning times to within one lunar cycle, in order for subsequent cues such as lunar and diurnal light cycles to unambiguously determine the “correct” night of spawning. Entrainment to the annual insolation cycle is by itself not sufficient to produce the observed coherence in spawning. The feedback mechanism can also provide robustness against population heterogeneity due to genetic and environmental effects. We also discuss how such bioenergetic, stochastic, integrate-and-fire models are also more generally applicable: for example to aquatic insect emergence, synchrony in cell division and masting in trees.

Tracing blastomere fate choices of early embryos in single cell culture

AbstractBlastomeres of early vertebrate embryos undergo numerous fate choices for division, motility, pluripotency maintenance and restriction culminating in various cell lineages. Tracing blastomere fate choices at the single cell level in vitro has not been possible because of the inability to isolate and cultivate early blastomeres as single cells. Here we report the establishment of single cell culture system in the fish medaka, enabling the isolation and cultivation of individual blastomeres from 16- to 64-cell embryos for fate tracing at the single cell level in vitro. Interestingly, these blastomeres immediately upon isolation exhibit motility, lose synchronous divisions and even stop dividing in &8805;50% cases, suggesting that the widely accepted nucleocytoplasmic ratio controlling synchronous divisions in entire embryos does not operate on individual blastomeres. We even observed abortive division, endomitosis and cell fusion. Strikingly, ~5% of blastomeres in single cell culture generated extraembryonic yolk syncytial cells, embryonic stem cells and neural crest-derived pigment cells with timings mimicking their appearance in embryos. We revealed the maternal inheritance of key lineage regulators and their differential expression in cleavage embryos. Therefore, medaka blastomeres possess the accessibility for single cell culture, previously unidentified heterogeneity in motility, division, gene expression and intrinsic ability to generate major extraembryonic and embryonic lineages without positioning cues. Our data demonstrate the fidelity and potential of the single cell culture system for tracking blastomere fate decisions under defined conditions in vitro.

Improved Channel Estimation for TDS-OFDM Based on Flexible Frequency-Binary Padding

By adopting the pseudo-random noise (PN) sequences as the guard interval (GI) as well as the training sequence, time domain synchronous orthogonal frequency division multiplexing (TDS-OFDM) outperforms the conventional OFDM using the cyclic prefix (CP) in the spectral efficiency at the cost of the iterative padding subtraction (IPS) in channel estimation (CE). To avoid the high computational complexity of the IPS, an improved frequency domain CE scheme based on a newly designed frame structure is proposed. To further improve the CE accuracy, the time domain training sequences, which are frequency binary (FB) after the fast Fourier transform (FFT), are flexibly padded as the frame header instead of the PN sequences. Theoretical analyses and computer simulations show that the proposed scheme can improve the system performance under the time frequency doubly selective channels, even in the presence of large channel delays in the single frequency networks.

A mitotic kinesin-6, Pav-KLP, mediates interdependent cortical reorganization and spindle dynamics in Drosophila embryos

Introduction Dynamic interactions between the mitotic spindle, the cell cortex and the plasma membrane underlie many crucial cellular phenomena. For example, during cell division, the localization of the cleavage furrow is specified by the mitotic spindle (Glotzer, 2001; Scholey et al., 2003; Odell and Foe, 2008), whereas actomyosin-based cortical contractions contribute to spindle morphogenesis (Rosenblatt et al., 2004). In addition, membrane transport to the furrow is crucial for cell-cell abscission and the completion of cytokinesis (Finger and White, 2002). Recently, it has been shown that vesicles associated with F-actin are transported on furrow microtubules (MTs) (Albertson et al., 2008). However, the underlying molecular mechanisms remain largely obscure. Drosophila embryogenesis is amenable to the study of interactions between the spindle, cortex and membrane using genetic analysis, inhibitor microinjection and microscopy (Glover, 2005). In the Drosophila syncytial embryo, nuclei share the same cytoplasm and undergo 13 synchronous divisions without any intervening cytokinesis; however, following the migration of the nuclei to the embryonic surface during cycle 9, mitotic furrows form transiently around each spindle (Mazumdar and Mazumdar, 2002). The mitotic furrows grow longer during each metaphase, serving as barriers to maintain the spacing between adjacent spindles, and then regress during late anaphase and telophase. Subsequently, during interphase of cycle 14, cellularization furrows descend from the blastoderm surface to partition the nuclei into individual cells. Many studies suggest that spindle morphogenesis, as monitored by the separation of the spindle poles, depends upon a balance of forces generated by multiple molecular motors that guide the spindle through a sequence of quiescent steady states interspersed with phases of rapid spindle-pole separation (Sharp et al., 2000; Brust-Mascher et al., 2004; Cytrynbaum et al., 2005). The mitotic furrows maintain a constant distance to the poles throughout mitosis, and perturbations of mitotic molecules can cause both spindle and cortical defects during the early mitotic cycles (Cytrynbaum et al., 2005). To test the hypothesis that this force balance reflects a dynamic relationship between the spindle and the cortex, we need to know the identity of the crucial molecules that influence the structure and dynamics of both the spindle and the cortex. It is unknown how the spindle affects cortical reorganization and, conversely, how the cortex affects spindle morphogenesis. Both cellularization and metaphase furrow formation in the early Drosophila embryo are driven by the MT-dependent delivery of membrane vesicles to the furrow region (Strickland and Burgess, 2004; Riggs et al., 2003). As in conventional cytokinesis, new furrow membrane does not seem to be derived from the expansion of the pre-existing surface membrane, but rather forms through the insertion of membrane from internal stores, such as the recycling endosome (RE), Golgi or both (Lecuit and Weichaus, 2000; Sisson A mitotic kinesin-6, Pav-KLP, mediates interdependent cortical reorganization and spindle dynamics in Drosophila embryos

A novel time-domain synchronous block transmission frame structure for broadcasting return channel

In time-domain synchronous (TDS) block transmission systems, known symbols are padded in the guard interval between data blocks using some specific patterns. The complexity of channel estimation is relatively high for the time domain synchronous orthogonal frequency division multiplexing (TDS-OFDM) system. As a result, original TDSOFDM is only used for downlink broadcasting. This paper proposes a new frame structure based on TDS block transmission. The proposed frame structure can simplify the channel estimation and support the multiuser scenarios, due to the proposed padding sequence and its specific time and frequency allocation pattern. It supports the variable number of frames in one superframe, which provides the flexibility to combat various channel conditions and maintains the system efficiency. Because of these characters, it can be used in wireless uplink channel as an alternative orthogonal frequency division multiple access (OFDMA) structure. Simulation results show that the performance of the proposed frame structure is almost the same as the conventional OFDMA scheme, but has better spectrum efficiency. Therefore, it is preferred to be used in the return channel of terrestrial broadcasting systems.

A Novel CPR-TDS-OFDM System for High-Speed Mobile Reception

SUMMARY This paper proposes a novel system called the cyclic prefix reconstructable time domain synchronous orthogonal frequency division multiplexing (CPR-TDS-OFDM) system, which uses a new frame structure and restores the cyclicity of the received OFDM block with low complexity. Simulation results show that the CPR-TDS-OFDM system outperforms the conventional TDS-OFDM system in high-speed fading channels.

Frame structure for DTTB uplink systems using novel training sequences

A new frame structure based on time-domain synchronous orthogonal frequency division multiplexing for digital terrestrial television broadcasting (DTTB) uplink systems is proposed, whereby multicarrier pseudonoise (PNMC) training sequences are used as the frame header (FH). Sub-sequences of FH are inserted between signal frames as guard intervals. Simple multi-user channel estimation and equalisation can be applied and good performance is illustrated by simulations.

Differential ISI Cancellation for TDS-OFDM

A differential inter-symbol interference (ISI) cancellation method for time domain synchronous orthogonal frequency division multiplexing (TDS-OFDM) systems is proposed. The differential output of an OFDM system can greatly reduce the impact of ISI in the frequency domain and it constructs a convolutional structure, thus the Viterbi decoding algorithm can be used to recover the transmitted information from the output signal. Simulation results show the effectiveness of the proposed method.

Light can rescue auxin-dependent synchrony of cell division in a tobacco cell line

Pattern formation in plants has to cope with ambient variability and therefore must integrate environmental cues such as light. Synchrony of cell divisions was previously observed in cell files of tobacco suspension cultures, which represents a simple case of pattern formation. To develop cellular approaches for light-dependent patterning, light-responsive tobacco cell lines were screened from the cell line Nicotiana tabacum L. cv. Virginia Bright Italia 0 (VBI-0). The light responsive and auxin-autonomous cell line VBI-3 was isolated. As in the progenitor line VBI-0, cell divisions are synchronized in VBI-3 during exponential growth phase. This synchrony can be inhibited by 1-N-naphthylphthalamic acid, an auxin transport inhibitor, and this process was accompanied by the disassembly of actin filaments. However, the synchrony could be rescued when the cells were cultured under white light or with exogenous indolyl-3-acetic acid. The rescue was most efficient for continuous far-red light followed by continuous blue light, whereas continuous red light was least effective. These findings are discussed in the context of phytochrome-induced auxin biosynthesis and auxin-dependent synchrony of cell division.

DNA replication times the cell cycle and contributes to the mid-blastula transition in Drosophila embryos

We examined the contribution of S phase in timing cell cycle progression during Drosophila embryogenesis using an approach that deletes S phase rather than arresting its progress. Injection of Drosophila Geminin, an inhibitor of replication licensing, prevented subsequent replication so that the following mitosis occurred with uninemic chromosomes, which failed to align. The effect of S phase deletion on interphase length changed with development. During the maternally regulated syncytial blastoderm cycles, deleting S phase shortened interphase, and deletion of the last of blastoderm S phase (cycle 14) induced an extra synchronous division and temporarily deferred mid-blastula transition (MBT) events. In contrast, deleting S phase after the MBT in cycle 15 did not dramatically affect mitotic timing, which appears to retain its dependence on developmentally programmed zygotic transcription. We conclude that normal S phase and replication checkpoint activities are important timers of the undisturbed cell cycle before, but not after, the MBT.

A multi-user uplink TDS-OFDM system based on dual PN sequence padding

The adoption of pseudo-noise (PN) sequence instead of cyclic prefix (CP) as guard interval (GI) enables time domain synchronous orthogonal frequency division multiplexing (TDS-OFDM) outperform Cyclic Prefixed- OFDM (CP-OFDM) by spectrum efficiency but at the expense of higher complexity. Up to now, TDS-OFDM is only used in unidirectional data transmission such as downlink broadcasting. The difficulty to eliminate the implicitly mixed interferences between different PN sequences and inverse discrete Fourier transform (IDFT) blocks caused by multiple users hinders the application of TDS-OFDM in multi-user uplink scenarios. To deal with this problem, this paper proposes a multi-user uplink TDS-OFDM system based on dual PN padding (DPNP) where the cancellation of mixed interference is avoid by joint cyclicity reconstruction for all users. In addition, joint channel estimation and separation is also proposed to restore the transmitted signal for each user. Theoretical analysis and computer simulation not only verify the feasibility of the proposed system, but also show that, compared with the conventional single-user TDS-ODFM system, it holds lower implementation complexity yet even better system performance in mobile environments.

Reprogramming after Chromosome Transfer into Mouse Blastomeres

It is well known that oocytes can reprogram differentiated cells, allowing animal cloning by nuclear transfer. We have recently shown that fertilized zygotes retain reprogramming activities, suggesting that such activities might also persist in cleavage-stage embryos. Here, we used chromosome transplantation techniques to investigate whether the blastomeres of two-cell-stage mouse embryos can reprogram more differentiated cells. When chromosomes from one of the two blastomeres were replaced with the chromosomes of an embryonic or CD4(+) T lymphocyte donor cell, we observed nuclear reprogramming and efficient contribution of the manipulated cell to the developing blastocyst. Embryos produced by this method could be used to derive stem cell lines and also developed to term, generating mosaic "cloned" animals. These results demonstrate that blastomeres retain reprogramming activities and support the notion that discarded human preimplantation embryos may be useful recipients for the production of genetically tailored human embryonic stem cell lines.

A traffic grooming problem considering hub location for synchronous optical network-wavelength division multiplexing networks

In this paper, we deal with a traffic demand clustering problem for designing SONET-WDM rings. The objective is to minimize the total cost of optical add-drop multiplexers (OADMs) and inter-ring hub equipments, while satisfying intra-ring and inter-ring capacities. Also, the minimum number of nodes, for example three, for each ring should be satisfied. We develop an integer programming (IP) formulation for the problem and develop some valid inequalities that provide a tight lower bound for the problem. Dealing with the inherent computational complexity of the problem, we also devise an effective tabu search procedure for finding a feasible solution of good quality within reasonable computing time. Computational results are provided to demonstrate the efficacy of the lower and upper bound procedures for solving the problem.