A cleavage clock regulates features of lineage-specific differentiation in the development of a basal branching metazoan, the ctenophore Mnemiopsis leidyi

Background: An important question in experimental embryology is to understand how the developmental potential responsible for the generation of distinct cell types is spatially segregated over developmental time. Classical embryological work showed that ctenophores, a group of gelatinous marine invertebrates that arose early in animal evolution, display a highly stereotyped pattern of early development and a precocious specification of blastomere fates. Here we investigate the role of autonomous cell specification and the developmental timing of two distinct ctenophore cell types (motile compound comb-plate-like cilia and light-emitting photocytes) in embryos of the lobate ctenophore, Mnemiopsis leidyi. Results: In Mnemiopsis, 9 h after fertilization, comb plate cilia differentiate into derivatives of the E lineage, while the bioluminescent capability begins in derivatives of the M lineage. Arresting cleavage with cytochalasin B at the 1-, 2- or 4-cell stage does not result in blastomere death; however, no visible differentiation of the comb-plate-like cilia or bioluminescence was observed. Cleavage arrest at the 8- or 16-cell stage, in contrast, results in the expression of both differentiation products. Fate-mapping experiments indicate that only the lineages of cells that normally express these markers in an autonomous fashion during normal development express these traits in cleavage-arrested 8- and 16-cell stage embryos. Lineages that form comb plates in a non-autonomous fashion (derivatives of the M lineage) do not. Timed actinomycin D and puromycin treatments show that transcription and translation are required for comb formation and suggest that the segregated material might be necessary for activation of the appropriate genes. Interestingly, even in the absence of cytokinesis, differentiation markers appear to be activated at the correct times. Treatments with a DNA synthesis inhibitor, aphidicolin, show that the number of nuclear divisions, and perhaps the DNA to cytoplasmic ratio, are critical for the appearance of lineage-specific differentiation. Conclusion: Our work corroborates previous studies demonstrating that the cleavage program is causally involved in the spatial segregation and/or activation of factors that give rise to distinct cell types in ctenophore development. These factors are segregated independently to the appropriate lineage at the 8- and the 16-cell stages and have features of a clock, such that comb-plate-like cilia and light-emitting photoproteins appear at roughly the same developmental time in cleavage-arrested embryos as they do in untreated embryos. Nuclear division, which possibly affects DNA-cytoplasmic ratios, appears to be important in the timing of differentiation markers. Evidence suggests that the 60-cell stage, just prior to gastrulation, is the time of zygotic gene activation. Such cleavage-clock-regulated phenomena appear to be widespread amongst the Metazoa and these cellular and molecular developmental mechanisms probably evolved early in metazoan evolution

A multiplex-multicast scheme that improves system capacity of voice-over-IP on wireless LAN by 100%

Voice-over-IP (VoIP) is.an important application on the Internet. With the emergence of WLAN technology and its various advantages compared with the traditional wired LAN, it is fast becoming the 'last-mile' of choice for the overall Internet infrastructure. This work considers the support of VoIP over 802.11b WLAN. We show that although the raw WLAN capacity can potentially support more than 500 VoIP sessions, various overheads bring this down to only 12 VoIP sessions when using GSM 6.10 codec. We propose a novel multiplexing scheme for VoIP which exploits multicasting over WLAN for the downlink VoIP traffic. This scheme can achieve nearly 100% improvement in system capacity. In addition, we present results showing that the delay and delay jitter introduced by the proposed scheme are small. We believe that the scheme can reduce the blocking probability of VoIP sessions in an enterprise WLAN significantly.published_or_final_versio

Lim homeobox genes in the Ctenophore Mnemiopsis leidyi: the evolution of neural cell type specification

<p>Abstract</p> <p>Background</p> <p>Nervous systems are thought to be important to the evolutionary success and diversification of metazoans, yet little is known about the origin of simple nervous systems at the base of the animal tree. Recent data suggest that ctenophores, a group of macroscopic pelagic marine invertebrates, are the most ancient group of animals that possess a definitive nervous system consisting of a distributed nerve net and an apical statocyst. This study reports on details of the evolution of the neural cell type specifying transcription factor family of LIM homeobox containing genes (Lhx), which have highly conserved functions in neural specification in bilaterian animals.</p> <p>Results</p> <p>Using next generation sequencing, the first draft of the genome of the ctenophore <it>Mnemiopsis leidyi </it>has been generated. The Lhx genes in all animals are represented by seven subfamilies (<it>Lhx1/5, Lhx3/4, Lmx, Islet, Lhx2/9, Lhx6/8</it>, and <it>LMO</it>) of which four were found to be represented in the ctenophore lineage (<it>Lhx1/5, Lhx3/4, Lmx</it>, and <it>Islet</it>). Interestingly, the ctenophore Lhx gene complement is more similar to the sponge complement (sponges do not possess neurons) than to either the cnidarian-bilaterian or placozoan Lhx complements. Using whole mount <it>in situ </it>hybridization, the Lhx gene expression patterns were examined and found to be expressed around the blastopore and in cells that give rise to the apical organ and putative neural sensory cells.</p> <p>Conclusion</p> <p>This research gives us a first look at neural cell type specification in the ctenophore <it>M. leidyi</it>. Within <it>M. leidyi</it>, Lhx genes are expressed in overlapping domains within proposed neural cellular and sensory cell territories. These data suggest that Lhx genes likely played a conserved role in the patterning of sensory cells in the ancestor of sponges and ctenophores, and may provide a link to the expression of Lhx orthologs in sponge larval photoreceptive cells. Lhx genes were later co-opted into patterning more diversified complements of neural and non-neural cell types in later evolving animals.</p

Photoluminescence properties of the red phosphor YInGe2O7:Eu3+

Eu3+-doped YInGe2O7 phosphors were prepared via a solid-state reaction with metal oxides and their excitation and emission spectra were measured at room temperature. The results showed that pure-phase YInGe2O7 could be obtained after firing at 1250 °C. The maximum photoluminescence intensity of YInGe2O7:Eu3+ phosphor was achieved when doped with 40 mol% Eu3+ ions. Compared with Y2O2S:0.05Eu3+, the Y0.60InGe2O7:Eu3+0.40 phosphor obtained showed intense red-emission lines at 616 nm, corresponding to forced electric dipole 5D0 → 7F2 transitions of Eu3+ under 394 nm light excitation. The International Commission on Illumination chromaticity coordinates of the phosphors (x = 0.644, y = 0.356) of Y0.60InGe2O7:Eu3+0.40 were close to National Television Standard Committee standard values. As such, the synthesized phosphors may find applications in near ultraviolet InGaN chip-based white light-emitting diodes. KEY WORDS: Optical materials, X-Ray diffraction, Luminescence, Solid state reaction Bull. Chem. Soc. Ethiop. 2013, 27(2), 315-319.DOI: http://dx.doi.org/10.4314/bcse.v27i2.1

Quantifying the average and the likelihood of increases in space weather indices and in situ measurements during Solar Cycles 20–23

It is known that space weather harshly affects spacecraft performance, yet spacecraft operations and understanding the cause of anomalies can be challenging due to the complexity of environmental metrics. In this work, we analyse five metrics and in-situ measurements (Kp, Dst, and AE index, and high-energy proton and electron flux) throughout Solar Cycles 20–23 (1964 to 2008), and provide a baseline for the environment during the phases of the solar cycles (maximum, minimum, declining or ascending). We define increased activity as activity greater than two median absolute deviations (MADs) above the average activity for each phase. MAD is used, rather than standard deviation, because it is more resilient to outliers. The average and MAD values are tabulated in Table 3 to Table 6. We determine the probability that increased activity occurs 3, 14 or 30 days before a random day to distinguish between increased/quiet activities and to aid in correlating intensifications of the environment and anomalous satellite performance

Antiproliferative and apoptotic effects of angelicin in highly invasive prostate cancer cells

Purpose: To demonstrate the anti-proliferative activity of angelicin against human prostate cancer (PC- 3) cells and to evaluate its mechanismMethods: MTT (3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide) assay was used to assess the anticancer activity (growth inhibition) of angelicin in PC-3 cells. Fluorescence microscopy using Hoechst  33258 staining and inverted phase microscopy was employed to evaluate the effect of angelicin on nuclear morphology. Flow cytometry, using propidium iodide, was employed to study cell cycle-related effects of angelicin. Apoptosis induction by angelicin was examined by annexin V/PI assay.Results: Angelicin induced potent growth inhibitory effects in human prostate cancer (PC-3) cells in a  dose-dependent manner. Angelicin-treated cells exhibited chromatin condensation which implied an early  apoptotic event. Inverted phase microscopy revealed that reduction of cell population occurred with increase in the angelicin dose. Flow cytometry results showed that angelicin induced cell cycle arrest in the sub-G1 phase. Angelicin induced both early and late apoptosis in PC-3 cells following a dose-dependent pattern.Conclusion: Angelicin inhibits the growth of PC-3 human prostate cancer cells in vitro by inducing early and late apoptosis, cell cycle arrest and chromatin condensation

Enhanced ductility of nanomaterials through cooperative dislocation emission from cracks and grain boundaries

An analytical model is established to explore the cooperative mechanism between the dislocation emission from cracks and grain boundaries driven by grain boundary sliding in deformed nanocrystalline materials. In our model, high local stress concentration nearby the crack actives grain boundary sliding which creates a wedge disclination dipole at the grain boundaries’ triple junctions. The grain size-dependent criterions for the dislocation emission from the crack tip and the grain boundary are respectively derived. Influences of grain boundary sliding and grain size on the cooperative mechanism are discussed. The results show that the dislocation emission from the grain boundary is activated ahead of that from the crack tip for small grain sizes. This can explain that grain boundary sliding can toughen the nanocrystalline materials even though it suppresses dislocation emission from cracks when their grain sizes are relative small, which is because the dislocation emission from grain boundaries is activated. With the increasing grain size, the main dislocation source may transform from grain boundaries to crack tips due to grain boundary sliding. Therefore, the ductility of nanomaterials with different grain sizes can be enhanced through the cooperative dislocation emission from cracks and grain boundaries

Experiment study on the effect of iron ore sinter behavior with adding biomass

This paper focused on the effect of sinter behavior with biomass.The changes of the relevant performance indexes of this sinter behavior, emission laws of harmful gases in flue gas emissions and the mechanism of emission reduction was studied in this paper.The results showed that, when the biomass amount is 0,28 %, the sinter index can meet production requirement, the porosity of sinter increased by 18,5 %, the sinter reduction degree increased by 2,66 %, the SO2 emissions of harmful gases in the flue gas reduced by about 14 %, the amount of NOx about 19 % lower