Spore germination in <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis>: global gene expression patterns and cell cycle landmarks

Background  

Spore germination in the yeast Saccharomyces cerevisiae is a process in which non-dividing haploid spores re-enter the mitotic cell cycle and resume vegetative growth. To study the signals and pathways underlying spore germination we examined the global changes in gene expression and followed cell-cycle and germination markers during this process.     

EGF increases expression and activity of PAs in preimplantation rat embryos and their implantation rate

Background

Embryo implantation plays a major role in embryogenesis and the outcome of pregnancy. Plasminogen activators (PAs) have been implicated in mammalian fertilization, early stages of development and embryo implantation. As in-vitro developing embryos resulted in lower implantation rate than those developed in-vivo we assume that a reduced PAs activity may be involved. In the present work we studied the effect of EGF on PAs activity, quantity and embryo implantation.

Methods

Zygotes were flushed from rat oviducts on day one of pregnancy and grown in-vitro in R1ECM supplemented with EGF (10 ng/ml) and were grown up to the blastocyst stage. The control groups were grown in the same medium without EGF. The distribution and quantity of the PAs were examined using fluorescence immunohistochemistry followed by measurement of PAs activity using the chromogenic assay. Implantation rate was studied using the embryo donation model.

Results

PAs distribution in the embryos was the same in EGF treated and untreated embryos. Both PAs were localized in the blastocysts' trophectoderm, supporting the assumption that PAs play a role in the implantation process in rats. EGF increased the quantity of uPA at all stages studied but the 8-cell stage as compared with controls. The tissue type PA (tPA) content was unaffected except the 8-cell stage, which was increased. The activity of uPA increased gradually towards the blastocyst stage and more so due to the presence of EGF. The activity of tPA did not vary with the advancing developmental stages although it was also increased by EGF. The presence of EGF during the preimplantation development doubled the rate of implantation of the treated group as compared with controls.     

Effect of mycoplasma on polyamine synthesis and levels in NIH 3T3 cells and in cells transformed by Rous sarcoma virus

Abstract Infecting NIH 3T3 cells with different species of mycoplasmas resulted only in a slight decrease in ornithine decarboxylase (ODC) activity and in the appearance of cadaverine in the infected cells. Similarly, the presence of mycoplasma in NIH 3T3 cells infected with a temperature-sensitive mutant of Rous Sarcoma virus did not bring about any significant changes either in the pattern of ODC activity or in putrescine levels, when transferred to the permissive temperature. This indicates that mycoplasmal contamination of cultures may not significantly change the putrescine metabolism in host cells. On the other hand, the presence of cadaverine in cultured cells may be attributed to contamination by mycoplasma.     

Antisense inhibition of expression of the light subunit (35 kDa) of the Gal/GalNac lectin complex inhibits Entamoeba histolytica virulence

One of the under-represented genes identified by cDNA representational difference analysis (RDA) between avirulent Entamoeba histolytica strain Rahman and virulent strain HM-1:IMSS was the amoebic light (35 kDa) subunit of the Gal/GalNac lectin complex. This lectin complex, which mediates the adhesion of the parasite to the target cell, also contains a heavy (170 kDa) subunit, which has the carbohydrate-binding domain. Stable transfectants of the virulent strain in which the expression of the 35 kDa subunit was inhibited by antisense RNA were not significantly affected in their adhesion activity to mammalian or bacterial cells but were strongly inhibited in their cytopathic activity, cytotoxic activity and in their ability to induce the formation of liver lesions in hamsters. These findings suggest that the 35 kDa subunit may have a specific function in the pathogenic pathway and provides a new insight into the role of this component of the Gal/GalNac lectin complex in amoebic virulence.     

DNA Crossover Motifs Associated with Epigenetic Modifications Delineate Open Chromatin Regions in Arabidopsis

The rate of crossover, the reciprocal exchanges of homologous chromosomal segments, is not uniform along chromosomes differing between male and female meiocytes. To better understand the factors regulating this variable landscape, we performed a detailed genetic and epigenetic analysis of 737 crossover events in Arabidopsis thaliana. Crossovers were more frequent than expected in promoters. Three DNA motifs enriched in crossover regions and less abundant in crossover-poor pericentric regions were identified. One of these motifs, the CCN repeat, was previously unknown in plants. The A-rich motif was preferentially associated with promoters, while the CCN repeat and the CTT repeat motifs were preferentially associated with genes. Analysis of epigenetic modifications around the motifs showed, in most cases, a specific epigenetic architecture. For example, we show that there is a peak of nucleosome occupancy and of H3K4me3 around the CCN and CTT repeat motifs while nucleosome occupancy was lowest around the A-rich motif. Cytosine methylation levels showed a gradual decrease within ∼2 kb of the three motifs, being lowest at sites where crossover occurred. This landscape was conserved in the decreased DNA methylation1 mutant. In summary, the crossover motifs are associated with epigenetic landscapes corresponding to open chromatin and contributing to the nonuniformity of crossovers in Arabidopsis.     

Trophoblasts isolated from the maternal circulation: in vitro expansion and potential application in non-invasive prenatal diagnosis.

Prenatal diagnosis based on rare fetal cells in maternal blood is currently not a feasible option. An effort was made to improve cell yields by targeting trophoblast cells. After sorting, the HLA-G-positive cell fraction was analyzed directly or after culture. In situ hybridization technology was applied to prove fetal cell source in samples from women carrying a male fetus and to predict gender in samples without previous knowledge of fetal sex. In vitro culture led to a significant increase in fetal cells and accurate gender prediction in 93% of these samples. This approach might be useful for non-invasive prenatal diagnosis.     

Long-Lasting Maintenance of Learning-Induced Enhanced Neuronal Excitability: Mechanisms and Functional Significance

Pyramidal neurons in the piriform cortex of olfactory discrimination trained rats show enhanced intrinsic neuronal excitability that lasts for several days after learning. Such enhanced intrinsic excitability is mediated by long-term reduction in the postburst after hyperpolarization which is generated by repetitive spike firing. The molecular machinery underlying such long-lasting modulation of intrinsic excitability, as well as its exceptional durability, is yet to be fully described. In this review, we present recent advancements that reveal the identity of the current that is modulated after learning and the second messenger system by which enhanced excitability is maintained. We also discuss the significance of such long-lasting modulation to the local network’s sensitivity to noradrenaline, a major learning-relevant neuromodulator.