Antagonistic effect of selenite on tumor promoter induced cell proliferation in cultures of rat tongue epithelium

In cultures of rat tongue epithelial cells, cell proliferation following incubation with different doses of the potent tumor promoter TPA has been studied by using a stathmokinetic method counting colchicine arrested metaphases. It was demonstrated that 24 h incubation with concentrations higher than 5 ng TPA/mL medium caused inhibition, whereas below 5 ng TPA/mL medium caused stimulation of the mitotic activity reaching a maximum around 30 h from the start of the incubation period. Based on the evidence of the anticarcinogenic effect of selenium in several animal models, experiments have been performed elucidating the influence of an atoxic dose (1/1.000.000M) of selenite on the observed TPA-induced cell proliferation. Our results indicate that addition to the culture medium of an atoxic dose of selenite, not affecting the mitotic activity of control cultures, inhibits the TPA-induced stimulation of cell proliferation.     

Genes for tRNAAsp,tRNAPro, tRNATyr and two tRNAsSer in wheat mitochondrial DNA

We have begun a systematic search for potential tRNA genes in wheat mtDNA, and present here the sequences of regions of the wheat mitochondrial genome that encode genes for tRNA^Asp (anticodon GUC), tRNA^Pro (UGG), tRNA^Tyr (GUA), and two tRNAs^Ser (UGA and GCU). These genes are all solitary, not immediately adjacent to other tRNA or known protein coding genes. Each of the encoded tRNAs can assume a secondary structure that conforms to the standard cloverleaf model, and that displays none of the structural aberrations peculiar to some of the corresponding mitochondrial tRNAs from other eukaryotes. The wheat mitochondrial tRNA sequences are, on average, substantially more similar to their eubacterial and chloroplast counterparts than to their homologues in fungal and animal mitochondria. However, an analysis of regions 150 nucleotides upstream and 100 nucleotides downstream of the tRNA coding regions has revealed no obvious conserved sequences that resemble the promoter and terminator motifs that regulate the expression of eubacterial and some chloroplast tRNA genes. When restriction digests of wheat mtDNA are probed with ³²P-labelled wheat mitochondrial tRNAs, <20 hybridizing bands are detected, whether enzymes with 4 bp or 6 bp recognition sites are used. This suggests that the wheat mitochondrial genome, despite its large size, may carry a relatively small number of tRNA genes.     

Retention and structure of extracellular matrix in early chick embryos after quick-freezing and freeze-substitution

Early chick embryos, stages 11 to 14, were isolated, quick-frozen by immersion in isopentane/propane cryogen (-185 degrees C) and freeze-substituted for study by scanning electron microscopy. Emphasis was placed on the extracellular matrix (ECM) in the axial region of the segmental plate and developing somites. Ultrarapid freezing, followed by delicate freeze-substitution, immobilizes and retains much more ECM than chemical fixatives that include tannic acid (TA). The matrix on the dorsal surface of the neural tube is preserved as delicate filaments which are expressed bilaterally over the tube in a dorso-ventral orientation. These parallel primary ridges of ECM have a spacing of 1 to 3 micron, forming grooves on the wall of the neural tube. Interrupting this pattern are funnel-shaped ridges about 80 to 100 micron apart along the neural tube. The ridges become decorated with cross-bridges creating a dense lattice in the region of somite development, to the extent that a basal lamina composed of dense fibrillar network and amorphous mats of matrix accumulates on the lateral wall of the neural tube. Heavy strands and fenestrated lamellae of ECM interconnect the neural tube, notochord and somites, and attach the overlying epithelium to the upper surface of the somites. The pattern of ECM is complimentary to the migratory pathways of ventrally migrating neural crest cells and is the basis for suggesting that a physical substratum influencing the direction of neural crest cell migration is an idea that should be revived.     

Industrial yeast strain improvement: construction of strains having the killer character and capable of utilizing starch

Summary A hybrid of Saccharomyces cerevisiae with the ability to utilize starch and to produce the killer toxin was constructed by the protoplast fusion technique. The hybrid was obtained in two steps. In the first, a wild killer strain was fused with a laboratory strain (S. cerevisiae STA2). A fusion product which carried the killer factor and the ability to grow on starch was selected. In the second step, this hybrid was fused with a baker's yeast.     

Influence of the Malate-Aspartate Shuttle on Oxidative Metabolism in Synaptosomes

beta-Methyleneaspartate, a specific inhibitor of aspartate aminotransferase (EC 2.6.1.1.), was used to investigate the role of the malate-aspartate shuttle in rat brain synaptosomes. Incubation of rat brain cytosol, "free" mitochondria, synaptosol, and synaptic mitochondria, with 2 mM beta-methyleneaspartate resulted in inhibition of aspartate aminotransferase by 69%, 67%, 49%, and 76%, respectively. The reconstituted malate-aspartate shuttle of "free" brain mitochondria was inhibited by a similar degree (53%). As a consequence of the inhibition of the aspartate aminotransferase, and hence the malate-aspartate shuttle, the following changes were observed in synaptosomes: decreased glucose oxidation via the pyruvate dehydrogenase reaction and the tricarboxylic acid cycle; decreased acetylcholine synthesis; and an increase in the cytosolic redox state, as measured by the lactate/pyruvate ratio. The main reason for these changes can be attributed to decreased carbon flow through the tricarboxylic acid cycle (i.e., decreased formation of oxaloacetate), rather than as a direct consequence of changes in the NAD+/NADH ratio. Malate/glutamate oxidation in "free" mitochondria was also decreased in the presence of 2 mM beta-methyleneaspartate. This is probably a result of decreased glutamate transport into mitochondria as a result of low levels of aspartate, which are needed for the exchange with glutamate by the energy-dependent glutamate-aspartate translocator.     

Bioflavonoid interaction with rat uterine type II binding sites and cell growth inhibition

Competition analysis with a number of known bioflavonoids demonstrated that these compounds (luteolin, quercetin, pelargonin) compete for [3H]estradiol binding to cytosol and nuclear type II sites in rat uterine preparations. The inhibition of [3H]estradiol binding to type II sites was specific and these bioflavonoids did not interact with the rat uterine estrogen receptor. Since estradiol stimulation of nuclear type II sites in the rat uterus is highly correlated with cellular hypertrophy and hyperplasia, we assessed the effects of these compounds on the growth of MCF-7 human breast cancer cells in culture and on estradiol stimulation of uterine growth in the immature rat. The data demonstrated that addition of quercetin (5-10 micrograms/ml) to MCF-7 cell cultures resulted in a dose-dependent inhibition of cell growth (DNA/flask). This effect was reversible by removal of quercetin from the culture medium, or by the addition of 10 nM estradiol-17 beta to these cell cultures containing this bioflavonoid. Since estradiol-17 beta (10 nM) stimulated nuclear type II sites and proliferation of MCF-7 cells, we believe bioflavonoid inhibition of MCF-7 cell growth may be mediated through an interaction with nuclear type II sites. This hypothesis was confirmed by in vivo studies which demonstrated that injection of luteolin or quercetin blocked estradiol stimulation of nuclear type II sites in the immature rat uterus and this correlated with an inhibition of uterine growth (wet and dry weight). These studies suggest bioflavonoids, through an interaction with type II sites, may be involved in cell growth regulation.     

Loss of striatal mu1 opiate binding by substantia nigra lesions in the rat

Opiate receptors have been identified within the striatum and some have been localized presynaptically to nigrostriatal neurons. Using unilateral ablative lesions of the substantia nigra, we examined binding in the ipsilateral and contralateral striata. Lesions significantly lowered both 3H[D-Ala2,MePhe4,Gly(ol)5]enkephalin (DAGO) and 3H[D-Ala2,Leu5]enkephalin (DADL) binding. The inclusion of competitors in these assays revealed a decrease in both mu1 and mu2 receptors. Mu1 binding was slightly more sensitive to the lesioning than mu2 binding. Selective mu1 and mu2 binding assays supported these observations. No change in delta binding was observed in the lesioned striata. These studies raise the possibility that both mu1 and mu2, but not delta, receptors are localized presynaptically on nigrostriatal neurons.     

Effect of biologically active plants used as netst material and the derived benefit to starling nestlings

Summary The European starling Sturnus vulgaris preferentially incorporates fresh sprigs of particular plant species for use as nesting material. Chemicals found in these plants may act to reduce pathogen and ectoparasite populations normally found in nest environments. The present experiments were performed to test this Nest Protection Hypothesis. In the fild, we experimentally determined that wild carrot Daucus carota, a plant species preferred as nest material, effectively reduced the number of hematophagous mites found within nests relative to control nests without green vegetation. Chicks from nests containing wild carrot had higher levels of blood hemoglobin than chicks from control nests. However, there were no differences in weight or feather development. In the laboratory, we found that wild carrot and fleabane, Erigeron philadelphicus, (also preferred by starlings as nest material) substantially reduced the emergence of feeding instars of mites, while garlic mustard, Alliaria officinalis, (commonly available but not preferred) had little effect on the emergence of mites. We infer that preferred plant material may act to inhibit feeding or otherwise delay reproduction of mites, thereby reducing risk of anemia to developing nestlings.