A periodicity result for a nonlinear functional integral equation

In this paper, we study the effect of introducing a delay in a model of cell proliferation considered originally by O. Arino and M. Kimmel (J. Math. Biol. 27, 341–354 (1989)). We prove that slow oscillations take place and periodic oscillations appear for appropriate values of a parameter.     

NCI-H716 cells as a model for endocrine differentiation in colorectal cancer

In colonic neoplasms, endocrine differentiation is encountered not only in carcinoid tumors but also in adenocarcinomas, where endocrine cells may represent a distinct line of differentiation in the tumor. The significance of endocrine differentiation in colorectal cancer is not well established, partly because of the paucity of tumor cell lines which can serve as a model for studying endocrine differentiation. In this report we describe the properties of NCI-H716 cells, a cell line derived from a poorly differentiated adenocarcinoma of the caecum, under various in vitro conditions and as xenografts in athymic mice. Phenotypical properties were immunohistochemically assessed using a panel of differentiation related antibodies, and also by Northern blot analysis and by electron microscopy. Receptors for biogenic amines and peptide hormones were analyzed by ligand binding assay. These studies show that:

Construction of a new universal vector for insertional mutagenesis by homologous recombination

We describe here the construction of a vector (pSSC-9) which can be used for the insertional mutagenesis of any gene for which genomic sequences have been cloned. This vector contains a neomycin-resistance-encoding gene (neo^R) which is driven by a modified thymidine kinase (tk) promoter for positive selection. Flanking neo^R are two tk genes driven by their own promoters for negative selection of nonhomologous insertions. The neo^R and tk cassettes are separated by four unique cloning sites on the right-hand side of the neo^R cassette and three unique sites on the left-hand side. The vector also includes two SfiI sites, one on each side of the tk cassettes, for the excision of the cloned genomic DNA fragments along with the selectable markers. Electroporation of pSSC-9 into mouse embryonic stem (ES) cells and cultured diploid mouse adrenal Y-1 cells conferred resistance to G418 and sensitivity to ganciclovir in both cell lines. These results illustrate the expression of the positive and negative selectable markers in two different cell lines and thus suggest that the vector could be used in ES cells, as well as in cultured somatic cells.     

一个拖延了半个多世纪的研究课题的总结汇报

本文是汤佩松教授为北京植物生理学会1992年年会准备的发言稿,并以庆祝中国植物生理学会成立30周年。后“北京年会”因故未开,本刊应汤老要求按原样发表于此(并附英文摘要),以飨读者。     

Mass-spectrometric determination of O2 and CO2 gas exchange in illuminated higher-plant cells

In order to estimate photosynthetic and respiratory rates in illuminated photoautotrophic cells of carnation (Dianthus caryophyllus L.), simultaneous measurements of CO₂ and O₂ gas exchange were performed using ¹⁸O₂, ¹³CO₂ and a mass-spectrometry technique. This method allowed the determination, and thus the comparison, of unidirectional fluxes of O₂ and CO₂. In optimum photosynthetic conditions (i.e. in the presence of high light and a saturating level of CO₂), the rate of CO₂ influx represented 75±5% of the rate of gross O₂ evolution. After a dark-to-light transition, the rate of CO₂ efflux was inhibited by 50% whereas the O₂-uptake rate was little affected. The effect of a recycling of respiratory CO₂ through photosynthesis on the exchange of CO₂ gas was investigated using a mathematical model. The confliction of the experimental data with the simulated gas-exchange rates strongly supported the view that CO₂ recycling was a minor event in these cells and could not be responsible for the observed inhibition of CO₂ efflux. On the basis of this assumption it was concluded that illumination of carnation cells resulted in a decrease of substrate decarboxylations, and that CO₂ efflux and O₂ uptake were not as tightly coupled in the light as in the dark. Furthermore, it could be calculated from the rate of gross photosynthesis that the chloroplastic electron-transport chain produced enough ATP in the light to account for the measured CO₂-uptake rate without involving cyclic transfer of electrons around PS I or mitochondrial supplementation.Abbreviations Chl chlorophyll - K_d permeability coefficient The authors thank Drs A. Vermeglio and P. Thibault, Dépt. de Biologie, CEN-Cadarache, St. Paul Lez Durance, France, for helpful discussions.     

The effect of Cr (VI) on different inbred lines ofZea mays

Summary Four inbred lines ofZea mays (33.16, B 68, N 7B, B 77) were grown in nutrient solution to which K₂Cr₂O₇ was added to give final concentration of 5 mg/l Cr (VI). The most evident differences in metal tolerance were observed between the B 68 and 33.16 line: in fact, even though the level of Cr (VI) was almost the same in the root tissues of both lines after 6 d of treatment, in the B 68 line, Cr induced marked alterations of nuclear structure and a progressive arrest of the cell cycle in G 1. In the 33.16 line, on the contrary, the integrity of the nuclei was well preserved and the progression of the cell cycle was only barely affected.Abbreviations Cr (VI) hexavalent chromium - CRBC chick red blood cells - DAPI 4,6-diamidino-2-phenylindole - FCM Flow cytometry - FM Fluorescence microscopy - TEM Transmission electron microscopy - Tris 10 mM Tris(hydroxymethyl)aminomethane     

Targeting of T7 RNA polymerase to tobacco nuclei mediated by an SV40 nuclear location signal

We have expressed two T7 RNA polymerase genes by electroporation into tobacco protoplasts. One of the genes was modified by inserting nucleotides encoding a viral nuclear localization signal (NLS) from the large T antigen of SV40. Both T7 RNA polymerase genes directed synthesis of a ca. 100 kDa protein in the electroporated protoplasts. T7 RNA polymerase activity was detected in extracts of protoplasts electroporated with both genes. Immunofluorescence analysis of these protoplasts indicated that only the polymerase carrying the NLS accumulated in the cell nucleus. These experiments suggest that mechanisms involved in the transport from the cytoplasm to the nucleus are similar in plant and animal cells. This system demonstrates the feasibility of T7 RNA polymerase-based approaches for the high-level expression of introduced genes in plant cells.     

P-glycoprotein as multidrug transporter: a critical review of current multidrug resistant cell lines

MDR has been studied extensively in mammalian cell lines. According to usual practice, the MDR phenotype is characterized by the following features: cross resistance to multiple chemotherapeutic agents (lipophilic cations), defective intracellular drug accumulation and retention, overexpression of P-gp (often accompanied by gene amplification), and reversal of the phenotype by addition of calcium channel blockers. An hypothesis for the function of P-gp has been proposed in which P-gp acts as a carrier protein that actively extrudes MDR compounds out of the cells. However, basic questions, such as what defines the specificity of the pump and how is energy for active efflux transduced, remain to be answered. Furthermore, assuming that P-gp acts as a drug transporter, one will expect a relationship between P-gp expression and accumulation defects in MDR cell lines. A review of papers reporting 97 cell lines selected for resistance to the classical MDR compounds has revealed that a connection exists in most of the reported cell lines. However, several exceptions can be pointed out. Furthermore, only a limited number of well characterized series of sublines with different degrees of resistance to a single agent have been reported. In many of these, a correlation between P-gp expresson and transport properties can not be established. Co-amplification of genes adjacent to the mdr1 gene, mutations [122], splicing of mdr1 RNA [123], modulation of P-gp by phosphorylation [124] or glycosylation [127], or experimental conditions [26,78] could account for some of the complexity of the phenotype and the absence of correlation in some of the cell lines. However, both cell lines with overexpression of P-gp without increased efflux [i.e., 67,75] and cell lines without P-gp expression and accumulation defects/increased efflux [i.e., 25,107] have been reported. Thus, current results from MDR cell lines contradict - but do not exclude - that P-gp acts as multidrug transporter. Other models for the mechanism of resistance have been proposed: (1) An energy-dependent permeability barrier working with greater efficacy in resistant cells. This hypothesis is supported by studies of influx which, although few, all except one demonstrate decreased influx in resistant cells; (2) Resistant cells have a greater endosomal volume, and a greater exocytotic activity accounts for the efflux. Furthermore, large amounts of P-gp in the plasma membrane altering the ultrastructure and generalized changes, such as increases or decreases in membrane fluidity, alterations in lipid composition, changes in transmembrane pH gradient and membrane potential have been described in MDR cell lines and could account for some of the findings.