Regulation of Cell Division in Arabidopsis

The study of cell cycle control in plants is expected to contribute to the understanding of plants' unique developmental features. The principal regulators of the eukaryotic cell cycle, namely, cyclin-dependent kinases (CDKs) and cyclins, are also conserved in plants. This review is concerned with our present knowledge on cell cycle regulation in Arabidopsis thaliana, which is widely accepted as a model plant for the study of a broad range of biological questions. Up to the present, 2 CDKs and 11 cyclins have been identified in Arabidopsis. While the expression of one of these CDKs has been found to be positively correlated with the competence of cells to divide, cyc1A1 expression of the cyclin has been almost exclusively confined to dividing cells. Although much remains to be studied concerning upstream regulators of these genes, the successful introduction of mutant CDKs into plants demonstrates the potential of using such an approach to intentionally modulate the plant cell cycle and development.     

High affinity binding site for nuclear factor I next to the hepatitis B virus S gene promoter.

The hepatitis B virus (HBV) surface antigen (HBsAG) is encoded by the S gene under the regulation of a promoter in the pre-S1 region. The S gene promoter does not contain a 'TATA' box-like sequence, but there is a sequence resembling, in part, the late promoter of Simian virus 40 (SV40). In an attempt to study the regulation of the S gene promoter we looked for cellular proteins which bind to this region. We report here that a nuclear protein is tightly bound to the HBV genome at a position approximately 190 bases upstream from the S gene promoter. Evidence is provided to show that (a) this nuclear protein is the nuclear factor I (NF-I) that was previously found to be bound to the inverted terminal repeat of the adenovirus (Ad) DNA and to enhance Ad DNA replication in vitro and (b) this NF-I binding site is required for optimal activity of the S gene promoter.     

Agonist-specific reverse regulation of muscarinic receptors by transition metal ions and guanine nucleotides

Transition metal ions, e.g. Mn²⁺, Ni²⁺ and Co²⁺ enhance $\text{in vitro}$ agonist binding to muscarinic receptors in mouse cortex or hippocampus. This effect arises mainly from the conversion of low to high affinity binding sites. Binding properties of antagonists in these brain areas, as well as those of both agonists and antagonists of medulla-pons muscarinic receptors, are insensitive to these ions. The induced interconversion can be reversed by either of the following procedures: (i) removal of the ions; (ii) thermal exposure; (iii) addition of micromolar concentrations of guanine nucleotides.     

Bacilliform inclusions in cells of the proximal pars distalis in the pituitary of four species of Tilapia (Teleostei)

Summary Thin sections and replicas of freeze-etched pituitaries from six species of the teleostean family of Cichlidae were studied by electron microscopy. Four species belonging to the genus Tilapia exhibit rod-like structures, i.e., bacilliform inclusions (BI), about 1–2 m in length in cells of the proximal Pars distalis. The BI are found either isolated or fused in small groups. They are enclosed in an envelope similar to that of secretory granules. Both the BI and the secretory granules give a positive PAS-reaction.Abbreviations BI bacilliform inclusion - GTH gonadotroph hormone - STH somatotroph hormone - TSH thyrotroph hormone This research was supported by a grant from the National Council for Research and Development, Israel, and the GKSS Geesthacht-Tesperhude, Germany     

Large scale production of human lymphoblastoid (Namalva) interferon

Summary Large scale production of human lymphoblastoid (Namalva) interferon (IF) is described. Cell propagation, in up to 50 1 culture volume, was carried out in a low cost medium by a semi-continuous cultivation method. IF was induced by Sendai virus, testing two induction methods. The yield of crude IF varied in the range of 12 – 100 × 10³ IF units.ml^-1. A weekly production output of 1 – 5 × 10⁸ units crude IF was obtained.     

The S promoter of hepatitis B virus is regulated by positive and negative elements.

The S promoter, one of the major hepatitis B virus (HBV) promoters, directs the synthesis of mRNA for surface antigen. Transient expression studies revealed that this promoter is highly active in the Alexander hepatoma cell line but not in SK-Hep1 and HeLa cells. We found that a distal element of the promoter (-103 to -48) confers this cell-type-specific behavior through a mechanism in which the promoter activity is repressed in HeLa and SK-Hep1 cells but increased in Alexander cells. By using an inhibitor of protein synthesis, we obtained evidence that a labile repressor(s) confers the negative effect in SK-Hep1 cells. We also found an enhancerlike activity associated with a small DNA segment of the S promoter (-27 to + 30). This proximal element was active in HeLa and SK-Hep1 cells only in the absence of the distal negative element. Finally, analysis of S promoter deletion mutants demonstrated that the -27 to -17 region of the S promoter is crucial for its activity.     

An immobilized hybridoma culture perfusion system for production of monoclonal antibodies

A fixed bed perfusion system for hybridoma cell immobilization is presented. The system consists of a culturing vessel (300 ml total volume) in which polyurethane (PU) sponges in the form of small cubes of about 5 mm sides are packed. Cells are immobilized by physical entrapment in the foam matrix. By entrapment of the cells in the pores of the matrix high cell concentration can be maintained in a mechanically protected environment. Medium is continuously circulated by an airlift pump mounted in the cell-free chamber (700 ml total volume).Medium flow rate, feeding rate, dissolved oxygen, pH, nutrient uptake and waste product formation can be easily monitored and controlled. Steady state conditions are established with medium dilution rates of 1.0–1.5 reactor volume per day. The steady state is characterized by a constant cell density, constant culture volume and constant glucose and lactate levels. Cell-free supernatant is collected continuously in a cold room adjacent to the 37°C culture room. Monoclonal antibodies (MAb) are produced at a concentration of 150–200 g/ml for several weeks. An important feature of the system is the capacity to maintain a population of cells after the growth phase in a non-proliferating state for extended time periods expressing high titers of MAb.Abbreviations DO Dissolved Oxygen - FBS Fetal Bovine Serum - FBR Fixed Bed Reactor - MAb Monoclonal Antibody - PU polyurethane     

Persistence of [14C] gibberellin A3 and [3H] gibberellin A1 in senescing,ethylene treated Citrus and tomato fruit

The fate of [¹⁴C] gibberellin A₃ and [³H] gibberellin A₁ was examined in senescing fruit of Shamouti orange (Citrus sinensis L. Osbeck) and tomato (Lycopersicon esculentum Mill.). Gibberellin A₃ was highly persistent in Citrus peel (t 1/2=18 days) and to a lesser degree in tomato (t 1/2=5.5 days). Ethylene and ethephon caused a slight enhancement of gibberellin A₃ metabolism in Citrus and tomato fruit, respectively. Gibberellin A₁ was metabolized by Citrus peel at a relatively high rate (t 1/2 < 24 h) and ethylene slightly reduced this rate. It is concluded that the ethylene-induced enhancement of senescence does not involve major effects on the deactivation of applied gibberellins.Abbreviations GA₃ gibberellin A₃ - GA₁ gibberellin A₁     

Application of FTIR microscopy for the characterization of malignancy: H-ras transfected murine fibroblasts as an example.

Recently, microscopic FTIR is widely used in the field of biology and medicine. FTIR can detect biomolecular changes in the cells and tissues responsible for various disorders. In this report, we characterize the H-ras transfected fibroblasts and its normal control using microscopic FTIR. The intensity of the normal fibroblasts was higher than that of H-ras transfected fibroblasts. Our studies showed significant differences occur in the concentration of vital metabolites upon transformation. The DNA and carbohydrates level decreased in the transformed cells compared to the controls. A linear correlation could be found between the levels of carbohydrates and phosphate, while the RNA/DNA ratio varied inversely with glucose/phosphate levels.