Defective Mitochondrial tRNA Taurine Modification Activates Global Proteostress and Leads to Mitochondrial Disease

1. Download high-res image (195KB)
2. Download full-size image

     

Neural Progenitor Cells Undergoing Yap/Tead-Mediated Enhanced Self-Renewal Form Heterotopias More Easily in the Diencephalon than in the Telencephalon

Spatiotemporally ordered production of cells is essential for brain development. Normally, most undifferentiated neural progenitor cells (NPCs) face the apical (ventricular) surface of embryonic brain walls. Pathological detachment of NPCs from the apical surface and their invasion of outer neuronal territories, i.e., formation of NPC heterotopias, can disrupt the overall structure of the brain. Although NPC heterotopias have previously been observed in a variety of experimental contexts, the underlying mechanisms remain largely unknown. Yes-associated protein 1 (Yap1) and the TEA domain (Tead) proteins, which act downstream of Hippo signaling, enhance the stem-like characteristics of NPCs. Elevated expression of Yap1 or Tead in the neural tube (future spinal cord) induces massive NPC heterotopias, but Yap/Tead-induced expansion of NPCs in the developing brain has not been previously reported to produce NPC heterotopias. To determine whether NPC heterotopias occur in a regionally characteristic manner, we introduced the Yap1-S112A or Tead-VP16 into NPCs of the telencephalon and diencephalon, two neighboring but distinct forebrain regions, of embryonic day 10 mice by in utero electroporation, and compared NPC heterotopia formation. Although NPCs in both regions exhibited enhanced stem-like behaviors, heterotopias were larger and more frequent in the diencephalon than in the telencephalon. This result, the first example of Yap/Tead-induced NPC heterotopia in the forebrain, reveals that Yap/Tead-induced NPC heterotopia is not specific to the neural tube, and also suggests that this phenomenon depends on regional factors such as the three-dimensional geometry and assembly of these cells.

     

Transformation of actin-encapsulating liposomes induced by cytochalasin D.

Liposomes encapsulating actin filaments were prepared by swelling at 0 degrees C lipid film consisting of a mixture of dimyristoyl phosphatidylcholine and cardiolipin (equal amounts by weight) in 100 microM rabbit skeletal muscle actin and 0.5 mM CaCl2 followed by polymerization of actin at 30 degrees C. Liposomes initially assumed either disk or dumbbell shape, but when cytochalasin D was added to the medium surrounding the liposomes, they were found to become spindle shaped. Liposomes containing bovine serum albumin that were given cytochalasin D and actin-containing liposomes that were given dimethylformamide, the solvent for cytochalasin D, did not transform. These results indicated actin-cytochalasin interaction is involved in the transformation process. Falling-ball viscometry and sedimentation analysis of actin solution indicated that cytochalasin cleaved actin filaments and caused depolymerization. The observation of polarized fluorescence of encapsulated actin labeled with acrylodan indicated that the actin filaments in the transformed liposomes aligned along the long axis of the liposomes. Because the actin filaments in the disk- or dumbbell-shaped liposomes formed bundles running along the liposome contour, the transformation was likely to be accompanied by the change in the actin filament arrangement in the liposomes, which was induced by actin-cytochalasin interaction.     

RAPD analysis of Aeromonas salmonicida and Aeromonas hydrophila

The randomly amplified polymorphic DNA (RAPD) technique was used to analyse the genetic differentiation of 13 strains of Aeromonas salmonicida subsp. salmonicida , and seven strains of Aer. hydrophila. Reproducible profiles of genomic DNA fingerprints were generated by polymerase chain reaction (PCR) using a single randomly designed primer. The RAPD profiles of all the non-motile aeromonads, Aer. salmonicida subsp. salmonicida were identical. However, profiles of the motile aeromonads, Aer. hydrophila differed between isolates. These findings reveal genomic homogeneity in Aer. salmonicida subsp. salmonicida and genetic variety in Aer. hydrophila strains.     

Evaluation of an antisense RNA transgene for inhibiting growth hormone gene expression in transgenic rats

We compared the levels of growth hormone (GH) mRNA in the pituitary, plasma GH concentration, and altered phenotype in rats heterozygous and homozygous for an antisense RNA transgene targeted to the rat GH gene, with those in nontransgenic rats. We initially investigated whether the transgene promoter, which is connected to four copies of a thyroid hormone response element (TRE) that increases promoter activity, affected in vivo transgene expression in the pituitary of the transgenic rats. Plasma GH concentration correlated negatively with T, injection in surgically thyroidectomized heterozygous transgenic rats. There was a reduction of about ?35–40% in GH mRNA levels in the pituitary of homozygous animals compared with those in non-transgenic rats. Plasma GH concentration was significantly ?25–32 and ?29–41% lower in heterozygous and homozygous transgenic rats, respectively, compared with that in nontransgenic animals. Furthermore, the growth rates in homozygous transgenic rats were reduced by ?72–81 and ?51–70% compared with those of their heterozygous and nontransgenic littermates, respectively. The results of these studies suggested that the biological effect of GH in vivo is modulated dose-dependently by the antisense RNA transgene. The rat GH gene can therefore be targeted by antisense RNA produced from a transgene, as reflected in the protein and RNA levels. © 1995 Wiley-Liss, Inc.     

Developmental Potentials of Early Telencephalic Neuroepithelial Cells: A Study with Microexplant Culture

To gain a better understanding of how neuron generation begins in the telencephalon, we analyzed the developmental potentials of neuroepithelial cells (NE cells) using a microexplant culture system. By the patterns of neuron generation and cell spreading on fibronectin (FN) in vitro , we recognized at least three different types of NE cells in the early (E9 to E10.5) telencephalon of mice. Although there was no transition from one growth pattern to another in vitro , these patterns were found to represent distinct stage-dependent profiles of the NE cells. (i) The youngest type of NE cells spread well and formed flat cell sheets on FN, but generated no neurons at all. (ii) An intermediate type showed extensive spreading on FN and generated a small number of neurons only early in culture. (iii) In contrast, NE cells at the most advanced stage examined formed compact cell sheets independent of FN and showed continuous neuron generation. These results indicate that telencephalic NE cells at the beginning of neurogenesis do not have a potential to make all cerebral neurons simultaneously. Our findings suggest that, during the period of E9 to E10.5, NE cells first acquire a potential to make the neurons produced before E12.5 and the NE cells then become capable of generating the neurons formed later under the influence of environmental factors.     

Genetically engineered antibodies which have reduced binding affinity for thyroxine but retain the same affinity for tri-iodothyronine

Summary Based on a three-dimensional molecular model of the variable region of a monoclonal antibody (Ab) TT1, in which the complementarity determining regions (CDRs) associate to form a cavity large enough to accommodate a single molecule of tri-iodothyronine (T3) orthyroxine (T4), we designed TT1 mutants with one amino acid substitution as candidates which have their binding affinity for T4 reduced but retain the same affinity for T3. Each candidate was subsequently tested by site-directed mutagenesis, transient expression in COS cells, and surface plasmon resonance (SPR) analysis for its binding ability for T3- or T4-conjugates with alkaline phosphatase (AP). Of the candidates, the Ab with serine in place of glycine at position 92 of the light chain (L;G92S) and the Ab with alanine in place of leucine at position 47 of the heavy chain (H;L47A) had the association constant (KA = kass / kdiss) for binding to T4-AP decreased by 5-fold, but retained the same KA for T3-AP.     

Preparation of giant liposomes in physiological conditions and their characterization under an optical microscope.

Unilamellar liposomes with diameters of 25-100 microns were prepared in various physiological salt solutions, e.g., 100 mM KCl plus 1 mM CaCl2. Successful preparation of the giant liposomes at high ionic strengths required the inclusion of 10-20% of a charged lipid, such as phosphatidylglycerol, phosphatidylserine, phosphatidic acid, or cardiolipin, in phosphatidylcholine or phosphatidylethanolamine. Three criteria were employed to identify unilamellar liposomes, yielding consistent results. Under a phase-contrast microscope those liposomes that showed the thinnest contour and had a vigorously undulating membrane were judged unilamellar. When liposomes were stained with the lipophilic fluorescent dye octadecyl rhodamine B, fluorescence intensities of the membrane of individual liposomes were integer multiples (up to four) of the lowest ones, the least fluorescent liposomes being those also judged unilamellar in the phase-contrast image. Micropipette aspiration test showed that the liposomes judged unilamellar in phase and fluorescence images had an area elastic modulus of approximately 160 dyn/cm, in agreement with literature values. The giant liposomes were stable and retained a concentration gradient of K+ across the membrane, as evidenced in fluorescence images of the K(+)-indicator PBFI encapsulated in the liposomes. Ionophore-induced K+ transport and associated volume change were observed in individual liposomes.     

Novel histone deacetylase inhibitors: design, synthesis, enzyme inhibition, and binding mode study of SAHA-based non-hydroxamates

In order to find novel non-hydroxamate histone deacetylase (HDAC) inhibitors, a series of compounds modeled after suberoylanilide hydroxamic acid (SAHA) were designed and synthesized as (i) substrate (acetyl lysine) analogues (compounds 3–7), (ii) analogues bearing various functional groups expected to chelate zinc ion (compounds 8–15), and (iii) analogues bearing nucleophilic functional groups which could bind covalently to HDACs (compounds 16–18). In this series, semicarbazide 8b and bromoacetamides 18b,c were found to be potent HDAC inhibitors for non-hydroxamates.