Role of the outer tissue in abscisic acid-mediated growth suppression of etiolated squash hypocotyl segments

Exogenously applied abscisic acid (ABA) substantially suppressed the elongation of hypocotyl segments of etiolated squash ( Cucurbita maxima Duch. cv. Houkou-Aokawaamaguri) after a 3 h lag period, without changes in the osmolalities of the apoplastic and symplastic solutions in the segment.
Segments with the outer tissues removed elongated more rapidly than unpeeled segments (whole segments). ABA did not suppress the elongation of peeled segments. When the segments were incubated in [¹⁴C]-glucose, radioactivity was more effectively incorporated into the cell wall fractions of the outer than into those of the inner tissue. ABA significantly inhibited the incorporation of radioactivity into hermicellulose and cellulose of the outer tissue prior to the suppression of segment elongation, but it did not inhibit the incorporation into the pectic traction of the outer tissue or into any of the cell wall fractions of the inner tissue. These results indicate that ABA primarily affected the outer tissue, in which it specifically reduced the synthesis of hemicellulose and cellulose prior to the ABA-mediated suppression of growth.     

Effects of detergents on the secondary structures of prion protein peptides as studied by CD spectroscopy.

Pathogenic prion proteins (PrP(Sc)) are thought to be produced by alpha-helical to beta-sheet conformational changes in the normal cellular prion proteins (PrP(C)) located solely in the caveolar compartments. In order to inquire into the possible conformational changes due to the influences of hydrophobic environments within caveolae, the secondary structures of prion protein peptides were studied in various kinds of detergents by CD spectra. The peptides studied were PrP(129-154) and PrP(192-213); the former is supposed to assume beta-sheets and the latter alpha-helices, in PrP(Sc). The secondary structure analyses for the CD spectra revealed that in buffer solutions, both PrP(129-154) and PrP(192-213) mainly adopted random-coils (approximately 60%), followed by beta-sheets (30%-40%). PrP(129-154) showed no changes in the secondary structures even in various kinds of detergents such as octyl-beta-D-glucopyranoside (OG), octy-beta-D-maltopyranoside (OM). sodium dodecyl sulfate (SDS), Zwittergent 3-14 (ZW) and dodecylphosphocholine (DPC). In contrast, PrP(192-213) changed its secondary structure depending on the concentration of the detergents. SDS, ZW, OG and OM increased the alpha-helical content, and decreased the beta-sheet and random-coil contents. DPC also increased the alpha-helical content, but to a lesser extent than did SDS, ZW, OG or OM. These results indicate that PrP(129-154) has a propensity to adopt predominantly beta-sheets. On the other hand, PrP(192-213) has a rather fickle propensity and varies its secondary structure depending on the environmental conditions. It is considered that the hydrophobic environments provided by these detergents may mimic those provided by gangliosides in caveolae, the head groups of which consist of oligosaccharide chains containing sialic acids. It is concluded that PrP(C) could be converted into a nascent PrP(Sc) having a transient PrP(Sc) like structureunder the hydrophobic environments produced by gangliosides.     

OCCURRENCE OF AN ISOPRENOID C25 DIUNASATURATED ALKENE AND HIGH NEUTRAL LIPID CONTENT IN ANTRACTIC SEA-ICE DIATOM COMMUNITIES1

The lipid and hydrocarbon composition of natural populations of diatom communities collected during the austral spring bloom of 1985 in the sea-ice at McMurdo Sound, Antartica was analyzed by TLC-FID, GC and GC-MS. Sea-ice diatom communities were dominated by Amphiprora sp., Nitzschia stellata Manguin and Berkeleya sp. at Cape Armitage; N. stellata, Amphiprora, Pleurosigma, N. kerguelensis (O'Meara) Hasle and some small centric diatoms adjacent to the Erebus Ice Tongue; and Porosira pseudodenticulata (Hustedt) Jouse at Wohlschlag Bay. Lipid distributions of the sea ice diatom communities from the Cape Armitage and Ereus sites were characterized by high concentrations of tracylaglecycerol (triacylglycerolplar lipid = 1.0 to 1.5). The hydrocarbon n-C_21:6, common in temperate diatoms, and an isoprenoid C₂₅ diunsaturated alkene were the dominant hydrocarons detected at these two sites. Hydrogenation of the C₂₅ diene produced the known alkane 2, 6, 10, 14-tetramethyl-7- (3-methylpentyl)-pentadecane. The C₂₅ diene is one of several structurally related hydrocarbons reported in many estuarine, coastal and ocean ic sediments. We propose that certain species of diatoms are a likely source of these alkenes in sediments. The first reported biological occurrence of the C₂₅ diene in the green seaweed Enteromorpha prolifera may have been due to the presence of epiphytic microalgae in the field sample analysed.     

Upregulation of Fas-induced apoptosis by interferon-γ accompanied by increased ICE expression in renal cell cancer cells

The integration of Fas/Apo-1 (CD95) by Fas ligand or anti-Fas antibody induces apoptosis, and this system plays a pivotal role for the lysis of target cells by cytotoxic T lymphocytes. Fas-mediated apoptosis is also increased by a prior incubation of Fas-bearing cells with interferon(IFN)-. Interleukin-1- converting enzyme (ICE) and/or CPP32, or other members of ICE family act as direct cell death executors downstream of this mechanism, and a tetrapeptide inhibitor of these cysteine proteases blocks Fas-mediated apoptosis. In this study, we examined the effect of IFN- on Fas-mediated apoptosis in ACHN cells. IFN- augmented apoptosis in a dose dependent manner and reached a plateau at 400 U/ml when exposed for 48 h before the end of culture. The kinetics revealed a significant increase in apoptosis after 24 h. Exposing ACHN cells to IFN- increased pro-ICE expression accompanied with a decrease of pro-CPP32. These results suggest that direct enhancement of ICE expression and/or upregulation of conversion of pro-CPP32 to active form increases Fas-mediated apoptosis by IFN- in ACHN cells.     

Glutamine metabolism in AS-30D hepatoma cells. Evidence for its conversion into lipids via reductive carboxylation

A study was undertaken to assess the role of a physiological concentration of glutamine in AS-30D cell metabolism. Flux of¹⁴C-glutamine to¹⁴CO₂ and of¹⁴C-acetate to glutamate was detected indicating reversible flux between glutamate and TCA cycle -ketoglutarate. These fluxes were transaminase dependent. A flux analysis was compared using data from three tracers that label -ketoglutarate carbon 5, [2-¹⁴C]glucose, [1-¹⁴C]acetate and [5-¹⁴C]glutamine. The analysis indicated that the probability of flux of TCA cycle -ketoglutarate to glutamate was, at minimum, only slightly less than the probability of flux of -ketoglutarate through -ketoglutarate dehydrogenase. The apparent Km for oxidative flux of [¹⁴C]glutamine to¹⁴CO₂, 0.07 mM, indicated that this flux was at a maximal rate at physiological, 0.75 mM, glutamine. Although oxidative flux through -ketoglutarate dehydrogenase was the major fate of glutamine, flux of glutamine to lipid via reductive carboxylation of -ketoglutarate was demonstrated by measuring incorporation of [5-¹⁴C]glutamine into¹⁴C-lipid. In media containing glucose (6 mM), and glutamine (0.75 mM) 47 per cent of the lipid synthesized from substrates in the media was derived from glutamine via reductive carboxylation and 49 per cent from glucose. These findings of nearly equal fluxes suggest that lipogenesis via reductive carboxylation may be an important role of glutamine in hepatoma cells.     

Coloboma Hyperactive Mutant Mice Exhibit Regional and Transmitter-Specific Deficits in Neurotransmission

Abstract: The mouse mutant coloboma ( Cm /+), which exhibits profound spontaneous hyperactivity and bears a deletion mutation on chromosome 2, including the gene encoding synaptosomal protein SNAP-25, has been proposed to model aspects of attention-deficit hyperactivity disorder. Increasing evidence suggests a crucial role for SNAP-25 in the release of both classical neurotransmitters and neuropeptides. In the present study, we compared the release of specific neurotransmitters in vitro from synaptosomes and slices of selected brain regions from Cm /+ mice with that of +/+ mice. The release of dopamine (DA) and serotonin (5-HT) from striatum, and of arginine vasopressin and corticotropin-releasing factor from hypothalamus and amygdala is calcium-dependent. Glutamate release from and content in cortical synaptosomes of Cm /+ mice are greatly reduced, which might contribute to the learning deficits in these mutants. In dorsal striatum of Cm /+ mutants, but not ventral striatum, KCI-induced release of DA is completely blocked and that of 5-HT is significantly attenuated, suggesting that striatal DA and 5-HT deficiencies may be involved in hyperactivity. Further, although acetylcholine failed to induce hypothalamic corticotropin-releasing factor release from Cm /+ slices, restraint stress increased plasma corticosterone levels in Cm /+ mice to a significantly higher level than in +/+ mice, suggesting an important role for arginine vasopressin in hypothalamic-pituitary-adrenal axis activation. These results suggest that reduced SNAP-25 expression may contribute to a region-specific and neurotransmitter-specific deficiency in neurotransmitter release.     

Characterization of the Palmitoylation Domain of SNAP-25

Abstract: SNAP-25 (synaptosomal associated protein of 25 kDa) is a neural specific protein that has been implicated in the synaptic vesicle docking and fusion process. It is tightly associated with membranes, and it is one of the major palmitoylated proteins found in neurons. The functional role of palmitoylation for SNAP-25 is unclear. In this report, we show that the palmitate of SNAP-25 is rapidly turned over in PC12 cells, with a half-life of ∼3 h, and the half-life for the protein is 8 h. Mutation of Cys to Ser at positions 85, 88, 90, and 92 reduced the palmitoylation to 9, 21, 42, and 35% of the wild-type protein, respectively. Additional mutations of either Cys^85,88 or Cys^90,92 nearly abolished palmitoylation of the protein. A similar effect on membrane binding for the mutant SNAP-25 was observed, which correlated with the degree of palmitoylation. These results suggest that all four Cys residues are involved in palmitoylation and that membrane association of SNAP-25 may be regulated through dynamic palmitoylation.     

Reconstruction of the STS 14 (Australopithecus africanus) pelvis

The study reports a reconstruction of the sacrum in STS 14 based on extrapolation from the measurements of the first two sacral vertebrae of STS 14 and of the angle formed by the anterior surfaces of their vertebral bodies. Reconstruction is based on comparisons of, and extrapolation from, sacra of Pan troglodytes, Homo sapiens, and Australopithecus afarensis. The reconstructed sacrum has an anterior sacral curvature of 39°. The two ossa coxae were also completed by mirror imaging of one side by the other. With the pelvis completely reconstructed, the pelvic dimensions for the antero-posterior (AP) diameters of the pelvic inlet, midpelvis, and pelvic outlet are 85, 68, and 69 mm and the corresponding transverse (TR) diameters are 109, 88, and 103 mm, respectively. The posterior sagittal diameters in the three pelvic planes are small compared to the anterior sagittal diameters. This analysis indicates that the STS 14 pelvis is platypelloid in the three pelvic planes; i.e., all the AP diameters are smaller than the corresponding TR diameters. This makes the STS 14 pelvis similar to that to Al 288-1, save for a less pronounced degree of platypelloidy at the inlet in the former. © 1995 Wiley-Liss, Inc.     

Calcium transport in epithelial cells of the intestine and kidney

The central role of 1α,25-dihydroxyvitamin D₃ in the regulation of calcium balance is well established. By increasing the absorption of calcium in the intestine and the reabsorption of filtered calcium in the kidney tubule, the hormone maintains an appropriate calcium balance. The cellular mechanisms that underlie the increase in calcium transport in epithelial cells in response to 1α,25-dihydroxyvitamin D₃ are beginning to be defined. These events include an increase in the movement of calcium across the apical membrane of the cell, an increase in the movement of calcium across the cell, and an increase in the extrusion of calcium at the basolateral portion of the cell. In this Prospects article, I will discuss the nature of the various processes and proteins involved in transcellular calcium movement, and I will attempt to highlight various future areas of research.