Zinc Deficiency and Anther Development in Maize

With the onset of male reproductive phase at 28 days, zinc waswithdrawn from fifty percent of maize (Zea mays L. cv. Ganga2) plants grown in refined sand at 0.13 mg Zn liter^–1.Plants from which zinc was withdrawn developed zinc deficiencysymptoms in young leaves after 38 days and were low in tissuezinc. Their tassel formation and pollen development was retarded.Anthers failed to develop beyond freshly liberated young pollengrain stage and vessels were formed in place of sporogenoustissue in sixty percent anthers of the younger of the two florets.Anthers from these plants showed low zinc concentration andstimulated specific activities of catalase, peroxidase, ribonucleaseand acid phosphatase. On resuming normal zinc (0.13 mg Zn liter^–1) through rootsto the plants from which it was withdrawn for 17 days, vegetativegrowth was partially renewed and short axillary buds were formedbut the development of anthers remained retarded. (Received April 11, 1986; Accepted October 15, 1986)     

The involvement of O-linked oligosaccharide chains of the sea urchin egg receptor for sperm in fertilization

Recent investigations on the sea urchin egg receptor for spermhave led to its sequencing and the demonstration that it isa 350 kDa glycoprotein. In the current study, the N- and O-linkedoligosaccharide chains were cleaved from the protein fractionatedon concanavalin A-agarose. The putative O-linked oligosaccharidechains that did not bind to the lectin were further fractionatedby anion-exchange chromatography. Using a competition bioassaythat measured the ability of these oligosaccharide chains toinhibit fertilization, it was found that the N-linked chainswere devoid of inhibitory activity. Rather, the inhibitory activitywas localized to the O-linked chains, with the most highly charged,sulphated chains showing the highest inhibitory activity. Thebioactive oligosaccharides were labelled by reduction and assayedfor binding to sperm. The results of the binding assay, coupledwith the fertilization bioassay, indicate that the oligosaccharidesinhibit fertilization by binding to acrosome-reacted sperm.The bioactive oligosaccharide lacked species specificity infertilization bioassays, unlike the intact receptor and a recombinantaglyco protein containing only the extracellular domain of thereceptor. Since previous work showed that the recombinant proteininhibits fertilization species specifically and binds to acrosome-reactedsperm, a two-step model of sperm-egg interaction is proposed.The first step is postulated to be a low-affinity ionic interactionof the sulphated O-linked oligosaccharide chains of the receptorwith sperm that is not species specific. This is followed bya high affinity, species-specific interaction of the sperm withone or more binding sits on the polypeptide chain of the receptor. fertilization oligosaccharide receptor sea urchin egg sea urchin sperm     

Synthesis and Conformational Studies of O 5′, 6-Methanouridine—A New Type of Pyrimidine Cyclonucleoside

Abstract

The 5-oxo-6-methylene-pyrimidine-2,4-dione intermediate (6) that is formed when 5-acetoxy-6-acetoxymethyl-1-β-D-(5-O-acetyl-2,3-O-isopropylidene)-ribofuranosyluracil (5) is treated with sodium hydroxide undergoes cyclization at pH 14 to give 2′,3′-O-isopropylidene-5-hydroxy- O ⁵, 6-methanouridine (8) in good yield. Conversion of 8 into the 5-triflate ester 14 followed by reduction with [(Ph)₃P]₄Pd/Bu₃SnH and deblocking with acetic acid then affords O ^5′, 6-methanouridine (4) Conformational studies (NOE difference spectra, vicinal ¹H-¹³C coupling constants, NOESY and CD spectra, molecular modeling) indicate that the C7-methylene group of 4 projects towards the furanose ring oxygen atom, producing a glycosyl rotation angle of about ? 160°.     

Controlled Release of Ropinirole Hydrochloride from a Multiple Barrier Layer Tablet Dosage Form: Effect of Polymer Type on Pharmacokinetics and IVIVC

The purpose of the present study was to control in vitro burst effect of the highly water-soluble drug, ropinirole hydrochloride to reduce in vivo dose dumping and to establish in vitro–in vivo correlation. The pharmacokinetics of two entirely different tablet formulation technologies is also explored in this study. For pharmacokinetics study, FDA recommends at least 10% difference in drug release for formulations to be studied but here a different approach was adopted. The formulations F8A and F9A having similar dissolution profiles among themselves and with Requip® XL™ (f₂ value 72, 77, 71 respectively) were evaluated. The C_max of formulation F8A comprising hypromellose 100,000 cP was 1005.16 pg/ml as compared to 973.70 pg/ml of formulation F9A comprising hypromellose 4000 cP irrespective of T_max of 5 and 5.75 h, respectively. The difference in release and extent of absorption in vivo was due to synergistic effect of complex RH release mechanism; however, AUC_0–t and AUC_0–∞ values were comparable. The level A correlation using the Wagner–Nelson method supported the findings where R² was 0.7597 and 0.9675 respectively for formulation F8A and F9A. Thus, in vivo studies are required for proving the therapeutic equivalency of different formulation technologies even though f₂ ≥ 50. The technology was demonstrated effectively at industrial manufacturing scale of 200,000 tablets.KEY WORDS: controlled release polymer, in vitro–in vivo correlation (IVIVC), multiple barrier layer tablets, pharmacokinetics, ropinirole hydrochloride (RH)     

Tristetraprolin Mediates Radiation-Induced TNF-α Production in Lung Macrophages

The efficacy of radiation therapy for lung cancer is limited by radiation-induced lung toxicity (RILT). Although tumor necrosis factor-alpha (TNF-α) signaling plays a critical role in RILT, the molecular regulators of radiation-induced TNF-α production remain unknown. We investigated the role of a major TNF-α regulator, Tristetraprolin (TTP), in radiation-induced TNF-α production by macrophages. For in vitro studies we irradiated (4 Gy) either a mouse lung macrophage cell line, MH-S or macrophages isolated from TTP knockout mice, and studied the effects of radiation on TTP and TNF-α levels. To study the in vivo relevance, mouse lungs were irradiated with a single dose (15 Gy) and assessed at varying times for TTP alterations. Irradiation of MH-S cells caused TTP to undergo an inhibitory phosphorylation at Ser-178 and proteasome-mediated degradation, which resulted in increased TNF-α mRNA stabilization and secretion. Similarly, MH-S cells treated with TTP siRNA or macrophages isolated from ttp (−/−) mice had higher basal levels of TNF-α, which was increased minimally after irradiation. Conversely, cells overexpressing TTP mutants defective in undergoing phosphorylation released significantly lower levels of TNF-α. Inhibition of p38, a known kinase for TTP, by either siRNA or a small molecule inhibitor abrogated radiation-induced TNF-α release by MH-S cells. Lung irradiation induced TTP^Ser178 phosphorylation and protein degradation and a simultaneous increase in TNF-α production in C57BL/6 mice starting 24 h post-radiation. In conclusion, irradiation of lung macrophages causes TTP inactivation via p38-mediated phosphorylation and proteasome-mediated degradation, leading to TNF-α production. These findings suggest that agents capable of blocking TTP phosphorylation or stabilizing TTP after irradiation could decrease RILT.     

Induction of spine growth and synapse formation by regulation of the spine actin cytoskeleton

We explored the relationship between regulation of the spine actin cytoskeleton, spine morphogenesis, and synapse formation by manipulating expression of the actin binding protein NrbI and its deletion mutants. In pyramidal neurons of cultured rat hippocampal slices, NrbI is concentrated in dendritic spines by binding to the actin cytoskeleton. Expression of one NrbI deletion mutant, containing the actin binding domain, dramatically increased the density and length of dendritic spines with synapses. This hyperspinogenesis was accompanied by enhanced actin polymerization and spine motility. Synaptic strengths were reduced to compensate for extra synapses, keeping total synaptic input per neuron constant. Our data support a model in which synapse formation is promoted by actin-powered motility.     

Localization and interaction of NHERF isoforms in the renal proximal tubule of the mouse

In expression systems and in yeast, Na/H exchanger regulatory factor (NHERF)-1 and NHERF-2 have been demonstrated to interact with the renal brush border membrane proteins NHE3 and Npt2. In renal tissue of mice, however, NHERF-1 is required for cAMP regulation of NHE3 and for the apical targeting of Npt2 despite the presence of NHERF-2, suggesting another order of specificity. The present studies examine the subcellular location of NHERF-1 and NHERF-2 and their interactions with target proteins including NHE3, Npt2, and ezrin. The wild-type mouse proximal tubule expresses both NHERF-1 and NHERF-2 in a distinct pattern. NHERF-1 is strongly expressed in microvilli in association with NHE3, Npt2, and ezrin. Although NHERF-2 can be detected weakly in the microvilli, it is expressed predominantly at the base of the microvilli in the vesicle-rich domain. NHERF-2 appears to associate directly with ezrin and NHE3 but not Npt2. NHERF-1 is involved in the apical expression of Npt2 and the presence of other Npt2-binding proteins does not compensate totally for the absence of NHERF-1 in NHERF-1-null mice. Although NHERF-1 links NHE3 to the actin cytoskeleton through ezrin, the absence of NHERF-1 does not result in a generalized disruption of the architecture of the cell. Thus the mistargeting of Npt2 seen in NHERF-1-null mice likely represents a specific disruption of pathways mediated by NHERF-1 to achieve targeting of Npt2. These findings suggest that the organized subcellular distribution of the NHERF isoforms may play a role in the specific interactions mediating physiological control of transporter function.     

NHERF-1 uniquely transduces the cAMP signals that inhibit sodium-hydrogen exchange in mouse renal apical membranes

Sodium-hydrogen exchanger regulatory factor isoform-1 (NHERF-1) and NHERF-2 are two structurally related PDZ-domain-containing protein adapters that effectively transduce cyclic AMP (cAMP) signals that inhibit NHE3, the sodium-hydrogen exchanger isoform present at the apical surface of kidney and gut epithelia. The mouse renal proximal tubule expresses both NHERF isoforms, suggesting their redundant functions as regulators of renal electrolyte metabolism. To define the role of NHERF-1 in the physiological control of NHE3, we analyzed NHE3 activity in isolated brush border membrane (BBM) preparations from renal proximal tubules of wild-type (WT) and NHERF-1 (-/-) mice. Basal Na(+)-H(+) exchange was indistinguishable in BBMs from WT and NHERF-1 (-/-) mice (0.96+/-0.08 and 0.95+/-0.10 nmol/mg protein/10 s, respectively). Activation of membrane bound cAMP-dependent protein kinase (PKA) by cAMP inhibited NHE3 activity in WT BBMs (0.55+/-0.07 nmol/mg protein/10 s or 40+/-9%, P<0.01) but had no discernible effect on Na(+)-H(+) exchange in the NHERF-1 (-/-) BBM (0.97+/-0.07 nmol/mg protein/10 s; P=not significant). This was associated with a significant decrease in cAMP-stimulated phosphorylation of NHE3 immunoprecipitated from solubilized NHERF-1 (-/-) BBMs. As the protein levels for NHE3, NHERF-2, PKA and ezrin were not changed in the NHERF-1 (-/-) BBMs, the data suggest a unique role for NHERF-1 in cAMP-mediated inhibition of NHE3 activity in the renal proximal tubule of the mouse.     

Growth arrest and DNA damage-inducible protein GADD34 targets protein phosphatase 1 alpha to the endoplasmic reticulum and promotes dephosphorylation of the alpha subunit of eukaryotic translation initiation factor 2

The growth arrest and DNA damage-inducible protein, GADD34, associates with protein phosphatase 1 (PP1) and promotes in vitro dephosphorylation of the alpha subunit of eukaryotic translation initiation factor 2, (eIF-2 alpha). In this report, we show that the expression of human GADD34 in cultured cells reversed eIF-2 alpha phosphorylation induced by thapsigargin and tunicamycin, agents that promote protein unfolding in the endoplasmic reticulum (ER). GADD34 expression also reversed eIF-2 alpha phosphorylation induced by okadaic acid but not that induced by another phosphatase inhibitor, calyculin A (CA), which is a result consistent with PP1 being a component of the GADD34-assembled eIF-2 alpha phosphatase. Structure-function studies identified a bipartite C-terminal domain in GADD34 that encompassed a canonical PP1-binding motif, KVRF, and a novel RARA sequence, both of which were required for PP1 binding. N-terminal deletions of GADD34 established that while PP1 binding was necessary, it was not sufficient to promote eIF-2 alpha dephosphorylation in cells. Imaging of green fluorescent protein (GFP)-GADD34 proteins showed that the N-terminal 180 residues directed the localization of GADD34 at the ER and that GADD34 targeted the alpha isoform of PP1 to the ER. These data provide new insights into the mode of action of GADD34 in assembling an ER-associated eIF-2 alpha phosphatase that regulates protein translation in mammalian cells.     

On clustering in database servers for supporting mobile clients

The use of mobile computers is gaining popularity. There is an increasing trend in the number of users with laptops, PDAs, and smart phones. Access to information repositories in the future will be dominated by mobile clients rather than traditional “fixed” clients. These mobile clients download information by periodically connecting to repositories of data stored in either databases or file systems. Such mobile clients constitute a new and different kind of workload and exhibit a different access pattern than seen in traditional client server systems. Though file systems have been modified to handle clients that can download information, disconnect, and later reintegrate, databases have not been redesigned to accommodate mobile clients. There is a need to support mobile clients in the context of client server databases. This paper is about organizing the database server to take into consideration the access patterns of mobile clients. We propose the concept of hoard attributes which capture these access patterns. Three different techniques for organizing data on the server based on the hoard attribute are presented. We argue that each technique is suited for a particular workload. The workload is a combination of requests from mobile clients and traditional clients. This reorganization also allows us to address issues of concurrency control, disconnection and replica control in mobile databases. We present simulation results that show the performance of server reorganization using hoard attributes. We also provide an elaborate discussion of issues resulting from this reorganization in this new paradigm taking into account both mobile and traditional clients. This revised version was published online in August 2006 with corrections to the Cover Date.