Evaluation of the robustness of polarization attraction for 10.7-GBaud NRZ-BPSK after long-haul 100-GHz DWDM transmission

An investigation was carried out on the polarization attraction (PA) of a polarization-scrambled 10.7-GBaud NRZ-BPSK signal in a 1-km-long highly nonlinear fiber (HNLF). For the back-to-back case, PA on an ASE-loaded signal yielded a receiver sensitivity penalty of ≈ 14.5 dB at the ITU-T G.975.1.I3 FEC threshold of 3.5 × 10^-3, relative to matched-filter reception theory. After long-haul 100-GHz DWDM transmission in a recirculating loop, PA on the output signal was found to achieve approximately the same receiver sensitivity performance, as that of the back-to-back case. From these experiments, it is concluded that the Gordon-Mollenauer effect due to propagation in the HNLF during PA dominates other impairments including those arising from the long-haul 100-GHz DWDM recirculating loop transmission.

Polarization attraction of 10-Gb/s NRZ-BPSK signal in a highly nonlinear fiber

Polarization attraction of a 10-Gb/s non-return-to-zero binary phase-shift keyed (NRZ-BPSK) signal has been successfully demonstrated for the first time in a counter-propagating beam configuration using a continuous-wave pump, in a highly nonlinear fiber, by utilizing the Kerr nonlinear cross-polarization process inherent to that fiber. The efficacy of mitigating polarization-dependent loss across polarization-sensitive devices was emulated with a linear polarizer located before the receiver. The receiver sensitivity penalty at 10^-9 bit-error-rate relative to the baseline NRZ-BPSK signal was < 0.5 dB, when polarization attraction was employed for a polarization-scrambled signal (after achieving a degree of polarization > 90%). The results confirm that polarization attraction is independent of modulation format.

A Hospital-Based Interdisciplinary Model for Increasing Nurses' Engagement in Legislative Advocacy

The Legislative Action Interest Group (LAIG) is a hospital-based health policy forum that engages nurses in exploring clinical implications of existing and pending health policies and regulations, while also creating a feedback loop to inform policy makers about the realities nursing practice and patient care. The LAIG is a collaborative effort between the hospital's Department of Nursing and Patient Care Services and the Office of Government Relations at an academic children's hospital. Nurses participating in the LAIG forums build a working knowledge of health policy and can articulate the practice realities for policy decision makers. Participants explore the political context of nursing and pediatric policies while learning about the state legislative process. Beyond the monthly meetings, members build policy advocacy skills and have testified at public hearings, met with state and federal legislators, and led tours for policy makers through the hospital. The LAIG model also benefits the government relations staff by providing time for them to discuss clinical implications of pending policies with nurses from practice settings in the hospital. Forum discussions enhance the ability of the hospital's lobbyists to articulate practice implications of health policy to lawmakers. This case study, describing the origin, structure, operations, and outcomes of the LAIG model, and has implications for nurses in hospitals and academic settings who are interested in engaging in policy work. Opportunities to research the sustainability, replicability, and patient-centered outcomes of LAIG forums represent future work needed to advance nursing's participation in policy.

Polar auxin transport: controlling where and how much

Auxin is transported through plant tissues, moving from cell to cell in a unique polar manner. Polar auxin transport controls important growth and developmental processes in higher plants. Recent studies have identified several proteins that mediate polar auxin transport and have shown that some of these proteins are asymmetrically localized, paving the way for studies of the mechanisms that regulate auxin transport. New data indicate that reversible protein phosphorylation can control the amount of auxin transport, whereas protein secretion through Golgi-derived vesicles and interactions with the actin cytoskeleton might regulate the localization of auxin efflux complexes.

Genetic and chemical reductions in protein phosphatase activity alter auxin transport, gravity response, and lateral root growth

Auxin transport is required for important growth and developmental processes in plants, including gravity response and lateral root growth. Several lines of evidence suggest that reversible protein phosphorylation regulates auxin transport. Arabidopsis rcn1 mutant seedlings exhibit reduced protein phosphatase 2A activity and defects in differential cell elongation. Here we report that reduced phosphatase activity alters auxin transport and dependent physiological processes in the seedling root. Root basipetal transport was increased in rcn1 or phosphatase inhibitor-treated seedlings but showed normal sensitivity to the auxin transport inhibitor naphthylphthalamic acid (NPA). Phosphatase inhibition reduced root gravity response and delayed the establishment of differential auxin-induced gene expression across a gravity-stimulated root tip. An NPA treatment that reduced basipetal transport in rcn1 and cantharidin-treated wild-type plants also restored a normal gravity response and asymmetric auxin-induced gene expression, indicating that increased basipetal auxin transport impedes gravitropism. Increased auxin transport in rcn1 or phosphatase inhibitor-treated seedlings did not require the AGR1/EIR1/PIN2/WAV6 or AUX1 gene products. In contrast to basipetal transport, root acropetal transport was normal in phosphatase-inhibited seedlings in the absence of NPA, although it showed reduced NPA sensitivity. Lateral root growth also exhibited reduced NPA sensitivity in rcn1 seedlings, consistent with acropetal transport controlling lateral root growth. These results support the role of protein phosphorylation in regulating auxin transport and suggest that the acropetal and basipetal auxin transport streams are differentially regulated.

Genetic and chemical reductions in protein phosphatase activity alter auxin transport, gravity response, and lateral root growth

Auxin transport is required for important growth and developmental processes in plants, including gravity response and lateral root growth. Several lines of evidence suggest that reversible protein phosphorylation regulates auxin transport. Arabidopsis rcn1 mutant seedlings exhibit reduced protein phosphatase 2A activity and defects in differential cell elongation. Here we report that reduced phosphatase activity alters auxin transport and dependent physiological processes in the seedling root. Root basipetal transport was increased in rcn1 or phosphatase inhibitor-treated seedlings but showed normal sensitivity to the auxin transport inhibitor naphthylphthalamic acid (NPA). Phosphatase inhibition reduced root gravity response and delayed the establishment of differential auxin-induced gene expression across a gravity-stimulated root tip. An NPA treatment that reduced basipetal transport in rcn1 and cantharidin-treated wild-type plants also restored a normal gravity response and asymmetric auxin-induced gene expression, indicating that increased basipetal auxin transport impedes gravitropism. Increased auxin transport in rcn1 or phosphatase inhibitor-treated seedlings did not require the AGR1/EIR1/PIN2/WAV6 or AUX1 gene products. In contrast to basipetal transport, root acropetal transport was normal in phosphatase-inhibited seedlings in the absence of NPA, although it showed reduced NPA sensitivity. Lateral root growth also exhibited reduced NPA sensitivity in rcn1 seedlings, consistent with acropetal transport controlling lateral root growth. These results support the role of protein phosphorylation in regulating auxin transport and suggest that the acropetal and basipetal auxin transport streams are differentially regulated.

Genetic and chemical reductions in protein phosphatase activity alter auxin transport, gravity response, and lateral root growth

Auxin transport is required for important growth and developmental processes in plants, including gravity response and lateral root growth. Several lines of evidence suggest that reversible protein phosphorylation regulates auxin transport. Arabidopsis rcn1 mutant seedlings exhibit reduced protein phosphatase 2A activity and defects in differential cell elongation. Here we report that reduced phosphatase activity alters auxin transport and dependent physiological processes in the seedling root. Root basipetal transport was increased in rcn1 or phosphatase inhibitor-treated seedlings but showed normal sensitivity to the auxin transport inhibitor naphthylphthalamic acid (NPA). Phosphatase inhibition reduced root gravity response and delayed the establishment of differential auxin-induced gene expression across a gravity-stimulated root tip. An NPA treatment that reduced basipetal transport in rcn1 and cantharidin-treated wild-type plants also restored a normal gravity response and asymmetric auxin-induced gene expression, indicating that increased basipetal auxin transport impedes gravitropism. Increased auxin transport in rcn1 or phosphatase inhibitor-treated seedlings did not require the AGR1/EIR1/PIN2/WAV6 or AUX1 gene products. In contrast to basipetal transport, root acropetal transport was normal in phosphatase-inhibited seedlings in the absence of NPA, although it showed reduced NPA sensitivity. Lateral root growth also exhibited reduced NPA sensitivity in rcn1 seedlings, consistent with acropetal transport controlling lateral root growth. These results support the role of protein phosphorylation in regulating auxin transport and suggest that the acropetal and basipetal auxin transport streams are differentially regulated.

Phytobilin biosynthesis: the Synechocystis sp. PCC 6803 heme oxygenase-encoding ho1 gene complements a phytochrome-deficient Arabidopsis thalianna hy1 mutant

The phytobilin chromophores of phycobiliproteins and phytochromes are biosynthesized from heme in a pathway that begins with the opening of the tetrapyrrole macrocycle of protoheme to form biliverdin IXalpha, in a reaction catalyzed by heme oxygenase. An Arabidopsis thaliana hy1 mutant was previously shown to be deficient in phytochrome responses, and these responses were regained when the plants were administered biliverdin IXalpha. A heme oxygenase-encoding gene, ho1, was recently cloned from the cyanobacterium Synechocystis sp. PCC 6803. When ho1 was expressed in Escherichia coli, the cells produced active ferredoxin-dependent soluble heme oxygenase. The open reading frame of ho1 was fused in frame with a chloroplast transit peptide-encoding sequence from the oli gene of Antirrhinum majus. This construct was placed in a binary plasmid vectorcontaining a kanamycin resistance marker and a cauliflower mosaic virus 35S promoter to control expression of the chimeric oli-ho1 gene and used to transform A. thaliana hy1 plants. Two independent transformed lines were obtained that had the phenotype of the parental Landsberg erecta line and expressed the chimeric gene, as indicated by detection of its mRNA by reverse transcriptase-polymerase chain reaction. The results indicate that Synechocystis sp. PCC 6803 heme oxygenase encoded by ho1 can substitute for the defective HY1 gene product and that the only required enzyme activity of the HY1 gene product is heme oxygenase.

Functional expression of human and Arabidopsis protein phosphatase 2A in Saccharomyces cerevisiae and isolation of dominant-defective mutants

Protein phosphatase 2A (PP2A), a heterotrimeric serine/threonine-specific protein phosphatase, comprises a catalytic subunit and two distinct regulatory subunits, A and B. The primary sequence of the catalytic (C) subunit is highly conserved in evolution, and its function has been shown to be essential in yeast, Drosophila and mice. In many eukaryotes, the C subunit is encoded by at least two nearly identical genes, impeding conventional loss-of-function genetic analysis. We report here the development of a functional complementation assay in S. cerevisiae that has allowed us to isolate dominant-defective alleles of human and Arabidopsis C subunit genes. Wild-type human and Arabidopsis C subunit genes can complement the lethal phenotype of S. cerevisiae PP2A-C mutations. Site-directed mutagenesis was used to create two distinct, catalytically impaired C subunit mutants of the human and Arabidopsis genes. In both cases, expression of the mutant subunit in yeast prevented growth, even in the presence of functional C subunit proteins. This dominant growth defect is consistent with a dominant-interfering mode of action. Thus, we have shown that S. cerevisiae provides a rapid system for the functional analysis of heterologous PP2A genes, and that two mutations that abrogate phosphatase activity exhibit dominant-defective phenotypes in S. cerevisiae.

A mutation in protein phosphatase 2A regulatory subunit A affects auxin transport in Arabidopsis

The phytohormone auxin controls processes such as cell elongation, root hair development and root branching. Tropisms, growth curvatures triggered by gravity, light and touch, are also auxin-mediated responses. Auxin is synthesized in the shoot apex and transported through the stem, but the molecular mechanism of auxin transport is not well understood. Naphthylphthalamic acid (NPA) and other inhibitors of auxin transport block tropic curvature responses and inhibit root and shoot elongation. We have isolated a novel Arabidopsis thaliana mutant designated roots curl in NPA (rcn1). Mutant seedlings exhibit altered responses to NPA in root curling and hypocotyl elongation. Auxin efflux in mutant seedlings displays increased sensitivity to NPA. The rcn1 mutation was transferred-DNA (T-DNA) tagged and sequences flanking the T-DNA insert were cloned. Analysis of the RCN1 cDNA reveals that the T-DNA insertion disrupts a gene for the regulatory A subunit of protein phosphatase 2A (PP2A-A). The RCN1 gene rescues the rcn1 mutant phenotype and also complements the temperature-sensitive phenotype of the Saccharomyces cerevisiae PP2A-A mutation, tpd3-1. These data implicate protein phosphatase 2A in the regulation of auxin transport in Arabidopsis.

Sex determination gene TASSELSEED2 of maize encodes a short-chain alcohol dehydrogenase required for stage-specific floral organ abortion

Maize produces separate unisexual flowers through programmed abortion of preformed organ primordia. In the male inflorescence (tassel), stamen primordia develop to sexual maturity, while gynoecia (pistil primordia) are aborted. In tasselseed2 (ts2) mutant plants, floral structures in the tassel adopt a female developmental program. Here we report the transposon tagging and cloning of the TS2 gene, which plays a late but pivotal role in determining the sexual fate of floral meristems. Shortly before abortion of the gynoecium, Ts2 mRNA is expressed subepidermally in that primordium. Phenotypic instability of the Activator (Ac)-induced allele ts2-m1 indicates that late restoration of TS2 action in somatic tissues, which is correlated with Ac excision, reactivates the male developmental program. The predicted amino acid sequence of the Ts2 protein shows significant similarity to short-chain alcohol dehydrogenases, particularly hydroxysteroid dehydrogenases.

Trans-acting transposase mutant from Tn5

Transposition of Tn5 and of its component insertion sequence IS50R is regulated through the action of two proteins it encodes: a cis-acting transposase, Tnp, and a trans-acting inhibitor of transposition, Inh. The mechanism of the cis-acting Tnp and the relevance of inhibition to cis action have been addressed in the current study. A specific colony morphology assay for transposition of Tn5 was shown to be sensitive to Inh produced in trans and was used to screen for mutants in Inh and/or Tnp with altered regulation. A dominant mutant in IS50R that promotes transposition in trans was isolated and characterized. The mutant (449F) carries a Leu----Phe mutation at position 449 in Tnp. This mutation reduces the frequency of Tn5 or IS50R transposition in cis but allows Tnp-449F to act as efficiently in trans as it does in cis. Tnp-449F is sensitive to inhibition and, furthermore, Inh-449F is a competent inhibitor in trans. These results show that Tnp-449F is a trans-acting transposase, unlike wild-type Tnp, which is cis-acting.

Membrane association of the Tnp and Inh proteins of IS50R

Using a radioimmunoassay for the IS50R proteins Tnp and Inh, we found that both proteins were present primarily in the cytoplasm, but 3 to 11% of Tnp and 3 to 5% of Inh were found in association with the inner membrane. The fractions of total Tnp and Inh that became membrane bound were unaffected by the amount of Tnp and Inh synthesized in whole cells, provided that the ratio of total Tnp to total Inh was not changed. In addition, Inh was not found in the membrane fraction in Tnp- IS50R mutants, indicating that Tnp is required for Inh localization.

Disposition of a murine monoclonal antibody vinca conjugate (KS1/4-DAVLB) in patients with adenocarcinomas

The pharmacokinetics of a murine monoclonal antibody vinca conjugate (KS1/4-DAVLB) was investigated in 13 patients with adenocarcinomas who received single intravenous doses ranging from 40 to 250 mg/m2 and in three patients who were administered 1.5 mg/kg every 48 to 72 hours for up to 15 doses. Five patients in the single-dose study also received 100 microCi of [3H]-KS1/4-DAVLB. Overall mean values for the pharmacokinetic variables were as follows: elimination half-life, 31.5 hours; distribution volume, 4.43 L; and clearance, 0.09 L/hr. KS1/4-DAVLB demonstrated linear elimination kinetics in both the single- and multiple-dose studies. Significant concentrations of KS1/4-DAVLB were noted in a pleural effusion. Ten percent of the radioactive dose was recovered in the urine and 20% in the feces over a 5-day period. Small molecular weight vinca species were detected in the feces but not in the serum.

Escherichia coli nusB mutations that suppress nusA1 exhibit lambda N specificity

The bacteriophage lambda N protein regulates phage development by selectively suppressing transcription termination in its host, Escherichia coli. The E. coli nus mutants prevent N activity. To provide additional information on transcription termination, we have isolated pseudo-revertants of the nusA1 mutation that restore lambda N function. One series of pseudo-revertants lie in the E. coli nusB gene, whose product is normally required for lambda N activity. These mutations are N-specific: mutations that restore lambda N activity do not restore the activity of the analogous N protein of phage 21. Similarly, nusB mutations that restore phage 21 N function are deficient for lambda N function. Mapping of the two classes of mutation is consistent with their location in two distinct domains in the nusB protein. We discuss whether nusB is specific for N protein or for some other component of this regulation system, e.g. the phage site (nut) required for N action.