Spelling suggestions: "subject:"top own.""
141 |
Top-down eller bottom-up? : En kvalitativ studie om lärares val av läsinlärningsmetoder / Top-down or bottom-up? : A qualitative study on teachers choise of reading methodsNorén, Emma January 2017 (has links)
Syftet med undersökningen är att söka svar på hur yrkesverksamma lärare inom skolans tidi-gare åldrar åk.1–3 arbetar med läsinlärning. Jag vill även undersöka vilka läsinlärningsme-toder lärarna använder i undervisningen samt vilka faktorer som påverkat dessa lärares val av läsinlärningsmetoder. Min undersökning består av sex semistrukturerade kvalitativa intervjuer med lärare, all verksamma inom samma mellansvenska kommun. Flera intressanta aspekter har framkommit genom undersökningen. Bland annat att ingen av de intervjuade lärarna använder sig av en enda renodlad metod. Istället blandar de och tar ”det bästa” från olika metoder samt anpassar sitt arbetssätt delvis efter den barngrupp de arbe-tar med. Faktorer som påverkat lärarnas val av läsinlärningsmetoder är exempelvis trender, erfarna kollegor och kommunalt inflytande. / The aim of this study has been to find answers as to how primary teachers in the early ages (grades 1–3) help children in the process of learning to read. I also wanted to investigate wich methods teachers use in teaching their students in learning to read. My interest also lies in what has affected the teachers choice of reading methods. My study is based on six semistructured qualitative interviews with teachers, who all work in the same town, but in different schools. Several interesting aspects emerged from the interviews. For example, none of the teachers use only one reading method. The mix and match and adapt their teaching according to their class and preconditions. Factors that have influenced their choice of method is, among other things, trends older colleges and municipal influence.
|
142 |
Conséquences des interactions entre voies vertes et brunes sur la stabilité des réseaux trophiques / Consequences of interactions between green and brown paths on food web stabilityQuevreux, Pierre 12 September 2018 (has links)
Cette thèse a pour but de comprendre les implications des relations entre réseau trophique vert et réseau trophique brun sur la stabilité et le fonctionnement des réseaux trophiques. Les interactions entre ces deux réseaux, respectivement fondés sur la photosynthèse et la consommation de la matière organique morte, sont essentielles au fonctionnement des écosystèmes : l'un produit de la matière organique à partir de nutriments minéraux et l'autre recycle les nutriments contenus dans la matière organique morte. Cette question est abordée à l'aide de deux modèles théoriques et d'une étude expérimentale. Mon premier modèle montre que la boucle de rétroaction induite par le recyclage des nutriments dans un réseau trophique exclusivement vert a un effet stabilisant sur les dynamiques d'une chaîne trophique et un effet enrichissement à cause de la remise à disposition pour les producteurs primaires des nutriments excrétés par l'ensemble des organismes du réseau trophique. Cependant seul l'effet enrichissement, qui est déstabilisant, persiste dans un modèle de réseau trophique. Mon second modèle intègre le réseau brun de manière explicite et montre que ce réseau est davantage déstabilisé que le réseau vert lorsque la disponibilité en nutriments augmente. Cette effet est amplifié si la majeure partie de l'excrétion se fait sous forme de détritus qui déstabilisent le réseau brun par un effet d'enrichissement. Ce modèle montre également que la survie des consommateurs est améliorée lorsqu'ils peuvent consommer des proies provenant des deux réseaux. Mon expérience en mésocosmes aquatiques a permis d'étudier les effets en cascades entre réseaux vert et brun via une filtration de la lumière (manipulation directe du réseau vert), l'ajout de carbone organique dissous (manipulation directe du réseau brun) et l'ajout de poissons (manipulation de la structure du réseau trophique). Nous n'avons pas observé d'effets en cascade du réseau vert sur le réseau brun et inversement, notamment à cause d'un ajout probablement trop faible de carbone dissout. Les poissons ont eux eu un fort effet sur les deux réseaux avec des effets positifs sur le phytoplancton lorsque la lumière est réduite à cause de la diminution de la limitation par les nutriments grâce à l'excrétion des poissons, une augmentation de la concentration en carbone organique dissout et une modification du profil métabolique de la communauté bactérienne benthique. Un modèle annexe montre quant à lui que la plasticité du métabolisme chez les organismes, c'est-à-dire leur capacité à réduire ou à augmenter leur métabolisme en fonction de la disponibilité en ressources afin de maximiser leur bilan énergétique permet de stabiliser les dynamiques d'une chaine trophique en diminuant la variabilité temporelle des biomasses des espèces. Dans un réseau trophique, cette stabilisation se traduit par une augmentation de la persistance des espèces. Cette thèse a permis de mieux relier l'écologie des communautés à l'écologie fonctionnelle, améliorant ainsi notre compréhension des conséquences de grands processus écosystémiques comme le recyclage des nutriments sur la stabilité des réseaux trophiques et des effets de la structure de ces réseaux sur le fonctionnement des écosystèmes. / The aim of this thesis is to understand the implications of the relationships between green and brown food webs on the stability and functioning of food webs. The interactions between these two food webs, based respectively on photosynthesis and the consumption of dead organic matter, are essential for the functioning of ecosystems: one produces organic matter from mineral nutrients and the other one recycles the nutrients contained in dead organic matter. I address this by using two theoretical models and an experimental study. My first model shows that the feedback loop induced by nutrient cycling in an exclusively green food web has a stabilising effect on species dynamics in a food chain and an enrichment effect due to the excretion of nutrients that are available again for primary producers. However, only the enrichment effect, which is destabilising, persists in a food web model. My second model integrates a true brown food web and shows that this food web is more destabilised than the green food web when nutrient availability increases. This effect is amplified if most of nutrients are excreted as detritus that destabilises the brown food web through an enrichment effect. This model also shows that consumer survival is improved when they can consume prey from both green and brown food webs. My experiment in aquatic mesocosms enabled me to study the cascading effects between green and brown food webs thanks to light filtration (direct manipulation of the green food web), the addition of dissolved organic carbon (direct manipulation of the brown food web) and the addition of fish (manipulation of food web structure). We did not observe any cascading effects of the green food web on the brown food web and vice versa, probably because of a too low addition of dissolved carbon. The fish had a strong effect on both green and brown food webs with positive effects on phytoplankton when light is filtered because of the decreased nutrient limitation thanks to fish excretion, an increased concentration of dissolved organic carbon and a change in the metabolic profile of the benthic bacterial community. An additional model shows that the plasticity of metabolic rate, that is the ability of organisms to increase or decrease their metabolic rate depending on resource availability in order to optimise their energy budget, stabilises species dynamics in a food chain model by decreasing biomass time variability. Such a stabilising effect results in increase of species persistence in a complex food web model. This thesis is an additional step to better link community ecology to functional ecology, thus improving our understanding of the consequences on food web stability of major ecosystem processes such as the nutrient cycling and the effects of food web structure on ecosystem functioning.
|
143 |
Nahrungsnetzbewirtschaftung in MittelgebirgstalsperrenScharf, Wilfried 12 November 2004 (has links)
"Biomanipulation" was carried out in order to try and improve the water quality of six deep reservoirs situated in the catchment area of the River Wupper. All the reservoirs are deep, dimictic soft-water lake types, covering a range from oligo-/mesotrophic to eutrophic. Although changing the fishery management only by repeated fish stocking, in combination with implementating size and bag limits for recreational fisheries, is thought to have only limited success, we decided to put this type of "Biomanipulation" into practice. This whole-lake biomanipulation experiment, covering a time scale of more than ten years, aimed to address the following questions: 1. Is such a fishery-management strategy a useful water quality management tool in deep reservoirs, not only in maintaining but also in sustaining the best water quality conditions in relation to the given nutrient concentrations? 2. What are the underlying mechanisms? With the exception of the oligotrophic Große Dhünn Reservoir, "Biomanipulation" resulted in a shift of zooplankton body-size structure to larger daphnids in all the reservoirs. The underlying switch in the size shift from Daphnia cucullata to Daphnia galeata (Bever-Reservoir, Wupper-R, Lingese-R), or only in increasing individual body sizes of the Daphnia galeata population (Vorsperre Große Dhünn), occurred suddenly but only some years after the changes in fishery management were implemented. Our records of the fish stock suggest that indirect effects, presumably resulting from predator avoidance, must be a driving force. An increase of zooplankton body-size structure always resulted in an improvement in secchi-disk depth, often accompanied by a vertical restructuring of the water column favouring the development of metalimnetic algal populations. A decrease in summer chlorophyll concentrations in the trophogenic zone was only achieved in the slightly eutrophic reservoirs. This decrease in chlorophyll concentration was always accompanied by a decrease in the total phosphorus concentration in summer, while the total phosphorus concentration in spring remained unchanged. Thus, reduced P-availability, due to an increased vertical phosphorus flux, caused algal biomass to decline.These results support predictions from the size-efficiency hypothesis (Brooks & Dodson, 1965) but not those from the trophic cascade hypothesis (Carpenter et al., 1985). Undoubtedly the results underline the importance of indirect effects with respect to a successful "Biomanipulation" as predicted from the hypothesis of Biomanipulation Efficiency Threshold of P-loading (Benndorf, 1987). In summary, implementation of a correct fishery management strategy was shown to be a useful water quality management tool, not only in maintaining but also in sustaining the best water quality conditions, in relation to the given nutrient concentrations in these deep reservoirs. / In sechs Mittelgebirgstalsperren im Einzugsgebiet der Wupper erfolgte eine Umstellung der fischereilichen Bewirtschaftung mit dem Ziel, die Gewässergüte dieser Talsperren durch Absenkung der Zooplanktivorie zu verbessern und auf einem hohen Niveau zu stabilisieren. Vom Gewässercharakter her handelt es sich bei den Talsperren um klare tiefe Weichwasserseen, welche den oligo-/mesotrophen bis eutrophen Bereich abdecken. Die hier genutzte Methode einer ordnungsgemäßen fischereilichen Bewirtschaftung (Nahrungsnetzbewirtschaftung), welche sich zum Auf- und Umbau der Fischbestände auf Besatz- und Hegemaßnahmen stützt und dabei bewusst auf massive Eingriffe verzichtet, gelangte bisher nur in wenigen Fällen zur ausschließlichen Anwendung und wird allgemein als wenig erfolgversprechend eingestuft. Ziel dieser mehrjährigen Ökosystemuntersuchungen mit anwendungsorientiertem Ansatz ist eine Antwort auf die Frage nach der Praxistauglichkeit und den Grenzen des Instruments der Nahrungsnetzbewirtschaftung in Mittelgebirgstalsperren. Die Analyse der Ergebnisse versucht die zugrundeliegenden Mechanismen und Randbedingungen herauszuarbeiten, welche für die Wirkungsentfaltung der den Erfolg einer Nahrungsnetzbewirtschaftung tragenden Kräfte auf ökosystemarer Ebene verantwortlich sind. Mit Ausnahme der oligotrophen Großen Dhünn-Talsperre konnte in allen Gewässern eine adäquate Reaktion des Zooplanktons durch Umstellung der fischereilichen Bewirtschaftung erzielt werden. Im Einklang mit der Hypothese einer kritischen Schwelle der Planktivorie erfolgten die Reaktionen sprunghaft, aber erst nach mehreren Jahren und manifestieren sich durch einen "switch" von Daphnia cucullata zum größeren Daphnia galeata-Komplex (Bever-Talsperre, Wupper-T, Lingese-T), teils durch Körpergrößenzunahme des Daphnia galeata-Komplexes (Vorsperre Große Dhünn). Wie die Fischbestandsdaten nahe legen, kommt den indirekten, vermutlich aus einer Räuber-Vermeidungsreaktion resultierenden Effekten, hierbei eine Schlüsselposition zu. Parallel mit der Veränderung des Zooplankton-Größenspektrums kommt es stets zu einer Erhöhung der sommerlichen Sichttiefen, welche vielfach von einer vertikalen Neustrukturierung der Algenentwicklung im Wasserkörper begleitet ist. Eine Absenkung der sommerlichen Chlorophyll-Konzentrationen in der trophogenen konnte hingegen nur in den schwach eutrophen Talsperren beobachtet werden und war stets von einer erhöhten Absenkung der sommerlichen gegenüber den frühjährlichen Gesamtphosphor-Konzentrationen begleitet. Entsprechend muss die Absenkung der sommerlichen Chlorophyll-Konzentrationen auf eine erhöhte Phosphor-Sedimentation zurückgeführt werden.Die Ergebnisse der fischereilichen Bewirtschaftungsmaßnahmen stehen im Einklang mit den Vorhersagen der size-efficiency Hypothese (Brooks & Dodson, 1965), stützen aber nicht die Vorhersagen der trophic cascade Hypothese (Carpenter et al., 1985). Demgegenüber unterstreichen sie die Bedeutung indirekter Effekte, wie sie durch die These einer "Biomanipulationseffektivitätsschwelle der Phosphor-Belastung" (Benndorf, 1987) formuliert werden. Insgesamt erweist sich das Instrument der Nahrungsnetzbewirtschaftung als zwingender Baustein einer integrierten Wasserwirtschaft zur Sicherung der Gewässergüte in Mittelgebirgstalsperren, dessen soziökonomische Aspekte in der Arbeit angesprochen werden.
|
144 |
Evropeizace měst v České republice / Europeanisation of municipalities in the Czech RepublicSchacherlová, Sylva January 2021 (has links)
The diploma thesis Europeanisation of Municipalities in the Czech Republic deals with the effects of membership in the European Union on the administrative structures of selected municipalities. This is a comparative case study of municipalities of various sizes and significance, namely the capital city of Prague, the statutory city of Pilsen and the city with extended powers Pisek. The aim of the thesis is to clarify which institutions in these municipalities manage the European agenda. The thesis follows three dimensions of the concept of Europeanisation (top-down; bottom-up and horizontal), which allows us to observe this issue from different angles. Research questions follow the logic of these three dimensions and the last research question focuses on comparing the Europeanisation of selected municipalities and identifying differences based on their size. The main source of the information was interviews with officials and politicians responsible for the European agenda in selected municipalities. The results of the work confirm the theoretical assumption that the size of municipalities has a significant impact on the management of the EU agenda. Financial and administrative capacities, the setting of European funds for the given city and the opinions of local political elites play the role...
|
145 |
Deterministic Silicon Pillar Assemblies and their Photonic ApplicationsDev Choudhury, Bikash January 2016 (has links)
It is of paramount importance to our society that the environment, life style, science and amusement flourish together in a balanced way. Some trends in this direction are the increased utilization of renewable energy, like solar photovoltaics; better health care products, for example advanced biosensors; high definition TV or high resolution cameras; and novel scientific tools for better understanding of scientific observations. Advancement of micro and nanotechnologies has directly and positively impacted our stance in these application domains; one example is that of vertical periodic or aperiodic nano or micro pillar assemblies which have attracted significant research and industrial interest in recent years. In particular, Si pillars are very attractive due to the versatility of silicon. There are many potential applications of Si nanopillar/nanowire assemblies ranging from light emission, solar cells, antireflection, sensing and nonlinear optical effects. Compared to bulk, Si pillars or their assemblies have several unique properties, such as high surface to volume ratios, light localization, efficient light guiding, better light absorption, selective band of light propagation etc. The focus of the thesis is on the fabrication of Si pillar assemblies and hierarchical ZnO nanowires on Si micro structures in top-down and bottom-up approaches and their optical properties and different applications. Here, we have investigated periodic and aperiodic Si nano and micro structure assemblies and their properties, such as light propagation, localization, and selective guiding and light-matter interaction. These properties are exploited in a few important optoelectronic/photonic applications, such as optical biosensors, broad-band anti-reflection, radial-junction solar cells, second harmonic generation and color filters. We achieved a low average reflectivity of ~ 2.5 % with the periodic Si micropyramid-ZnO NWs hierarchical arrays. Tenfold enhancement in Raman intensity is also observed in these structures compared to planar Si. These Si microstructure-ZnO NW hierarchical structures can enhance the performance and versatility of photovoltaic devices and optical sensors. A convenient top-down fabrication of radial junction nanopillar solar cell using spin-on doping and rapid thermal annealing process is presented. Broad band suppressed reflection, on average 5%, in 300- 850 nm wavelength range and an un-optimized cell efficiency of 6.2 % are achieved. Our method can lead to a simple and low cost process for high efficiency radial junction nanopillar solar cell fabrication. Silicon dioxide (SiO2) coated silicon nanopillar (NP) arrays are demonstrated for surface sensitive optical biosensing. Bovine serum albumin (BSA)/anti-BSA model system is used for biosensing trials by photo-spectrometry in reflection mode. Best sensitivity in terms of limit of detection of 5.2 ng/ml is determined for our nanopillar biosensor. These results are promising for surface sensitive biosensors and the technology allows integration in the CMOS platform. Si pillar arrays used for surface second harmonic generation (SHG) experiments are shown to have a strong dependence of the SHG intensity on the pillar geometry. The surface SHG can be suitable for nonlinear silicon photonics, surface/interface studies and optical sensing. Aperiodic Si nanopillar assemblies in PDMS matrix are demonstrated for efficient color filtering in transmission mode. These assemblies are designed using the ‘‘molecular dynamics-collision between hard sphere’’ algorithm. The designed structure is modeled in a 3D finite difference time domain (FDTD) simulation tool for optimization of color filtering properties. Transverse localization effect of light in our nanopillar color filter structures is investigated theoretically and the results are very promising to achieve image sensors with high pixel densities (~1 µm) and low crosstalk. The developed color filter is applicable as a stand-alone filter for visible color in its present form and can be adapted for displays, imaging, smart windows and aesthetic applications. / <p>QC 20160407</p>
|
146 |
Sport and the multisectoral approach to HIV/AIDS in ZambiaBanda, Davies January 2013 (has links)
Sport is increasingly being recognised for the contribution it can make to the Millennium Development Goals and, in particular, the response to the HIV/AIDS pandemic. This study is based on Zambia, a low-income country, heavily affected by the HIV/AIDS pandemic in sub-Saharan Africa. The study focuses on National Sports Associations (NSAs), which are quasi- autonomous organisations at meso level of policy analysis. Centring on three NSAs: Football Association of Zambia (FAZ), Zambia Basketball Association (ZBA) and Netball Association of Zambia (NAZ), this study critically analysed the organisational responses of each of the selected cases towards the HIV/AIDS multisectoral approach. The study adopted a case study approach which utilised semi-structured (face-to-face and telephone), interviews, focus group discussions and documentary analysis for data collection. Comparative analysis of all three cases revealed differences in how each case mainstreamed HIV/AIDS based on power, resources and forms of collaboration. Meso-level analysis was utilised to examine workplace HIV/AIDS policy formulation and implementation. In addition, meso-level analysis also helped reveal forms of health-related collaborations with both internal and external agencies. Macro-level theories of the state were useful in examining power relations between the Zambian state and civil society. The application of policy network theory, global health governance, multiple streams framework, and the top-down and bottom-up approaches to policy implementation proved useful in drawing attention to how each NSA case responded differently to the mainstreaming of HIV/AIDS. The political power of football as a national sport and the Association s access to foreign resources enabled FAZ to influence HIV/AIDS policy implementation and build of strong collaborative relationships with government than the ZBA and NAZ. The study concludes that lack of political steer from the top has re-introduced a new foreign top-down approach as those with resources from the Global North influenced policy formulation and implementation within all three cases. The conclusion also found useful the application of post-colonialism and development theories when examining international sport-for-development practices. This finding revealed the power imbalances between Global South practitioners and Global North funding partners.
|
147 |
Political culture and socialisation responses to integrated water resources management (IWRM) : the case of Thabo Mofutsanyane District Municipality / Sysman MotloungMotloung, Sysman January 2010 (has links)
This study looks at political culture and socialisation responses to Integrated Water Resource Management (IWRM). It identifies political culture and socialisation as part of a process, the development of a political culture with specific attitudes, cognitions, and feelings towards the political system. Political culture and socialisation impart the knowledge of how to act politically, i.e. how to apply values in formulating demands and making claims on the political system. They form a connecting link between micro- and
macro-politics. The study maintains that political orientations are handed down from one generation to another, through the process of political socialisation. Top-down and bottom-up influences come into play to augment a discourse on the global nature of political socialisation and the political culture of international societies with regard to IWRM and governance ideologies. It is argued that these international ideas become relevant in the
national political agenda, civil society organisations and trans-national networks. The IWRM aspects of water as an economic good and a basic human right have become a two-edged sword in the South African context. The study reveals that politics stand at the epicentre of water problems, and that IWRM is a political-ethical issue which challenges power bases in many communities. The IWRM global norms of equitable, efficient and sustainable use of water resources have become a major problem in a water-scarce country burdened with economic inequalities and abject poverty. This is a pressing issue because there is an increasing demand for water to sustain the development necessary to redress the draconian ills of the apartheid past. This becomes evident in the fundamental legislative overhaul that has taken place since 1994, embracing a transformation culture that glorifies the norm of water not only as a fundamental human right, but also as a commodity that is necessary to sustain human dignity. It is here that water is politicised. Violent protests have erupted in reaction to perceived neo-liberal attempts to deny the poor their access to this resource. The political culture and socialisation responses as far as IWRM is concerned appear within fragmented lines, i.e. mainly black and poor communities embrace a culture of non-payment for services and resort to violent protests as a viable method to raise their
concerns. In contrast, the white and middle-class communities manifest a tendency to form parallel local government structures; they then withhold rate payments and provide services for themselves through ratepayer associations. Finally, the study considers the South African context with regard to the manifestations of political culture, and how this influences water resources. It is evident that there is too much emphasis on politics at the expense of
discussions on IWRM. Civil society organisations make very little attempt to encourage public participation in water management structures. It also appears that political elites who are disillusioned with civil society organisations tend to derail their efforts to educate the public on water management structures. / MA, Political Studies, North-West University, Vaal Triangle Campus, 2011
|
148 |
Visual Attentional Capture Resists Modulation in Singleton Search under Verbal Working Memory LoadJohansson, Martin January 2016 (has links)
Visual attentional capture is a form of visual attentional selection that is automatic and involuntary in nature, and is of high adaptive value as it allows visual attention to be oriented in a reflexive manner towards visual information without necessarily being guided by pre-existing knowledge, goals, and plans. According to the load-hypothesis (Lavie & De Fockert, 2005), attentional capture of salient stimuli increases under load on working memory due to disruption of stimulus-processing priorities. Moreover, it has been proposed that maintenance of task-irrelevant verbal information increases distractor interference in singleton search by increasing attentional capture of salient, but task-irrelevant, color singletons. This hypothesis was tested in the present study by having participants complete several succeeding trials of singleton search while simultaneously maintaining digits in working memory. The presence of task-irrelevant color singletons in the search array of a singleton search task led to increased response times, indicating attentional capture. However, the cost to response times associated with distractor presence did not increase under load on working memory, indicating that distractor interference may not be affected by load on working memory when task-irrelevant verbal information is maintained over an extended period of time. Individual differences in action video game playing and trait anxiety were considered and excluded as possible confounders.
|
149 |
Top-down attention: neural pathways in the human and non-human primate examined by electrophysiology, optogenetics and psychophysicsHüer, Janina 08 February 2018 (has links)
No description available.
|
150 |
Placental ‘Omics’ Study to Understand the Pathogenesis of PreeclampsiaKedia, Komal 01 May 2016 (has links)
Preeclampsia (PE) is a potentially fatal complication of pregnancy characterized by an increase in blood pressure (>140/90 mmHg) and proteinuria (>300 mg/24 hrs), often accompanied by edema. Symptoms of PE start after 20 weeks of gestation. If PE remains untreated, it can lead to eclampsia, grand-mal seizures responsible for most fatalities. PE is believed to affect 2-10% of pregnancies worldwide, and claims the lives of over 75,000 mothers and 500,000 newborns yearly. No therapeutic agents have been developed to prevent or cure PE. Part of the reason for this is the absence of a complete understanding of the pathogenesis of this disease. PE has long been regarded as a “disease of theories”, and the pathophysiology of PE continues to be the subject of debate. Nonetheless, several abnormalities have been observed to precede established, clinical PE and have in turn been proposed to be involved in the causation of this disease, all with involvement of the mother's placenta as a central feature. Removal of placenta is the only cure for PE and results in a rapid resolution of the symptoms. Thus, the placenta remains an organ of substantial interest and many research groups have attempted to identify abnormal placental features occurring in PE. None of these studies have focused on less abundant, low molecular weight (LMW) biomolecules, which play important roles in the pathophysiology of many diseases. There are a number of alterations that are believed to affect the placenta and contribute to the pathogenesis of PE. The most widely accepted ones include hypoxia, oxidative stress, and an increase of pro-inflammatory mediators in the mother's placenta. The goal of my initial study was to identify which of these hypothesized causative pathways has a significance in the etiology of this syndrome as well as to investigate which less abundant, low molecular weight biomolecules change in response to these abnormalities. For this purpose, we first adapted and optimized a previously developed methodology that studied LMW biomolecules in tissue specimens to study placental biomolecules. This approach involved a tissue homogenization step followed by protein depletion using acetonitrile. We compared two regions of human placenta: the chorionic plate and the basal plate to find differences in the LMW fraction. We discovered 16 species with statistically significant differences between the two sides, and identified 12 of them using tandem mass spectrometry. In the second study we collected normal human term placentas from elective C-section deliveries and exposed explants to each of the above-mentioned provocative agents or stress conditions for 48 hrs. Other explants without any stressors were cultured in parallel for the same amount of time. The processing of explants was divided into five steps: 1) explant culture; 2) tissue homogenization; 3) acetonitrile precipitation to remove high abundance, high molecular weight proteins; 4) injection of the protein-depleted specimen into a capillary liquid chromatography–mass spectrometer; 5) analysis of MS data to identify quantitative differences between cases (stressed explants) and controls (normal explants). In total, we observed 146 molecules changed in abundance between the treated explants and the controls with 75 of these molecules changed in response to hypoxic treatment, 23 changed due to hypoxia-reoxygenation, a process generating reactive oxygen species, and 48 changed due to tumor necrosis factor–alpha (TNFα), a pro-inflammatory cytokine. We were successful in identifying 45% of all these molecules by tandem MS. Statistical modeling that applied LASSO analysis allowed for the development of a model that used 16 of the 146 differentially expressed biomolecules to accurately classify and differentiate each of the 4 stressed conditions. In my third study, I then submitted actual preeclamptic and non-diseased placental tissue to our established homogenization and acetonitrile precipitation protocol to see if any of the differences in LMW biomolecules produced under stress conditions in normal placenta were recapitulated in actual diseased placenta. In a preliminary statistical analysis, 8 of the original 146 differentially expressed species, displayed significant or near significant changes in the actual disease placenta. After applying two stringent statistical tests that eliminated any potential influence of gestational age, four out of the 146 biomarkers previously studied, continued to be differentially expressed in both stringent analyses. Of the four, 1 biomarker (m/z 649.49 (+1)) showed an increased abundance in hypoxic placental explants as well as in PE placenta; 2 (461.06 (+1), 476.24 (+1)) were increased in response to TNFα-exposed placental explants and in these PE placentas and 1 (426.35 (+1)) increased in response to hypoxia-reoxygenation-treated placental explants was also increased in PE placenta. We have chemically characterized 2 of the 4 biomarkers. One was a phospholipid (m/z 476.24) while the other was an acyl-carnitine (m/z 426.35). This suggests that features of PE appear to arise from the predicted early abnormalities that affect the placenta. In conclusion, I was successful in developing an ‘omics’ approach to study less abundant, low molecular weight biomolecules in human placenta as well as investigate which biomarkers show differential expression in human placenta when exposed to proposed abnormalities of PE and have data to suggest that these same responses are present in PE placenta.
|
Page generated in 0.2325 seconds