La salinité du sol affecte la croissance des plantes glycophytes telle que Arabidopsis thaliana et le riz. Chez les plantes vasculaires, les racines sont composées de divers types de cellules organisées en cercles concentriques. Chaque type de cellules racinaires possède une fonction biologique spécifique et coordonnée avec les autres cellules qui composent cette même racine. Il est probable que la réponse des gènes au stress salin soit spécifique du type cellulaire, ce qui ne peut être révélé par des études à l'échelle de l'organe entier. Afin d'étudier les réponses spécifiques, notre approche a été de générer des profils de transcriptome pour deux types de cellules racinaires chez les plantes modèles, Arabidopsis et riz. Les deux types de cellules étudiées ont été choisis en raison de leur rôle possible soit dans le stockage du sodium dans les cellules corticales, soit dans son transport dans les cellules du péricycle chez Arabidopsis ou du cylindre central chez le riz. Des plantes exprimant la protéine fluorescente verte (GF) spécifiquement dans un type de cellule racinaire furent utilisées pour cette analyse. Les cellules ont donc pu être isolées chez le riz et Arabidopsis grâce à la technique de cytométrie en flux.L'analyse du transcriptome des cellules du péricycle et du cylindre central montrent que les cellules corticales sont plus réactives au stress salin et qu'une large majorité des gènes est sous–exprimée chez les deux plantes modèles. D'après les analyses d'expression des cellules du cortex d'Arabidopsis, trois voies métaboliques sont significativement sous-exprimées en réponse au stress salin: la voie de biosynthèse des phénylpropanoïdes, le transport de l'eau and le métabolisme secondaire. La régulation de gènes impliqués dans le transport de l'eau et des nutriments démontre l'importance des cellules corticales dans le mouvement des solutés. Chez le riz, les profils des deux types cellulaires étudiés révèlent une forte réaction de défense ; en effet le métabolisme protéique et la régulation de la transcription sont fortement sous-exprimés dans les cellules corticales alors que les cellules du cylindre central modifient et activent les gènes correspondant à divers catégories fonctionnelles telles que la réplication de l'ADN et le transport. Des gènes candidats ont été sélectionnés dans les deux types cellulaires d'Arabidopsis. Des lignées mutantes n'exprimant pas ces gènes ont été testées en stress salin dans des conditions hydroponiques. Les résultats ont révélé un phénotype accumulant moins de sodium dans les parties aériennes (20% par rapport au génotype sauvage) pour certaines de ces lignées mutantes. Ce travail est la première étude de transcriptome utilisant des types spécifiques de cellules racinaires chez le riz. L'identification de gènes et voies métaboliques répondant au stress salin dans le cortex et le cylindre central de la racine ouvre de nouveaux axes de recherche et va permettre d'élucider la complexité des processus biologiques d'adaptation au stress salin. / Soil salinity reduces the growth of glycophytic plants such as Arabidopsis thaliana and rice. In vascular plants, roots are organized into concentric layers of cells and each layer has a specific biological function coordinated with other cell types in the root. Therefore, genes differentially expressed in response to a salt stress are also likely to be changing only in specific cell types, and thus may not be revealed at the organ level. In order to identify novel salt-responsive genes, cell-type specific transcriptomic approaches were undertaken in Arabidopsis thaliana and rice, with application of physiologically reasonable salt stress (50mM) over 48 hours. Two cell-types from the root were chosen in both species for their potential role in salt storage and transport: cortical and pericycle/stelar cells respectively. Cell-types of interest expressing specifically Green Fluorescent Protein (GFP) were isolated from the rest of the root using fluorescence-activated cell sorting (FACS).The outer layer of the root was found to be responding more than the inner part of the root after 48 hours of salt stress, with an overall down-regulation in both rice and Arabidopsis. Arabidopsis cortical cells responding to salt seem to regulate the cell wall biosynthesis, which may modulate the shape of the cells or alter the apoplastic movements of solutes in response to salt. Genes related to transport were affected by salt in Arabidopsis, with the crucial role of cortical cells in the movement of solutes being evident. Rice cortical cells respond to salt by showing a more extreme defence reaction in changing the protein metabolism and the regulation of transcription. The response of the inner part of the rice root to 48 hours of mild salt stress showed up-regulation of genes implicated in broader functional categories. The biological relevance of genes revealed using cell-type specific transcriptomics was demonstrated in a salt assay using knock-out (KO) lines of candidate genes from both cell-types in Arabidopsis thaliana. Three KO mutant lines showed 20% reduction in shoot sodium after 5 weeks of salt stress and were also able to maintain a higher shoot dry weight. These transcriptomic studies of isolated stelar and cortical cells in response to a mild salt stress have revealed salt responsive genes and pathways, indicating new areas for further study, and contributing to our understanding of the complex responses of plants to their environment at the cellular level.

Doctor of Philosophy / Entomology / Yoonseong Park / Tick salivary secretion is crucial for survival and for successful feeding. Tick saliva includes excretory water/ions and bioactive components for compromising the hosts' immune responses, and provides a direct route for pathogen transmission. Control of the tick salivation involves autocrine/paracrine dopamine, the most potent stimulator of tick salivation. Our research group reported the presence of two dopamine receptors in the salivary glands of the blacklegged tick (Ixodes scapularis): dopamine receptor (D1) and invertebrate specific D1-like dopamine receptor (InvD1L). Dopamine-induced salivary secretion was orchestrated by two distinct physiological roles via activation of the two dopamine receptors (Chapter 2). Low concentration of dopamine activated D1 receptor on epithelial cells of salivary gland acini leading inward fluid transport. High concentration of dopamine activated InvD1L receptors on axonal projections innervating myoepithelial cells modulating pumping/gating actions for emptying luminal saliva into the main duct. Thus, ticks coordinated salivary secretion with duo dopamine receptors. Dopamine-mediated saliva production involves an important downstream component, Na/K-ATPase (Chapter 3). Na/K-ATPase was found in the epithelial cells of all types of acini. However, Na/K-ATPase had two different functions in salivary secretion in different acini: 1) dopamine-mediated production of primary saliva in distally located salivary gland acini type-2/- 3, and 2) dopamine-independent resorption in proximally located salivary gland acini type-1. Type-1 acini were also found to function in direct water absorption of off-host ticks, which could be a potential route for delivery of acaricides. Chapter 4 investigated the comparative transcriptomics of the lone star tick underlying the processes of pathogen acquisition. Differential expression analyses in pathogen-exposed ticks revealed a number of transcripts that are important in the tick-pathogen interaction. These included genes for tick immunity against pathogen and for modulation of tick physiology facilitating a pathogen’s invasion and proliferation. My study expanded the understanding of physiological mechanisms controlling tick salivation. In addition, transcriptomics of ticks in interaction with pathogen identified several genes that are relevant in vector/pathogen interactions. The knowledge obtained in my study will facilitate to the development of novel methods for the disruption of tick feeding and pathogen transmission.

The aim of this thesis is to in various ways explore protein expression in human normal tissue and in cancer and to apply that knowledge in biomarker discovery. In Paper I the prognostic significance of RNA-binding motif protein 3 (RBM3) is explored in malignant melanoma. To further evaluate the prognostic significance of RBM3 expression was assessed in 226 incident cases of malignant melanoma from the prospective populationbased cohort study Malmö Diet and Cancer Study using tissue microarray technique (TMA). RBM3 was shown to be down regulated in metastatic melanoma and high nuclear expression in the primary tumor was an independent marker of prolonged over all survival. As a tool to facilitate clinical biomarker studies the Human Protein Atlas has created a tissue dictionary as an introduction to human histology and histopathology. In Paper II this work is introduced. A cancer diagnosis can be a complex process with difficulties of establishing tumor type in localized disease or organ of origin in generalized disease. Immunohistochemically assisted diagnosis of cancer is common practice among pathologists where its application combined with known protein expression profiles of different cancer types, can strengthen or help dismiss a suspected diagnosis. In Paper III the diagnostic performance of 27 commonly used antibodies are tested in a predominantly metastatic, multicancer cohort using TMA technique. Overall these 27 diagnostic markers showed a low sensitivity and specificity for its intended use, highlighting the need for novel, more specific markers. Breast, ovarian, endometrial and ovarian cancers affect predominantly women. Differential diagnostics between these cancer types can be challenging. In Paper IV an algorithm, based on six different IHC markers, to differentiate between these cancer types is presented. A new diagnostic marker for breast cancer, namely ZAG is also introduced. In Paper V the transcriptomic landscape of the adrenal gland is explored by combining a transcriptomic approach with a immunohistochemistry based proteomic approach. In the adrenal gland we were able to detect 253 genes with an elevated pattern of expression in the adrenal gland, as compared to 31 other normal human tissue types analyzed. This combination of a transcriptomic and immunohistochemical approach provides a foundation for a deeper understanding of the adrenal glands function and physiology.

Transcriptomics is the large-scale study of RNA molecules produced by the genome, in single cells or population of cells using high-throughput methods. With the advances in transcriptomic analysis, the monitoring of genome-wide gene expression provides a powerful approach for determining the action of drugs. In this study, we analyzed the transcriptional responses of cells treated with drugs either alone or in combinations to explore their effects in two different applications: breast cancer therapy and cell conversion. In the first part of this thesis, we aim at modeling the relationship between single and multidrug breast therapy at the transcriptome level. We monitored the effects of three drugs, and their combinations in human breast cancer MCF-7 cells using the cap analysis of gene expression method. We are the first to explore the impact of single and combinatorial treatment on promoter and enhancer expression on a genome-wide scale. After applying and customizing a broad spectrum of regression algorithms, we showed that the transcriptional response to combinatorial drug treatment at both promoters and enhancers is accurately described by a linear combination of the responses to the individual drugs. Our analysis is promising for eliciting the transcriptional reaction to multidrug therapies in an unbiased genome-wide way, which may minimize the need for exhaustive combinatorial screens. Following the drug combination analysis, we explored the possibility to systematically identify drugs that either alone or in combinations facilitate cell conversion. To date, no computational approach prioritizes or suggests chemical compounds promoting cell reprogramming. Using transcriptomic data of human primary cells and drug response expression profiles, we developed a computational framework which accurately predicts single drugs or drug cocktails driving any source cell type towards the desired lineage. Experimental and in-silico validation on human pluripotent stem cells confirms the ability of the top predicted drugs to enhance reprogramming. The introduced method has countless applications in regenerative medicine and can significantly speed up the research in this field.

Pour enrichir les connaissances scientifiques sur les effets biologiques des radionucléides et risques des contaminations chroniques sur la descendance, une étude multigénérationnelle in vivo d’exposition a été réalisée à doses non toxiques d'uranium. Ce modèle, a permis de suivre les effets biologiques de l’uranium sur trois générations de rats (F0, F1 et F2) par des analyses cliniques et le suivi de marqueurs biologiques. Dans cette étude, des analyses métabolomiques, transcriptomiques et épigénomiques ont été réalisées à partir d’échantillons de sang, d’urine et de rein.Pour la première génération des rats contaminés (F0), des différences dépendant du sexe des animaux sont observables par l’analyse des niveaux d’expression géniques (ARNm et micro-ARN) dans les reins, des profils métabolomiques et biochimiques dans les reins, l’urine et le sang. Aucune modification épigénétique des profils de méthylation de l’ADN rénal n’est à noter. Pour les deux générations suivantes (F1 et F2), un effet multigénérationnel dépendant aussi du sexe des rats est observable au niveau des profils métabolomiques urinaires et rénaux ainsi qu’au niveau des profils épigénétiques de méthylation de l'ADN des reins. Une baisse de poids corporel et des reins a aussi été observée pour la troisième génération de rats chez les mâles (F2).En conclusion, les travaux de cette thèse montrent qu’une contamination chronique à faible dose d'uranium entraine des effets biologiques sur plusieurs générations de rats. Ils sont observables à différents niveaux moléculaires des systèmes de régulation cellulaires et dépendent du sexe des rats. Ces effets, étroitement liés à des systèmes biologiques intégrés, sont utiles à la compréhension des mécanismes biologiques des expositions à l'uranium et à l’évaluation des risques de nocivités à long termes. Dans le domaine de la radioprotection, ces résultats justifient la nécessité de considérer les dimorphismes sexuels des individus et les conséquences des expositions sur les générations à venir. / In order to deepen scientific knowledge regarding biological effects of radionuclides and associated risk to offspring, an in vivo multigenerational study of chronic exposure to a non-toxic dose of uranium was performed by monitoring three generation of rats (F0, F1 and F2). Clinical parameters and biological markers, including metabolomics, transcriptomics and epigenomics high throughput analysis were conducted in blood, urine and kidney samples.For the first generation of contaminated rats (F0) sex-differences to uranium effects were observed in kidney for gene expression (mRNA, miRNA) and in kidney, urine and blood for biochemical parameters and metabolomics profiles. No epigenetic modification of DNA methylation profiles was shown in kidney. For the next two generations (F1, F2), a multigenerational sex-specific effect is observed for both metabolomics and renal DNA methylation profiles of contaminated rats. Moreover, for the last generation of male rats (F2), a decrease of both total body and kidney weight was shown.In conclusion, low-dose chronic contamination of rats to uranium leads to multigenerational effects. Including sex-differences, they can be shown at different molecular levels of the cellular system. Depending of integrated system biology, data of this thesis are useful in the understanding of biological mechanisms of uranium effect and risk of delayed harmful effect. In the field of radiation protection, these results prove the requirement of considering sexual dimorphisms and consequences of such exposures to offspring.

Thousands of chemical pollutants enter the environment continuously, each with the potential to cause adverse effects in both terrestrial and aquatic organisms. As a result, organisms are often exposed to a mixture of stressors within their habitat. Populations of fish inhabiting most aquatic environments are exposed to time-varying or repeated pulses of exposure, driven by run-off events or spills, or due to their mobility between polluted and clean waters. Therefore, the sustainability of fish populations is critically dependent on their ability to adapt to frequent changes in their local environment. Despite this, legislation to protect the environment from chemical contamination are generally based on toxicological measurements following exposures to single stressors, conducted under optimal laboratory conditions, and that do not take into account the variation in susceptibility of wild populations, or the potential consequences of exposure for the susceptibility of the population during future exposures, including across generations. Increasing evidence is suggesting that a number of chemicals may interact with the epigenome, and that differential responses to pollutants may be modulated, at least in part, via epigenetic mechanisms. However, our understanding of the role of epigenetic mechanisms in normal development in fish models or its susceptibility to exposure to environmental stressors is currently very limited. This thesis aimed to document the mechanisms of genetic and epigenetic responses to industrial pollutants in fish, and to explore the extent to which differential responses can be induced in the lab following exposure during the critical window of embryonic development or in adults. To address these objectives, I performed a series of experiments using both the zebrafish (Danio rerio) and the three-spined stickleback (Gasterosteus aculeatus) as fish models. I first used the zebrafish (Danio rerio) model to investigate the sex-specific transcription and DNA methylation profiles for genes involved in the regulation of reproduction and in epigenetic signalling in the livers and gonads. I provide evidence of the sex-specific transcription of genes involved in reproduction and their regulation by epigenetic signalling in this commonly used vertebrate model and highlight important considerations regarding the use of whole tissues comprised of multiple cell types in epigenetic and transcriptomic studies. I then investigated the potential for exposure to Bisphenol A (BPA) to cause adverse effects on reproduction and to disrupt the expression profiles and promotor DNA methylation of target genes important for reproductive function and epigenetic signalling in the zebrafish. To do this, I exposed breeding zebrafish to a range of BPA concentrations over 15 days and found that BPA disrupted reproductive processes in zebrafish, likely via estrogenic mechanisms, but only at high concentrations. Importantly, exposure to environmentally relevant concentrations of BPA resulted in altered transcription of key enzymes involved in DNA methylation maintenance, and caused changes in promoter DNA methylation. I also conducted a series of repeated exposures to copper in the three-spined stickleback to investigate the extent to which differential susceptibility can be induced in the lab. This work provides evidence that pre-exposure to copper results in differential responses in future exposure scenarios both when the initial exposure occurred in adults and during embryogenesis. For adults, fish appeared to recover completely from the initial exposure following a period of depuration of 30 days, but displayed decreased susceptibility upon re-exposure. In contrast, for fish exposed during the critical windows of embryonic development when epigenetic reprogramming are hypothesised to occur, differential copper accumulation was maintained throughout life. Importantly, the initial exposure caused increased tolerance in the offspring, which was inherited up to the F2 generation. This work provides valuable information regarding potential critical windows of development which may be more susceptible to effects associated with pre-exposure, highlighting that early life exposure to a low concentration of copper can induce differential responses to copper across generations. These data highlight the extent of differential responses to chemical stressors likely to be present in wild populations, and point towards the possibility that effective population management will likely require an in-depth understanding of the exposure history of a given population in order to manage restocking initiatives, and to inform conclusions drawn from toxicity testing studies conducted using individuals originating from wild populations. In addition, these data suggest that it is likely that both epigenetic and genetic changes can contribute to the adaptation of individual populations to their local environment. Finally, other vertebrates including humans have been shown to be exposed to the chemicals tested in this thesis. Therefore, this highlights the potential for these chemicals to also cause toxic effects in humans, potentially via (epi) genetic mechanisms, and advocate the testing of the potential for inheritable phenotypes, such as those described in this thesis, to occur in mammalian models.

Sex and meiosis are ubiquitous in eukaryotes as the primary mode of reproduction. This suggests that despite the theoretical energetic advantages of asexual reproduction, organisms capable of sexual reproduction are at a much greater long-term evolutionary advantage. Rotifers, a group of microinvertebrates, offer unique opportunities to examine the evolution of sex due to their extensive proliferation, successful adaptation to a wide variety of ecological niches, and the diversity of reproductive modes represented in the group. The cyclically parthenogenetic monogonont rotifers have overcome constraints on the loss of sexual reproduction in order to frequently transition between sexual and asexual generations, making them a powerful system with which to address the maintenance of sex in animals. Obligately asexual bdelloid rotifers appear to have thrived without sex for tens of millions of years, a period of time much longer than expected given the hypothesized advantages of sexual reproduction. However, the molecular nature of sex and parthenogenesis is poorly understood in any rotifer species. To expand our knowledge of the molecular mechanisms of monogonont reproduction, we sequenced genomes of two distantly related species, Brachionus calyciflorus and Brachionus manjavacas and identified over 80 homologs for genes involved in meiotic processes. Several of these genes have undergone duplication events specific to the monogonont lineage, including genes with known roles in regulation of cell cycle transitions during meiosis. In addition, global gene expression patterns were determined using obligate parthenogenetic (OP) and cyclical parthenogenetic (CP) strains of B. calyciflorus. Quantitative comparison of expression between these strains revealed differentially expressed genes specific to sexual and asexual reproduction in this species, including genes related to dormancy/resting egg formation, meiosis, and hormone signaling pathways that are thought to be involved in the induction of sexual reproduction in monogononts. Finally, we analyzed gene expression in bdelloid rotifers for evidence of sexual reproduction or the utilization of meiotic genes under conditions inducing high levels of recombination. Through this work, we have established molecular markers for sexuality and asexuality in monogonont rotifers, and used these markers to evaluate reproduction in bdelloids. The data generated specifically allows for more informed analyses of the evolution of cyclical parthenogenesis and rotifer reproduction. Furthermore, this work extends the use of monogononts as a model system for addressing broader questions regarding the evolution of sexual reproduction.

Cancer progression is driven by cumulative changes that promote and maintain the malignant phenotype. Epigenetic alterations are central to malignant transformation and to the development of therapy resistance. Changes in DNA methylation, histone acetylation and methylation, noncoding RNA expression and higher-order chromatin structures are epigenetic features of cancer, which are independent of changes in the DNA sequence. Despite the knowledge that these epigenetic alterations disrupt essential pathways that protect cells from uncontrolled growth, how these modifications collectively coordinate cancer gene expression programs remains poorly understood. In this dissertation, I utilize molecular and informatic approaches to define and characterize the genome-wide epigenetic patterns of two important human cancer cell models. I further explore the dynamic alterations of chromatin structure and its interplay with gene regulation in response to therapeutic agents. In the first part of this dissertation, pancreatic ductal adenocarcinoma (PDAC) cell models were used to characterize genome-wide patterns of chromatin structure. The effects of histone acetyltransferase (HAT) inhibitors on chromatin structure patterns were investigated to understand how these potential therapeutics influence the epigenome and gene regulation. Accordingly, HAT inhibitors globally target histone modifications and also impacted specific gene pathways and regulatory domains such as super-enhancers. Overall, the results from this study uncover potential roles for specific epigenomic domains in PDAC cells and demonstrate epigenomic plasticity to HAT inhibitors. In the second part of this dissertation, I investigate the dynamic changes of chromatin structure in response to estrogen signaling over a time-course using Estrogen Receptor (ER) positive breast cancer cell models. Accordingly, I generated genome-wide chromatin contact maps, ER, CTCF and regulatory histone modification profiles and compared and integrated these profiles to determine the temporal patterns of regulatory chromatin compartments. The results reveal that the majority of alterations occur in regions that correspond to active chromatin states, and that dynamic chromatin is linked to genes associated with specific cancer growth and metabolic signaling pathways. To distinguish ER-regulated processes in tamoxifen-sensitive and in tamoxifen-resistant (TAMR) cell models, we determined the corresponding chromatin and gene expression profiles using ER-positive TAMR cancer cell derivatives. Comparison of the patterns revealed characteristic features of estrogen responsiveness and show a global reprogramming of chromatin structure in breast cancer cells with acquired tamoxifen resistance. Taken together, this dissertation reveals novel insight into dynamic epigenomic alterations that occur with extrinsic stimuli and provides insight into mechanisms underlying the therapeutic responses in cancer cells.

It is well documented that transcriptionally coordinated genes tend to be functionally related, and that such relationships may be conserved across different species, and even kingdoms. (Ihmels et al., 2004). Such relationships was initially utilized to reveal functional gene modules in yeast and mammals (Ihmels et al., 2004), and to explore orthologous gene functions between different species and kingdoms (Stuart et al., 2003; Bergmann et al., 2004). Model organisms, such as Arabidopsis, are readily used in basic research due to resource availability and relative speed of data acquisition. A major goal is to transfer the acquired knowledge from these model organisms to species that are of greater importance to our society. However, due to large gene families in plants, the identification of functional equivalents of well characterized Arabidopsis genes in other plants is a non-trivial task, which often returns erroneous or inconclusive results. In this thesis, concepts of utilizing co-expression networks to help infer (i) gene function, (ii) organization of biological processes and (iii) knowledge transfer between species are introduced. An often overlooked fact by bioinformaticians is that a bioinformatic method is as useful as its accessibility. Therefore, majority of the work presented in this thesis was directed on developing freely available, user-friendly web-tools accessible for any biologist. / Es ist bereits ausgiebig gezeigt worden, dass Gene, deren Expression auf Transkriptionsebene koordiniert ist, häufig auch funktional in verwandten Stoffwechselwegen vorkommen, und dass sich dies wahrscheinlich auch Spezies- und sogar Reichübergreifend sagen lässt (Ihmels et al., 2004). Anfänglich wurden solche Beziehungen verwendet, um sogenannte Genfunktionsmodule in Hefe und Säugern aufzudecken (Ihmels et al., 2004), um dann orthologe Genfunktionen zwischen verschiedene Spezies und Reichen zu entdecken (Stuart et al., 2003; Bergmann et al., 2004). Modellorganismen wie Arabidopsis werden bevorzugt in der Forschung verwendet, weil man durch die schnelle Generationszeit in kurzer Zeit viele Daten erheben kann und aufgrund dessen die Ressourcen- und Informationsvielfalt um ein Vielfaches größer ist. Ein Hauptziel ist der Wissenstransfer von Modellorganismen auf Spezies, die gesellschaftlich von höherer Bedeutung sind wie z.B. Getreidearten oder andere Feldfrüchte. Pflanzen besitzen oft große Genfamilien und die eindeutige Identifizierung von gut charakterisierten Arabidopsisorthologen in besagten Nutzpflanzen ist kein triviales Vorhaben. In der vorliegenden Arbeit werden Konzepte zur Nutzung von Co-expressionsnetzwerken beschrieben, die helfen sollen (i) Genfunktionen zu identifizieren, (ii) die Organisation von biologischen Prozessen aufzuklären und (iii) das erworbene Wissen auf andere Spezies übertragbar zu machen. Ein häufig von Bioinformatikern übersehender Umstand ist, dass bioinformatische Methoden nur so sinnvoll sind wie ihre Zugänglichkeit. Deshalb basiert der Großteil dieser Arbeit auf freiverfügbaren und vor allem für Biologen nutzerfreundlichen Webtools.

Mikromatriser handlar numera inte bara om att alstra genuttrycksdata i snabb takt, utan det är minst lika viktigt att effektivt ta hand om informationen efteråt. I den här avhandlingen presenteras ett arbetsflöde för att mäta, lagra och analysera genuttrycksdata i asp och poppel (Populus spp.). En Populus} mikromatrisdatabas - UPSC--BASE - tillgänglig för alla intresserade, utvecklades i syfte att samla in och lagra genuttrycksdata. Flertalet analysverktyg gjordes samtidigt tillgängliga, för att möjliggöra ett smidigt arbetsflöde från rådata till biologiska slutsatser. En av de stora utmaningarna i analys av mikromatriser är att kunna särskilja bruset från värdefull biologisk information. Att studera träd som växer utomhus är komplext eftersom de interagerar med omgivningen i mycket större utsträckning än vad som är fallet i växthusets kontrollerade miljö. Det här arbetet visar att det är möjligt, med hjälp av avancerad statistik och god försöksplanering, att följa och jämföra genuttrycket i blad från aspar utomhus under flera år för att dra värdefulla slutsatser om geners reglering. Den lagrade biologiska informationen i UPSC-BASE är avsedd att vara en värdefull tillgång för växtfältet i stort. I databasen finns nästan hundra olika experiment som innefattar alltifrån unga blad till ved, insektsangrepp, kyla och torka samt studier av genmodifierade växter. Informationen kan användas både för jämförande studier inom olika aspförsök, men också för att jämföra med andra växter. För att illustrera möjligheterna, studerades och grupperades gener i blad baserat på hur de uppträder över alla dessa experiment. Dessa grupperingar användes sedan för att definiera gener som är viktiga i bladutvecklingen. Sammanfattningsvis ger arbetet som presenteras i denna avhandling tillgång till verktyg och kunskap för storskaliga studier av genuttryck och den lagrade informationen har bevisats vara en värdefull tillgång för mer ingående studier av geners reglering. / DNA microarray analysis today is not just generation of high-throughput data, much more attention is paid to the subsequent efficient handling of the generated information. In this thesis, a pipeline to generate, store and analyse Populus transcriptional data is presented A public Populus microarray database - UPSC--BASE - was developed to gather and store transcriptomic data. In addition, several tools were provided to facilitate microarray analysis without requirements for expert-level knowledge. The aim has been to streamline the workflow from raw data through to biological interpretation. Differentiating noise from valuable biological information is one of the challenges in DNA microarray analysis. Studying gene regulation in free-growing aspen trees represents a complex analysis scenario as the trees are exposed to, and interacting with, the environment to a much higher extent than under highly controlled conditions in the greenhouse. This work shows that, by using multivariate statistics and experimental planning, it is possible to follow and compare gene expression in leaves from multiple growing seasons, and draw valuable conclusions about gene expression from field-grown samples. The biological information in UPSC-BASE is intended to be a valuable transcriptomic resource also for the wider plant community. The database provides information from almost a hundred different experiments, spanning different developmental stages, tissue types, abiotic and biotic stresses and mutants. The information can potentially be used for both cross-experiment analysis and for comparisons against other plants, such as Arabidopsis or rice. As a demonstration of this, microarray experiments performed on Populus leaves were merged and genes preferentially expressed in leaves were organised in to regulons of co-regulated genes. Those regulons were used to define genes of importance in leaf development in Populus. Taken together, the work presented in this thesis provides tools and knowledge for large-scale transcriptional studies and the stored gene expression information has been proven to be a valuable information resource for in-depth studies about gene regulation.