Cytokinesis involves constriction of the cell at the equator. Without decreasing in volume, a spherical cell requires a net increase in the surface area during this constriction. The constriction is driven by formation of an actomyosin contractile ring, and the surface increase by addition of membrane during the formation of the cleavage furrow. Both events depend on the central spindle microtubules at the midzone of the spindle and, in particular, on the centralspindlin protein complex. The communication between the central spindle microtubules and the actomyosin ring involves binding of a GAP and a GEF for RhoA to the centralspindlin kinesin Pavarotti/MKLP1. However, it is still unclear which molecular machinery connects the mitotic spindle to membrane trafficking during cleavage furrow ingression. ARF6 is a member of the ARF family of small GTPases, and previous studies suggest that it is an important regulator of membrane trafficking through the endocytic pathway, and cortical Actin remodelling. I generated an arf6 null mutant in Drosophila. arf6 null mutants survive to adulthood without obvious morphological defects, indicating that ARF6 is not required for Drosophila somatic development. However, ARF6 is required for cytokinesis in Drosophila spermatocytes. The centralspindlin kinesin Pavarotti, identified as an ARF6 interactor in a Yeast-2-Hybrid assay, binds ARF6 in GST pulldowns, and interacts genetically with the arf6 mutant. ARF6 localizes to the plasma membrane and a population of early and recycling endosomes. During cytokinesis, ARF6 is enriched on recycling endosomes at the central spindle. arf6 mutants form a cleavage furrow during cytokinesis, which later regresses. Cytokinesis in arf6 mutant spermatocytes lacks the rapid plasma membrane expansion observed during normal divisions. The results of this study suggest that ARF6 might promote rapid recycling of endosomal membrane stores at the central spindle to the plasma membrane during cytokinesis. ARF6 might be recruited to the central spindle via its interaction with Pavarotti, and act as part of the molecular link between the central spindle cytoskeleton and the rapid plasma membrane addition necessary for cytokinesis. Für die Ansicht der quick-time-Movies mit der Endung "avi" ist die Installation des "Apple QuickTime-Players" erforderlich.

Sterol is an abundant component of eukaryotic cell membranes and is thought to influence membrane properties such as permeability, fluidity and microdomain formation. Drosophila is an excellent model system in which to study functional requirements for membrane sterol because, although it does not synthesize sterol, it nevertheless requires sterols to complete development. Moreover, Drosophila normally incorporates sterols into cell membranes. Thus, dietary sterol depletion can be used to specifically reduce membrane sterol levels. In contrast, vertebrates do synthesize cholesterol. In this way, sterol depletion in vertebrates demand the use of approaches such as chemical extractions, drug treatments or genetic manipulation which are prone to have side effects. We have controlled the level and type of dietary sterol available to developing Drosophila larvae in order to investigate the requirement for sterol in cell membranes, and to distinguish it from the function of sterol as a precursor for signaling molecules. Strikingly, we show that membrane sterol levels can be reduced 6-fold in most tissues without affecting cell or larval viability. Larvae respond to sterol depletion by arresting their growth and development, and by increasing the level of specific sphingolipid variants that promote survival when sterol is scarce. Thus, non-sterol lipids are able to substitute for sterols in the maintenance of basic membrane biophysical properties required for life. Despite this, Drosophila larvae regulate their growth to maintain membrane sterol levels within tight limits. The existence of this novel membrane sterol-dependent growth control mechanism indicates an important role for bulk membrane sterol in the tissue specific functions of differentiated cells.

Gene regulation lies at the heart of most biological processes and transcription factors are the key molecules that control tissues specific gene expression. In higher eukaryotes transcription factors control gene expression by binding regulatory DNA segments called cis-regulatory modules (CRMs). The increasing number of sequenced genomes of multicellular eukaryotes along with high-throughput methods such as whole genome microarray expression data allows for systematic characterization of the CRMs that control gene expression. A first step towards understanding gene regulation is the identification of the regulatory elements present in the genome. We take advantage of the large database of spatio-temporal patterns of gene expression in D. melanogaster embryogenesis to identify sets of developmentally co-expressed genes. We developed a computational method that identifies DNA binding sites for transcription factors from families of co-regulated genes that are expressed during Drosophila embryo development. This method discovers over-represented motifs in a set of co-regulated genes using the exhaustive motif enumeration technique. Clustering the predicted motifs identifies the CRMs, which assist in translating a combinatorial code of TF inputs into a specific gene expression output. The predicted CRMs were verified experimentally by searching the whole genome for the predicted CRMs and establishing expression pattern of the genes that are associated with these CRMs. It is well know that the gene expression is substantially controlled through CRMs and those key regulatory sequences are conserved in related species. The conservation of CRMs can be studied by comparing the related genomes and alignment methods are widely used computational tools for comparing the sequences. However, in distantly related species the CRM sequences are simply not align able. To identify the similar CRMs in distantly related species we developed a non-alignment based method for discovering similar CRMs in related species. This method is based on word frequencies where the given sequences are compared using Poisson based metric. When starting with a set of CRMs involved in Drosophila early embryo development, we show here that our non-alignment method successfully detects similar CRMs in distantly related species ( D. ananassae, D. pseudoobscura, D. willisoni, D. mojavensis, D. virilis, D. grimshawi ). This method proved efficient in discriminating the functional CRMs from the non-functional ones.

Als Quorum sensing (QS) wird die Kommunikation zwischen Bakterien bezeichnet. Diese basiert auf kleinen Signalmolekülen, die Autoinducer (AI) genannt werden. Durch QS werden von Bakterien Verhaltensweisen wie Fähigkeit zur Symbiose, Virulenz, Produktion von Antibiotika und Bildung von Biofilmen reguliert. Die Kommunikation kann innerhalb einer Spezies (Intraspezies-Kommunikation) oder mehreren Spezies (Interspezies-Kommunikation) erfolgen. Gram-negative Bakterien kommunizieren über acetylierte Homoserinlaktone (AHL), Gram-positive Bakterien dagegen benutzen modifizierte Oligopeptide als Autoinducer. Für die Interspezies-Kommunikation dient der Autoinducer-2 (AI-2). AI-2 entsteht auf dem Weg der spontanen Zyklisierung von 4,5-Dihydroxy-2,3-Pentadion (DPD), der von LuxS synthetisiert wird. Die Universalität des AI-2 als Signalmoleküls basiert auf dessen chemischen Eigenschaften. Als biologisch aktive Formen von DPD gelten S-THMF-Borat (bei marinen Bakterien wie Vibrio harveyi) und R-THMF (z.B. bei Enterobakterien wie Escherichia coli oder Salmonella enterica Serovar Typhimurium). AI-2 wird bei allen Bakterien von einem periplasmatischen Rezeptor gebunden. S-THMF-Borat bindet spezifisch an den Rezeptor LuxP, R-THMF dagegen an den Rezeptor LsrR. Durch die Anbindung des AI-2 verändert sich die Konformation des Rezeptors, was als Signal über weitere Proteine in die Zelle weitergeleitet wird. In E. coli ist die Expression des Operons lsrACDBFGE von AI-2 abhängig. Der lsr-Promotor wird von dem Repressor LuxR, Phospo-AI-2 sowie dem cAMP-CRP-Komplex reguliert. In dieser Arbeit wurden die molekularbiologische Grundlagen zur Entwicklung eines AI-2-Biosensors gelegt. Es wurden mehrere Fusionskonstrukte des V. harveyi AI-2 Rezeptors LuxP sowie dessen Derivate mit veränderter Affinität zur AI-2 kreiert, in E. coli exprimiert und aufgereinigt. Auch Rezeptorproteine von Vibrio fischeri sowie E. coli konnten erfolgreich exprimiert werden. Die Expression der Proteine erfolgte in E. coli luxS- Deletionsstämmen, die hierfür konstruiert worden sind. Die AI-2-Rezeptorproteine werden in E. coli vorwiegend in Form von inclusion bodys exprimiert. Nur ein Teil des Proteins ist löslich und kann für die Aufreinigung unter nativen Bedingungen verwendet werden. Auf der Basis von E. coli luxS- Deletionsstämmen wurde ein Bioassay entwickelt, der für die Detektion von AI-2 verwendet werden kann. Hierfür wurden mehrere Reporterplasmide konstruiert, in denen das rot fluoreszierende Protein DsRed unter die Kontrolle des lsr-Promotors von E. coli kloniert wurden. Dabei konnte unter Verwendung einer dieser Reporterplasmide (pBRDsRed) sowie des luxS-Deletionsstammes KIB1 Bioassay-Bedingungen etabliert werden, die einen Nachweis von AI-2 ermöglichen. Die für den Assay benötigten AI-2-Moleküle wurden in vitro mithilfe der Enzyme Pfs und LuxS und S-Adenosyl-Homocystein (SAH) als Substrat hergestellt. Der entwickelte AI-2-Bioassay wurde für die Bestimmung der Bindeaktivität der V. harveyi LuxP-Derivate verwendet. Die resultierenden Ergebnisse wiesen eine hohe Reproduzierbarkeit (1,2 bis 11,3 % Standartabweichung) auf.

The development of multicellular organisms is dependent on the tight coordination between tissue growth and morphogenesis. The stereotypical orientation of cell divisions has been proposed to be a fundamental mechanism by which proliferating and growing tissues take shape. However, the actual contribution of stereotypical cell division orientation (SDO) to tissue morphogenesis is unclear. In zebrafish, cell divisions with stereotypical orientation have been implicated in both body axis elongation and neural rod formation, although there is little direct evidence for a critical function of SDO in either of these processes. Making use of extended time-lapse, multi-photon microscopy and a careful three-dimensional analysis of cell division orientation, we show that SDO is required for neural rod midline formation during neurulation, but dispensable for body axis elongation during gastrulation. Our data indicate that SDO during both gastrulation and neurulation is dependent on the non-canonical Wnt receptor Frizzled 7 (Fz7), and that interfering with cell division orientation leads to severe defects in neural rod midline formation, but not body axis elongation. These findings suggest a novel function for Fz7 controlled cell division orientation in neural rod midline formation during neurulation. They also shed new light on the field of cell division orientation by uncoupling it from tissue elongation.

Die Bildung neuen Nervenzellen im erwachsenen Gehirn—adulte Neurogenese—ist bei Säugetieren auf spezifische Regionen beschränkt. Eine der beiden bekannten ist der Hippokampus, eine Gehirnstruktur, die eine wichtige Rolle beim Lernen sowie der Gedächtnisbildung spielt. Ein Reservoir von neuralen Stammzellen befindet sich in der subgranulären Zone des hippokampalen Gyrus dentatus. Diese Zellen teilen sich fortwährend und bilden neue Nervenzellen. Die Regulation adulter hippokampaler Neurogenese wird sowohl von der Umgebung beeinflusst als auch von mehreren Genen gesteuert. In der vorliegenden Arbeit wurden mittels Hochdurchsatz- Genexpressionsverfahren die an der Neurogenese beteiligten Gene identifiziert und ihr Zusammenspiel untersucht. Anhand von genetischen, umgebungsbedingten und zeitlichen Angaben und Variationen wurde ein vielseitiger Datensatz erstellt, der einen multidimensionalen Blick auf den proliferativen Phänotyp verschafft. Netzwerke aus Gen-Gen und Gen-Phänotyp Interaktionen wurden beschrieben und in einer mehrschichtigen Ressource zusammengefasst. Ein Kern-Netzwerk bestehend aus immerwiederkehrenden Modulen aus verschiedenen Ebenen wurde anhand von Proliferation als Keim-Phänotyp identifiziert. Aus diesem Kern-Netzwerk sind neue Gene und ihre Interaktionen hervorgegangen, die potentiell bei der Regulierung adulter Neurogenesis beteiligt sind. / Neurogenesis, the production of new neurons, is restricted in the adult brain of mammals to only a few regions. One of these sites of adult neurogenesis is the hippocampus, a structure essential for many types of learning. A pool of stem cells is maintained in the subgranular zone of the hippocampal dentate gyrus which proliferate and can differentiate into new neurons, astrocytes and oligodendroctytes. Regulation of adult hippocampal neurogenesis occurs in response to en- vironmental stimuli and is under the control of many genes. This work employs high-throughput gene expression technologies to identify these genes and their interactions with each other and the neurogenesis phenotype. Harnessing variation from genetic, environmental and temporal sources, a multi-faceted dataset has been generated which offers a multidimensional view of the neural precursor proliferation phenotype. Networks of gene-gene and gene-phenotype interac- tions have been described and merged into a multilayer resource. A core subnetwork derived from modules recurring in the different layers has been identified using the proliferation phenotype as a seed. This subnetwork has suggested novel genes and interactions potentially involved in the regulation of adult hippocampal neurogenesis.

Zur Einschätzung der Goldführung von 26 ausgewählten Sand- und Kieslagerstätten in Sachsen wurden Proben auf ihre Goldgehalte untersucht. Die Mehrzahl der untersuchten Großproben wies Goldgehalte unterhalb der durchschnittlichen Zusammensetzung der Erdkruste auf. Eine mögliche Gewinnbarkeit des Goldes in Kies- und Sandlagerstätten hängt vom Goldgehalt im Rohkies und von der Anreicherung im Laufe der Aufbereitung im Tagebaubetrieb ab. Entscheidenden Einfluss auf die Gewinnung haben auch Korngröße und Kornform der Goldflitter. Die Broschüre fasst die Ergebnisse der Untersuchung zusammen und gibt Empfehlungen für das weitere Vorgehen.

Microtubules are tubular polymers that are involved in a variety of cellular processes such as cell movement, mitosis and intracellular transport. The dynamic behavior of microtubules makes this possible because all of these processes require quick responses. Embryonic stem (ES) cells were first isolated from mouse embryos and they have two unique characteristics; they can be kept undifferentiated for many passages with a stable karyotype and they can be differentiated into any type of cells under appropriate conditions. The pluripotency of ES cells, their ease of manipulation in culture, and their ability to contribute to the mouse germ-line provides us a model of differentiation both in vitro and in vivo. In my thesis I focused on the cell division and neuronal differentiation of ES cells and developed two methods to understand the effects of microtubule dynamics in spindle assembly and chromosome segregation and to reveal the roles of different Microtubule Associated Proteins (MAPs) in the neuronal morphology formation. In the first part, we developed a live-cell imaging method for ES cells to visualize, track and analyze the single cell behavior in a cell population over a time period. So far many techniques have been adapted and combined for imaging of cell lines, mainly for the cancer or immortalized ones. However, because ES cells are very prone to apoptosis, tend to form spheres and hard to stably label, it is quite tricky to image them in culture conditions. In our system, we combined the BAC-based gene expression with wide-field deconvolution microscopy for ES cells that are plated onto the laminin-511 coated surface and kept in CO2 independent culture conditions. This combined technique does not interfere with the growth of cells and keeps them healthy up to 24 hours on the microscope stage. In the second part, we analyzed the effects of MAPs chTOG, EB1, Kif18A and MCAK in the overall spindle morphology and mitotic progression in mES cells. For this purpose, we utilized our stable TUBB-GFP and H2A-GFP cell lines along with our live-cell imaging set-up to reveal the effects of the above-mentioned proteins and the interplay among each other. By using RNAi method we either single or co-depleted the genes by siRNAs and measured the spindle length and width in RNAi conditions. We further analyzed the mitotic progression in H2A-GFP cell line in terms of the metaphase timing and the percentage of chromosome segregation errors. Our results showed that, EB1 depletion did not cause any significant changes in the overall spindle morphology or in the metaphase timing. However, the co-depletion of EB1 with chTOG partially rescued the sichTOG specific mini-spindle phenotype. siKif18A produced longer spindles without any change in the spindle width. Surprisingly, the co-depletion of antagonistic chTOG and Kif18A proteins had additive effects on the spindle dynamics and on mitotic progression in a way that spindle assembly was severely disrupted by the absence of these two proteins and as a result of this, both metaphase timing and chromosome missegregation levels increased significantly. These results overall indicate that MAPs have important roles in the regulation of dynamic instability and these proteins have an interplay among each other to be able to control the morphology of the spindle as well as the correct segregation of chromosomes into daughter cells. In the last part, I will introduce you a new ES cell based differentiation and morphology model, which brings the advantages of high resolution imaging capacity, control over development and easy genetic manipulation and culturing. We have generated Tet-induced shRNA cell lines against chTOG, Kif18A and MCAK, which are also stably expressing TUBB-GFP. These labeled cells were mixed with unlabeled wild-type mES cells before differentiation at 1:1000 ratio and then they were differentiated into mouse cortical cells and spinal motor neurons. Our results showed that, all of the three genes could be successfully knocked-down by shRNA after 48 hours of Tet induction. After mixing the labeled and unlabeled cells, single neurons could be imaged at high resolution and their skeletons could be generated afterwards. The RNAi studies in shchTOG cell line showed that, the knock-down of this gene in early differentiation interferes with the neuronal differentiation.

Methylation of histone 3 (H3) at lysine 36 (K36) has been implicated in several biological processes, such as DNA replication, DNA repair, and transcription. To date, at least eight distinct mammalian enzymes have been described to methylate H3K36 in vitro and/or in vivo. In this work, Set2, Nsd1, and Nsd3 Venus tagged proteins were successfully expressed in mouse embryonic stem cells and, then, analyzed by confocal microscopy, mass spectrometry (MS), and chromatin immunoprecipitation sequencing (ChIP-seq). MS analysis revealed that Setd2, Nsd1, and Nsd3 do not associate in protein complexes with each other. Setd2 was associated with RNA polymerase II subunits and two transcription elongation factors (Supt5 and Supt6), whereas Nsd1 associated with the transcription factor Zfx. In contrast, Nsd3 interacted with multiple protein complexes including Kdm1b and Brd4 complexes. Interestingly, Nsd1 and Zfx seem to be bound to chromatin during cell division. ChIP-seq analysis of the H3K36 methyltransferases showed different binding profiles at transcribed genes: Nsd1 binds near the transcription start site (TSS), Setd2 loading starts near the TSS and spreads along the gene body, while, Nsd3 is preferentially enriched at the 5’ and 3’ gene regions. Sequential deletion of PWWP and zinger-finger like domains was achieved to study any possible changes in Nsd1 and Nsd3 function. Deletion of either PHD1-4 or PHD5/C5HCH domains decreased Nsd1 recruitment to chromatin. Particularly, the PHD5/C5HCH were identified as the protein-protein interface for Zfx interaction. In agreement, Zfx knockdown also decreased Nsd1 deposition at the Oct4 and Tcl1 promoter regions. Furthermore, Nsd1 depletion reduced bulk histone H3K36me2 and histone H3K36me3 loading at the coding regions of Oct4, Rif1, Brd2, and Ccnd1. In addition, Nsd1 knockdown led to an increased Zfx deposition at promoters. Our findings suggest Zfx recruits Nsd1 to its target loci, whereas Nsd1 regulates Zfx chromatin release and further contributes to transcription regulation through its H3K36 dimethylase activity. On the other hand, loss of Nsd3’s PHD5/C5HCH or PWWP domains decreased Nsd3 binding to DNA. In addition, we demonstrate that Nsd3 is recruited to target genes in a Brd4-dependent manner. Herein, we provided further insights on how H3K36 methyltransferases are regulated, and how they contribute to changes in the epigenetic landscape in mouse embryonic stem cells.fi

The regenerative potential of adult stem cell populations within the human body bears great promises for their use in regenerative medicine. The bone marrow (BM) harbours two different types of adult stem cells, haematopoietic stem and progneitor cells (HSPCs) and multipotent mesenchymal stromal cells (MSCs), which are tightly regulated in their distinct anatomically defined niches by multiple cues such as cytokines, cell-cell contacts, the extracellular matrix (ECM) and the physical microenvironment. The ex vivo expansion of these cells for applications in regenerative therapies is of great interest and several biomaterial approaches attempt to mimic the natural BM niche and its components to control stem cell maintenance and differentiation. However, as of now the complexity of such stem cell niches is hard to recapitulate. Towards this goal, this work was focussing on the ECM environment of BM stem cells and was set out to engineer improved in vitro culture systems. MSC themselves are one of the most important cell types within the BM that secrete and construct ECM-networks and thereby shape the microenvironment of the residing cells. The potential of primary human BM-MSC to secrete ECM in vitro has been exploited to generate niche-like ECM surrogates in a robust and versatile format. Application of decellularisation regimes allowed the fabrication of complex matrices which demonstrated suprastructural, compositional and physicochemical properties compareable to those of the native BM-ECM environment. Reliable stability and reproduciblity was achieved by a dedicated procedure of maleic anhydride co-polymer-mediated covalent binding of fibronectin and subsequent anchorage of cell-secreted ECM molecules. As a result of the high reproducibility, a complete proteomic register of ECM molecules was obtained in combination with determining the complex fibrillar and soft gel-like characteristics of MSC-derived matrices. Based on the established BM niche-like substrate, the impact of extracellular matrices on MSC and HSPC ex vivo behavior has been explored. Both cell types demonstrated strong adhesion to ECM substrates and depicted a changed cellular morphology upon contact with native ECM structures compared to standard culture substrates or simple ECM protein coatings, indicating an intense interplay between the cell and the microenvironment. MSC that re-grew into their own matrices have shown advantageous proliferation and cytokine secretion levels as well as enhanced differentiation intensity (upon differentiation induction) compared to MSC that were cultured on less complex substrates. Similarly, HSPC were also instructed for enhanced expansion on MSC-derived matrices without exhaustion of stem cell-marker expressing progenitor cells. The efficiency of these matrices was related to their ability to mimic the native composite suprastructure, ligand nano-topography, molecular composition and physical properties of natural BM ECM environments. The data obtained within this thesis set the ground for a more rational design of artificial stem cell niches with defined and distinct properties, offering exciting options for the in-depth analysis and understanding of stem cell regulation by exogenous cues.