Wnt proteins have key roles in patterning of multicellular animals, acting at a distance from their sites of production. However, it is not well understood how these molecules propagate. This question has become even more puzzling by the discovery that Wnts harbour post-translational lipid-modifications, which enhance association with membranes and may therefore limit propagation by simple diffusion in an aqueous environment. The cellular mechanisms involved in Wnt propagation are largely unknown for vertebrate organisms. Here, I discuss my findings on the cellular localization of zebrafish Wnt8, as an example of a vertebrate Wnt. Wnt8 is a key signal for positioning the midbrain-hindbrain brain boundary (MHB) organizer along the anterior-posterior axis of the developing brain in vertebrates. However, it is not clear how this protein propagates from its source, the blastoderm margin, to the target cells, in the prospective neural plate. For this purpose, I have analysed a biologically active, fluorescently tagged Wnt8 in live zebrafish embryos. Wnt8 was present in live tissue in membrane associated punctate structures. In Wnt8 expressing cells these puncta localise to filopodial cellular processes, from which the protein is released to neighbouring cells. This filopodial release requires posttranslational palmitoylation. Although palmitoylation-defective Wnt8 retains auto- and juxtacrine signaling activity, it fails to signal over a long-range. Additionally, this Wnt8 palmitoylation is necessary for regulation of its neural plate target genes. These results suggest that vertebrate Wnt proteins use cell-to-cell contact through filopodia as a shortrange propagation mechanism while released palmitoylated Wnt is required for longrange signaling activity. Furthermore, I show that a Wnt8 receptor, Frizzled9 can negatively influence Wnt8 propagation and signaling range. Finally, I was able to determine the presence of an endogenous Wnt8 gradient in the neurectoderm. I discuss these findings in the context of Wnt8 signaling function in mediating anterior-posterior patterning during early brain development.

Angiogenese ist entscheidend für die meisten physiologische Prozesse und viele pathologische Umstände. Dabei wird Angiogenese durch die Interaktion zwischen der extrazellulären Matrix (ECM) und endothelialen Zellen reguliert. Während der kardiovaskulären Entwicklung im Zebrafisch fördert Klf2, ein blutstrom-sensitiver Transkriptionsfaktor, die VEGF-abhängige Angiogenese. Der Mechanismus, bei dem biophysikalische Reize die Klf2 Expression regulieren und Angiogenese kontrollieren, ist größtenteils unbekannt. In meiner Studie zeige ich, dass erhöhte klf2 mRNA Expression den molekularen und morphogenetischen kardiovaskulären Defekten in Zebrafisch ccm Mutanten zugrundeliegen. Desweiteren zeige ich, dass diese Defekte durch verstärkte egfl7-Expression und Angiogenese vermittelt werden. Meine Studie zeigt ausserdem, dass die Klf2-Expression unabhängig vom Blutstrom durch den Extrazellularmatrix-bindenden Rezeptor beta1 Integrin reguliert wird. Der CCM-Protein-Komplex, zusammen mit dem ihm verbundenden Integrin-regulierenden Protein ICAP-1 verhindert ein verstärktes Angiogenese-Signal in endothelialen Zellen, indem es die beta1 Integrin-abhängige Klf2 Expression begrenzt. Zusammenfassend zeigt meine Arbeit einen neuen beta1 Integrin-Klf2-Egfl7 Signalweg, der durch zerebrale kavernöse malformations (CCM) Proteine reguliert wird / Angiogenesis is critical to most physiological processes and many pathological conditions. This process is controlled by physical interactions between the extracellular matrix (ECM) and endothelial cells. Klf2, a blood flow–sensitive transcription factor, promotes VEGF-dependent angiogenesis during zebrafish cardiovascular development. However, the mechanism by which biophysical stimuli regulate Klf2 expression and control angiogenesis remains largely unknown. In my study, I show that elevated klf2 mRNA levels underlie the molecular and morphogenetic cardiovascular defects in zebrafish ccm mutants. Furthermore, I demonstrate that these defects are mediated by enhanced egfl7 expression and angiogenesis signaling. My study also revealed that Klf2 expression is regulated by the extracellular matrix-binding receptor beta1 integrin in the absence of blood flow. The CCM protein complex and its associated beta1 integrin-regulatory protein ICAP-1 prevents increased angiogenesis signaling in endothelial cells by limiting beta1 integrin-mediated expression of Klf2. ln sum, my work uncovered a novel beta1 integrin-Klf2-Egfl7 signaling pathway, which is regulated by the cerebral cavernous malformations (CCM) proteins.

Oscillations are present at many different levels of biological organization. The cell cycle that directs the division of individual cells, the regular depolarization of neurons in the sinu-atrial node which underlies the regular beating of the heart, the circadian rhythms that govern the daily activity cycles of virtually all organisms, and the clocks that make entire populations of fireflies flash on and off in unison feature as prominent examples of biological clocks. During development, biological clocks regulate the patterning of growing tissues, as is the case in vertebrate somitogenesis, and potentially also in vertebrate limb outgrowth and axial segmentation of invertebrate embryos. During vertebrate segmentation, the embryonic axis is subdivided along its anterior-posterior axis into epithelial spheres of cells called somites. This rhythmic process is thought to be driven by a multicellular oscillatory gene network, the so-called segmentation clock. Oscillations of hairy and enhancer of split gene products have been proposed to constitute the core clockwork in individual cells, and these oscillators are coupled to each other by Delta-Notch intercellular signaling. The interaction of the segmentation clock with a posteriorly-moving arrest wavefront then translates the temporal information encoded by the clock into a spatial pattern of segments. In the framework of this Clock and Wavefront model, segment length is determined by both clock period and arrest wavefront velocity. How the period of the segmentation clock is regulated is presently unknown, and understanding the mechanism of period setting might yield insight into the nature and function of the segmentation clock. In this study, two different but complementary approaches were pursued to investigate how period is regulated in the zebrafish segmentation clock. First, it has been reported that zebrafish mind bomb (mib) mutant embryos form somites more slowly than their wt siblings, suggesting that Mib might be implicated in period setting. Mib is an E3 ubiquitin ligase required for ubiquitination and endocytosis of the Notch ligand Delta, and Notch signaling is impaired in mutants with defective Mib. It has been suggested that the mechanistic basis for the requirement of Delta endocytosis in Notch signaling is a need for Delta to enter a particular endocytic compartment, potentially a recycling endosome, in a ubiquitin-dependent manner, where its signaling ability might be established or amplified by an as yet unknown posttranslational modification. In the present study, Delta trafficking through the endocytic pathway was analyzed in the PSM of wt and mib embryos through colocalization studies with endocytic markers. The rationale of this approach was that if Delta gained access to a particular endocytic compartment through Mib-dependent endocytosis, the presence of Delta in this compartment would be expected to be reduced in mutants with defective Mib, thereby revealing the compartment’s identity. However, no qualitative changes in colocalization with different endocytic markers could be detected in mib mutants, and the methods available did not allow for quantification of colocalization in wt or mutant backgrounds. However, Delta colocalized with 13 markers of recycling endosomes, consistent with the hypothesis that these are functionally important in Notch signaling. More refined techniques will be necessary for a quantitative analysis of normal as compared to impaired Delta trafficking. A genetic approach to period regulation proved to be successful for the Drosophila circadian clock, where the identification of period mutants advanced the understanding of the clock’s genetic circuitry. This motivated a screen for period mutants of the segmentation clock, which was carried out by measuring somitogenesis period, segment length and arrest wavefront velocity in a pool of candidate mutants. A subset of Delta-Notch mutants, and embryos treated with a small-molecule inhibitor that impairs Notch signaling, displayed correlated increases in somitogenesis period and segment length, while there was no detectable change in arrest wavefront velocity. Combined, these findings suggested that segmentation clock period is increased in experimental conditions with impaired Delta-Notch signaling. Using a theoretical description of the segmentation clock as an array of coupled phase oscillators, the delay in the coupling and the autonomous frequency of individual cells were estimated from the direction and magnitude of the period changes. The mutants presented here are the first candidates for segmentation clock period mutants in any vertebrate. The nature of the molecular lesions in these mutants, all of which affect genes implicated in intercellular Delta-Notch signaling, suggests that communication between oscillating PSM cells is a key factor responsible for setting the period of the segmentation clock.

Fibroblast growth factor (Fgf) signaling plays multiple inductive roles during development of vertebrates (Itoh 2007). Some Fgfs, such as Fgf8, are locally secreted and signal over a long range to provide positional information in the target tissue (Scholpp and Brand 2004). Fgf ligands signal in a receptor-dependent manner via tyrosine kinase receptors, four of which have been so far identified. Fgf8 signaling was shown to depend both on receptor activation as well as endocytosis. The specificity of Fgf ligands and receptors as well as the function of receptors in the control of the Fgf signaling range have been, however, largely unclear. In this study, we show that the putative Fgf8 receptor Fgfr1 is duplicated in zebrafish and that it acts redundantly in the formation of the posterior mesoderm. Also, in overexpression studies we confirm the notion that receptor endocytosis influences Fgf8 signaling range. Through TILLING mutant recovery and morpholino knockdown studies we also show that Fgfr2 is required for growth and skeletal development in zebrafish, whereas Fgfr4 is required for pectoral fin specification and growth.

Developmental biologists try to elucidate how it is possible for cells, all originating from the same egg, to develop into a variety of highly specialized structures, such as muscles, skin, brain and limbs. What organizes the behavior of these cells, and how can the information encoded in the DNA account for the observed patterns and developmental processes? Cell movements and tissue flow during embryogenesis constitute a beautiful problem of bridging scales: On the microscopic scale, cells are expressing particular genes which determine their identities and also their fate during morphogenesis. These molecular determinants then lead to the macroscopic phenomena of cell movements and tissue arrangements, for which one needs a continuum description in terms of active fluids. Taking into account that the number of cells is fairly small, a complete coarse graining is not possible, and a characterization of both mesoscopic (individual cell motion) and macroscopic (flow) behavior is required for a full description. In the here presented work, a set of different experimental methods was applied to investigate the mechanical and dynamical properties of zebrafish embryonic cells and tissues. This thesis is structured as follows: In chapter 2, we introduce the fundamental concepts that are important for the study of cell motion during zebrafish embryonic development. In chapter 3, the materials and methods applied in this work are described. The experimental results of my thesis-work are presented in chapters 4-8: Chapter 4 concentrates on the physical properties of whole tissues. It is shown that tissues are viscoelastic materials. Tissue viscoelasticity is not a new concept, but this study is the first one to quantify the mechanical properties of tissues that are in actual contact in a developing embryo. In chapter 5, cell rearrangements in culture, such as cell sorting and tissue wetting are discussed. These experiments show that tissue interactions are largely determined by tissue surface and interfacial tensions. In chapter 6, an optical stretcher device is applied to measure, solely by means of laser light, the material properties of individual cells. Hereby it is shown that single cells from the two investigated tissue types differ in their mechano-physical properties. After the study of cell and tissue mechanics, the dynamics of cell migration in three dimensions in tissue aggregates and in developing zebrafish embryos is addressed: In chapter 7, 3D-cell migration in multicellular aggregates is analyzed quantitatively by studying the mean square displacement, cell velocity distribution and velocity autocorrelation. In chapter 8, we study the cell motion within the developing zebrafish embryo. By following the motion of many cells in four dimensions, we are able to generate a velocity flow profile for this cell-flow. Chapter 9 gives a brief summary of the obtained results and an outlook to future projects motivated by the presented study. The final part of this thesis are four appendices. Appendix A contains protocols and additional methods. Appendix B contains several calculations, whose results were used in the main part of this work. Appendix C contains additional data and discussions, which were excluded from the main part due to space limitations. Finally, Appendix D consists of a compact disc with 11 movies and a movie description, which serves as supplemental material to the presented data. (Die Druckexemplare enthalten jeweils eine CD-ROM als Anlagenteil: 650 MB: Movies - Nutzung: Referat Informationsservice der SLUB)

Biological information processing in living systems like cells, tissues and organs critically depends on the physical interactions of molecular signaling components in time and space. How endocytic transport of signaling molecules contributes to the regulation of developmental signaling in the complex in vivo environment of a developing organism is not well understood. In a previously performed genome-wide screen on endocytosis, several genes have been identified, that selectively regulate transport of signaling molecules to different types of endosomes, without disrupting endocytosis. My PhD thesis work provides the first functional in vivo characterization of one of these candidate genes, the novel, highly conserved Rab5 effector protein P95 (PPP1R21). Cell culture studies suggest that P95 is a novel endocytic protein important to maintain the balance of distinct endosomal sub-populations and potentially regulates the sorting of signaling molecules between them (unpublished work, Zerial lab). The scientific evidence presented in this study demonstrates that zebrafish P95 is essential for early zebrafish embryogenesis. Both, knockdown and overexpression of zebrafish P95 compromise accurate morphogenetic movements and patterning of the zebrafish gastrula, showing that P95 functions during zebrafish gastrulation. P95 is functionally required to maintain signaling activity of signaling pathways that control embryonic patterning, in particular for WNT/β-catenin signaling activity. Knockdown of zebrafish P95 amplifies the recruitment of β-catenin to early endosomes, which correlates with the limitation of β-catenin to translocate to the nucleus and function as transcriptional activator. The obtained results suggest that zebrafish P95 modulates the cytoplasmic pools of β-catenin in vivo, via endosomal transport of β-catenin. In conclusion, the data presented in this thesis work provides evidence that the cytoplasm-to-nucleus shuttling of β-catenin is modulated by endocytic trafficking of β-catenin in vivo. We propose the endocytic modulation of β-catenin cytoplasm-to-nucleus trafficking as potential new mechanism to fine-tune the functional output of WNT/β-catenin signaling during vertebrate gastrulation.

Mutations in the leucine-rich repeat kinase 2 (LRRK2) gene are a major cause of Parkinson’s disease (PD), which is why modelling PD by replicating effects in animal models attracts great interest. However, the exact mechanisms of pathogenesis are still unclear. While a gain-of-function hypothesis generally receives consensus, there is evidence supporting an alternative loss-of-function explanation. Yet, neither overexpression of the human wild-type LRRK2 protein or its pathogenic variants, nor Lrrk2 knockout recapitulates key aspects of human PD in rodent models. Furthermore, there is conflicting evidence from morpholino knockdown studies in zebrafish regarding the extent of zygotic developmental abnormalities. Because reliable null mutants may be useful to infer gene function, and because the zebrafish is a more tractable laboratory vertebrate system than rodents to study disease mechanisms in vivo, clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein-9 nuclease (Cas9) genomic editing was used to delete the ~60-kbp-long zebrafish lrrk2 locus containing the entire open reading frame. Constitutive removal of both the maternal and the zygotic lrrk2 function (mzLrrk2 individuals) causes a pleomorphic phenotype in the larval brain at 5 days post-fertilisation (dpf), including increased cell death, delayed myelination, and reduced and morphologically abnormal microglia/leukocytes. However, the phenotype is transient, spontaneously attenuating or resolving by 10 dpf, and the mutants are viable and fertile as adults. These observations are mirrored by whole-larva transcriptome data, revealing a more than eighteen-fold drop in the number of differentially expressed genes in mzLrrk2 larvae from 5 to 10 dpf. Additionally, analysis of spontaneous swimming activity shows hypokinesia as a predictor of Lrrk2 protein deficiency in larvae, but not in adult fish. Because the catecholaminergic (CA) neurons are the main clinically relevant target of PD in humans, the CA system of larvae and adult fish was analysed on both cellular and metabolic level. Despite an initial developmental delay at 5 dpf, the CA system is structurally intact at 10 dpf and later on in adult fish aged 6 and 11 months. However, monoamine oxidase (Mao)-dependent degradation of biogenic amines, including dopamine, is increased in older fish, possibly suggesting impaired synaptic transmission or a leading cause of cell damage in the long term. Furthermore, decreased mitosis rate in the larval brain was found, in the anterior portion only at 5 dpf, strongly and throughout the whole organ at 10 dpf. Conceivably, lrrk2 may have a more general role in the control of cell proliferation during early development and a more specialised one in the adult stage, possibly conditional, for example upon brain damage. Because the zebrafish can regenerate lost neurons, it represents a unique opportunity to elucidate the endogenous processes that may counteract neurodegeneration in a predisposing genetic background. To this aim, the regenerative potential of the adult telencephalon upon stab injury was tested in mzLrrk2 fish. Indeed, neuronal proliferation was reduced, suggesting that a complete understanding of Lrrk2 biology may not be fully appreciated without recreating challenging scenarios. To summarise, the present results demonstrate that loss of lrrk2 has an early effect on zebrafish brain development that is later often compensated. Nonetheless, perturbed aminergic catabolism, and specifically increased Mao-dependent aminergic degradation, is reported for the first time in a LRRK2 knockout model. Furthermore, a link between Lrrk2 and the control of basal cell proliferation in the brain, which may become critical under challenging circumstances such as brain injury, is proposed. Future directions should aim at exploring which brain cell types are specifically affected by the mzLrrk2 hypoproliferative phenotype and the resulting consequences on a circuitry level, particularly in very old fish (i.e., over 2 years of age).

During gastrulation, a set of highly coordinated morphogenetic movements creates the shape and internal organization of the embryo. In teleostean fishes, these morphogenetic movements involve not only the embryonic progenitor cells (deep cells) but also two extra-embryonic tissues: an outer sheet of epithelial cells (EVL) and a yolk syncytial layer (YSL). Epiboly is characterized by the spreading of the blastoderm (deep cells and EVL) to cover the large yolk cell, whereas convergence and extension leads, respectively, to mediolateral narrowing and anteroposterior elongation of the embryo. Recent studies have shown that the nuclei of the YSL undergo epiboly and convergence and extension movements similarly to the overlying deep cells, suggesting that these tissues interact during gastrulation. However, it is so far not clear whether and how the movements of YSL nuclei and deep cells influence each other. In the first part of this thesis, the convergence and extension movement of YSL nuclei was quantitatively compared to the movement of the overlying mesendodermal progenitor (or “hypoblast)” cells. This revealed that, besides the similarity in the overall direction of movement, YSL nuclei and hypoblast cell movements display differences in speed and directionality. Next, the interaction between YSL and hypoblast was addressed. The movement of the blastoderm was analyzed when YSL nuclei movement was impaired by interfering with the YSL microtubule cytoskeleton. We found that YSL and blastoderm epiboly were strongly reduced, while convergence and extension were only mildly affected, suggesting that YSL microtubules and YSL nuclei movement are required for epiboly, but not essential for convergence and extension of the blastoderm. We also addressed whether blastodermal cells can influence YSL nuclei movement. In maternal-zygotic one-eyed pinhead (MZoep) mutant embryos, which lack hypoblast cells, YSL nuclei do not undergo proper convergence movement. Moreover, transplantation of wild type hypoblast cells into these mutants locally rescued the YSL nuclei convergence phenotype, indicating that hypoblast cells can control the movement of YSL nuclei. Finally, we propose that the hypoblast influences YSL nuclei movement as a result of shape changes caused by the collective movement of cells, and that this process requires the adhesion molecule E-cadherin.

Fluorescence correlation spectroscopy (FCS) is an ultra-sensitive optical technique to investigate the dynamic properties of ensembles of single fluorescent molecules in solution. It is in particular suited for measurements in biological samples. High sensitivity is obtained by employing confocal microscopy setups with diffraction limited small detection volumes, and by using single-photon sensitive detectors, for example avalanche photo diodes (APD). However, fluorescence signal is hence typically collected from a single focus position in the sample only, and several measurements at different positions have to be performed successively. To overcome the time-consuming successive FCS measurements, we introduce electron multiplying CCD (EMCCD) camera-based spatially resolved detection for FCS. With this new detection method, multiplexed FCS measurements become feasible. Towards this goal, we perform FCS measurements with two focal volumes. As an application, we demonstrate spatial cross-correlation measurements between the two detection volumes, which allow to measure calibration-free diffusion coefficients and direction-sensitive processes like molecular flow in microfluidic channels. FCS is furthermore applied to living zebrafish embryos, to investigate the concentration gradient of the morphogen fibroblast growth factor 8 (Fgf8). It is shown by one-focus APD-based and two-focus EMCCD-based FCS, that Fgf8 propagates largely by random diffusion through the extracellular space in developing tissue. The stable concentration gradient is shown to arise from the equilibrium between a local morphogen production and the sink function of the receiving cells by receptor-mediated removal from the extracellular space. The study shows the applicability of FCS to whole model organisms. Especially in such dynamically changing systems in vivo, the perspective of fast parallel FCS measurements is of great importance. In this work, we exemplify parallel, spatially resolved FCS by utilizing an EMCCD camera. The approach, however, can be easily adapted to any other class of two-dimensional array detector. Novel generations of array detectors might become available in the near future, so that multiplexed spatial FCS could then emerge as a standard extension to classical one-focus FCS. / Fluoreszenz-Korrelations-Spektroskopie (FCS) ist eine hochempfindliche optische Methode, um die dynamischen Eigenschaften eines Ensembles von einzelnen, fluoreszierenden Molekülen in Lösung zu erforschen. Sie ist insbesondere geeignet für Messungen in biologischen Proben. Die hohe Empfindlichkeit wird erreicht durch Verwendung konfokaler Mikroskop-Aufbauten mit beugungsbegrenztem Detektionsvolumen, und durch Messung der Fluoreszenz mit Einzelphotonen-empfindlichen Detektoren, zum Beispiel Avalanche-Photodioden (APD). Dadurch wird das Fluoreszenzsignal allerdings nur von einer einzelnen Fokusposition in der Probe eingesammelt, und mehrfache Messungen an verschiedenen Positionen in der Probe müssen nacheinander durchgeführt werden. Um die zeitaufwendigen, aufeinanderfolgenden FCS-Einzelmessungen zu überwinden, entwickeln wir in dieser Arbeit Elektronenvervielfachungs-CCD (EMCCD) Kamera-basierte räumlich aufgelöste Detektion für FCS. Mit dieser neuartigen Detektionsmethode werden Multiplex-FCS Messungen möglich. Darauf abzielend führen wir FCS Messungen mit zwei Detektionsvolumina durch. Als Anwendung nutzen wir die räumliche Kreuzkorrelation zwischen dem Signal beider Fokalvolumina. Sie ermöglicht die kalibrationsfreie Bestimmung von Diffusionskoeffizienten und die Messung von gerichteter Bewegung, wie zum Beispiel laminarem Fluss in mikrostrukturierten Kanälen. FCS wird darüber hinaus angewendet auf Messungen in lebenden Zebrafischembryonen, um den Konzentrationsgradienten des Morphogens Fibroblasten-Wachstumsfaktor 8 (Fgf8) zu untersuchen. Mit Hilfe von APD-basierter ein-Fokus FCS und EMCCD-basierter zwei-Fokus FCS zeigen wir, dass Fgf8 hauptsächlich frei diffffundiert im extrazellulären Raum des sich entwickelnden Embryos. Der stabile Konzentrationsgradient entsteht durch ein Gleichgewicht von lokaler Morphogenproduktion und globalem Morphogenabbau durch Rezeptor vermittelte Entfernung aus dem extrazellulären Raum. Die Studie zeigt die Anwendbarkeit von FCS in ganzen Modell-Organismen. Gerade in diesen sich dynamisch ändernden Systemen in vivo ist die Perspektive schneller, paralleler FCS-Messungen von großer Bedeutung. In dieser Arbeit wird räumlich aufgelöste FCS am Beispiel einer EMCCD Kamera durchgeführt. Die Herangehensweise ist jedoch einfach übertragbar auf jede andere Art von zwei-dimensionalem Flächendetektor. Neuartige Flächendetektoren könnten in naher Zukunft verfügbar sein. Dann könnte räumlich aufgelöste Multiplex-FCS eine standardisierte Erweiterung zur klassischen ein-Fokus FCS werden.

Die Alzheimer-Krankheit ist eine gewaltige Bedrohung für eine alternde Gesellschaft. Millionen von Menschen leben weltweit mit der Alzheimer-Krankheit, für die es keine aktuelle Behandlung gibt. Die Amyloidkaskaden-Hypothese (AKH) ist die aktuell am meisten akzeptierte Hypothese zur Ursache der Alzheimer-Krankheit. Die AKH bietet eine mechanistische Sicht auf die pathologische Kaskade, ausgehend von der Amyloid-Aggregation über die chronische Entzündung bis hin zur TAU-Pathologie. Die Medikamente, die auf der Grundlage der AKH entwickelt wurden, konnten Amyloid-Plaques bei Alzheimer-Patienten entfernen, brachten aber keine Verbesserung der kognitiven Fähigkeiten. Diese Misserfolge legen nahe, dass die Alzheimer-Krankheit nicht nur theoretisch im Rahmen der AKH betrachtet werden kann. Neuere Hypothesen kulminieren die Auswirkungen verschiedener Zelltypen (z.B. neurale Stammzellen, Astrozyten, Oligodendrozyten) auf den Ausbruch der Alzheimer-Erkrankung. Komplexe Rückkopplungs- und Feed-Forward-Mechanismen sind in der Pathophysiologie der Alzheimer-Demenz wahrscheinlich. Das Zusammenspiel zwischen der Pathologie und der Beteiligung anderer Zelltypen macht diese Krankheit multifaktoriell und komplex. Kürzlich zeigten zwei Studien (Moreno-Jimenez et al., 2019; Tobin et al., 2019), dass die Produktion neuer Neuronen im menschlichen Gehirn bei der Alzheimer-Erkrankung dramatisch abnimmt. Eine interessante Hypothese wurde durch diese Studien gestützt: Die pathologisch induzierte Erzeugung neuer Neuronen (regenerative Neurogenese) bei Alzheimer-Patienten könnte helfen, die Pathologie der Alzheimer-Erkrankung rückgängig zu machen. Da die Regenerationsfähigkeit bei Säugetieren entwicklungsmäßig wenig ausgeprägt ist (Tanaka und Ferretti, 2009), kann uns die Untersuchung der Neurodegeneration in einem Modellorganismus mit Regenerationsfähigkeit daher lehren, wie man die Proliferation und Neurogenese neuraler Stammzellen unter pathologischen Bedingungen induzieren kann. Für diese spezielle Frage können uns Modellorganismen mit natürlicher Regenerationsfähigkeit zeigen, wie man Proliferation und Neurogenese unter den pathologischen Bedingungen der Alzheimer-Erkrankung induzieren kann. Der Zebrafisch bietet eine beispiellose Möglichkeit, die Neurodegeneration und Regeneration zu modellieren, um die molekularen Mechanismen zu untersuchen, wie anhand der Neurogenese in Wirbeltiergehirnen die Alzheimer-Krankheit verbessert werden kann. Dies wurde in unserem Labor bereits in mehreren Publikationen gezeigt. Aus diesem Grund habe ich in meiner Doktorarbeit Zebrafische verwendet, um die Plastizität neuraler Stammzellen (NSZ) zu untersuchen. Besonders interessierte mich die Heterogenität von NSZ-Populationen in Bezug auf ihre molekularen Programme und die molekulare Grundlage der regenerativen Neurogenese von NSZ auf das Amyloid-β-42 (Aβ42) und TAU-Pathologien.