Thesis (Ph. D.)--University of Wisconsin--Madison, 1970. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Several genes thought to confer susceptibility to dyslexia have been identified, and the purpose of this study is to 1) determine the expression pattern of one of these gene products and 2) characterize the function of the product of one of these genes, namely KIAA0319-Like (KIAA0319L), using the developing chick visual system as a model. Whole mount in situ hybridization was performed for KIAA0319L on embryonic day (E)3 – E5 and in situ hybridization on sections was performed at later stages. Engineered microRNA (miRNA) constructs targeting KIAA0319L were prepared and their specificity and efficiency for knocking down KIAA0319L were tested. miRNAs were electroporated in E5 optic tecta (OT). Embryos were sacrificed at E12. OT were removed, sectioned and analyzed. Results demonstrate that KIAA0319L is expressed in the developing chick visual system. Knockdown of KIAA0319L in the OT results in abnormal migration indicating that KIAA0319L is necessary for this process.

Several genes thought to confer susceptibility to dyslexia have been identified, and the purpose of this study is to 1) determine the expression pattern of one of these gene products and 2) characterize the function of the product of one of these genes, namely KIAA0319-Like (KIAA0319L), using the developing chick visual system as a model. Whole mount in situ hybridization was performed for KIAA0319L on embryonic day (E)3 – E5 and in situ hybridization on sections was performed at later stages. Engineered microRNA (miRNA) constructs targeting KIAA0319L were prepared and their specificity and efficiency for knocking down KIAA0319L were tested. miRNAs were electroporated in E5 optic tecta (OT). Embryos were sacrificed at E12. OT were removed, sectioned and analyzed. Results demonstrate that KIAA0319L is expressed in the developing chick visual system. Knockdown of KIAA0319L in the OT results in abnormal migration indicating that KIAA0319L is necessary for this process.

Techn. Hochsch., Diss., 2000--Aachen.

Universiẗat, Diss., 2004--Bremen.

Universiẗat, Diss., 2001--Bremen.

xiv, 152 p. Adviser: Terry Takahashi (Biology Dept.). Chapter 2 of this dissertation has been previously published in the Journal of Neurophysiology. Citation: Whitchurch EA and Takahashi TT. Combined auditory and visual stimuli facilitate head saccades in the barn owl (Tyto alba). J Neurophysiol 96: 730-745, 2006. / A print copy of this title is available through the UO Libraries under the call number: SCIENCE QL696.S85 W54 2006 / Survival depends on our ability to detect and integrate sensory information from multiple modalities, allowing for the most efficient behavioral response. For example, barn owls must combine sights and sounds from the environment to localize potential prey. A vole scurrying through a drift of dried leaves is more likely to meet its doom if a nearby owl can both faintly see and hear it. How does the brain take two physically discreet inputs and combine them into a unified representation of the surrounding multisensory world? Moreover, how is this internal representation transformed into the most efficient behavioral response? This dissertation comprises original research addressing these questions in the barn owl with two distinct approaches: First, Chapters II and III describe orientation behavior in response to auditory, visual, and audiovisual stimuli. Chapter II probes the effect of stimulus strength on saccadic behavior and the nature of audiovisual integration, and was taken from a co-authored publication. Chapter III explores the behavioral consequence of an induced stimulus asynchrony in audiovisual integration and was taken from a co-authored manuscript being prepared for publication. The second experimental approach is described in Chapters IV and V. These chapters probe the physiological basis of saccadic behavior by measuring single-neuron responses to auditory, visual, and audiovisual stimuli. Chapter IV describes how auditory responses of neurons from the external nucleus of the inferior colliculus depend on sound pressure level. Chapter V describes activity of optic tectum neurons in response to auditory, visual, and audiovisual stimuli. The behavioral findings described herein suggest that barn owls often incorporate both the speed of the auditory system and the accuracy of the visual system when localizing a multisensory stimulus, even when the two modalities are presented asynchronously. The physiological studies outlined in this dissertation show that sensory representations in the midbrain can be used to predict general trends in saccadic behavior: Neuronal thresholds were within the range of observed behavioral thresholds. Responses to multisensory stimuli were enhanced relative to unisensory stimuli, possibly corresponding to enhanced multisensory behavior. These data support fundamental rules in multisensory integration that may apply across species.

Psychostimulants are known to alter visual function acutely and on withdrawal, and can cause attention deficit following prenatal exposure. However, psychostimulants can also improve visual attention in patients with attention deficit. The mechanisms involved in these contrasting effects remain largely unknown. To determine the role of specific brain regions and the dopamine system in the impact of cocaine exposure on visual processing, we employed two-photon microscopy and a transgenic larval zebrafish expressing the calcium indicator GCaMP-HS. We documented neuronal responses to contrasting visual stimuli, red light (LF) and dark (DF) flashes. We found that in the optic tectum neuropil (TOn), both stimuli elicited similar responses, though after repeated stimulus presentation, habituation developed to dark flash only. The dorsal telencephalon (dTe) responded and habituated to LF only. Acute cocaine (0.5 μM) reduced neuronal responses to LF in both brain regions and prevented habituation of dTe neurons to LF, but did not modify responses or habituation to dark flash. Prenatal cocaine exposure (PCE) did not modify baseline responses, but it prevented the acute effects of cocaine on LF responses in both regions and habituation in dTe, with no impact on dark flash responses. PCE also significantly reduced D1 dopamine receptor expression in TOn and cerebellum, but not dTe or the eye. Fish lacking the dopamine transporter (DATKO) retained normal D1 expression throughout the brain, baseline responses to LF in both TOn and dTe, and response reduction following cocaine in TOn. However, they demonstrated abnormal swimming behavior, and neither their swimming behavior nor dTe responses to LF were modified by cocaine. We discovered that in zebrafish, a diurnal vertebrate, responses to light not only require the primary visual processing center TO (superior colliculus in mammals), but also higher level processing by dTe. Responses to light but not darkness are modified by cocaine, unless the fish lack DAT or were exposed to PCE. Together, our results demonstrate specific effects of cocaine on visual processing mediated by the dopamine system, and provide a novel animal model for further investigation of these phenomena and development of new therapeutic approaches.

Light and electron microscopic degeneration studies were used to examine the telencephalotectal pathway in goldfish. Both techniques showed that each telencephalic lobe sent bilateral projections to several tectal laminae. Degenerating synaptic terminals and fibers were observed in the major retinal projection lamina as well as in other tectal laminae. The terminals contained round to oval synaptic vesicles, asymmetric synapses and contacted relatively small postsynaptic profiles.

L’identité des cellules souches et des progéniteurs neuraux, comme celle de tout type cellulaire, est caractérisée par des signatures moléculaires spécifiques qui dépendent de l’environnement dans lesquelles les cellules se trouvent. Ainsi, il est primordial d’étudier ces cellules dans un contexte in vivo. Le toit optique du poisson zèbre est un modèle idéal pour ce type d’étude. En effet, c’est une large partie du cerveau moyen localisée en position dorsale et qui présente la particularité de croitre de manière orientée tout au long de la vie de l’animal grâce aux cellules neuroépitheliales présentes à sa périphérie (dans la « peripheral midbrain layer », PML). De plus, les progéniteurs neuroépithéliaux, les progéniteurs lents et les cellules post-mitotiques sont localisées dans des domaines adjacents du toit, conséquence de sa croissance orientée. Chaque population cellulaire est marquée par des profils d’expression particuliers. Ainsi, une recherche dans la base de données ZFIN nous a permis d’identifier environ 50 gènes ayant une forte expression dans les cellules de la PML (progéniteurs neuroépithéliaux). De façon intéressante, beaucoup de « gènes PML » codent pour des facteurs de la biogenèse des ribosomes. L’accumulation de ce type de transcrits dans les progéniteurs lents était surprenante. Ainsi, au cours de mon doctorat, j’ai étudié le rôle spécifique des facteurs de la biogenèse des ribosomes dans le maintien des cellules neuroepithéliales de la PML. En effet, bien qu’il soit généralement admis que la biogenèse des ribosomes est un processus essentiel dans toutes les cellules, il a été récemment démontré que plusieurs facteurs nécessaires à la synthèse des ribosomes ont un rôle tissu-spécifique. Par exemple, Notchless est requis pour la survie de la masse cellulaire interne de l’embryon préimplantatoire de souris. Récemment, des expériences de knock-out conditionnel chez la souris ont montré que Notchless était nécessaire au maintien des cellules souches hématopoïétiques et intestinales, mais pas à celui des cellules différenciées. En effet, en absence de Notchless dans les cellules souches, la grosse sous-unité ribosomique (60S) ne peut pas être exportée hors du noyau et s’accumule. Au contraire, dans les cellules différenciées, où Notchless n’est pas indispensable, cette accumulation n’est pas observée. J’ai commencé une étude fonctionnelle basée sur la surexpression conditionnelle de la forme dominante-négative du gène notchless homolog 1 (nle1, homologue poisson zèbre du gène Notchless mammifère). Selon mon hypothèse, les progéniteurs lents de la PML (Slow amplifying progenitors, SAPs) pourraient avoir besoin de Notchless pour la maturation de la sous-unité 60S, contrairement aux cellules différenciées qui pourraient survivre après la délétion de ce gène. Des expériences sont encore en cours, mais nous avons déjà pu démontrer que nle1 joue un rôle crucial dans la survie des progénitéurs neuroépithéliaux de la PML. En parallèle, j’ai étudié des lignées de poisson-zèbre mutantes pour des gènes codants pour des composants du complexe de snoRNP (box C/D small nucleolar ribonucleoprotein : Fibrillarine, Nop56, Nop58). Les trois mutants présentent des phénotypes similaires, en particulier une apoptose massive et une dérégulation du cycle cellulaire dans l’ensemble du toit optique à 48 heures de développement. Étonnamment, ces résultats sont en faveur d’un arrêt du cycle cellulaire à la transition G2/M. Ainsi, cette étude pourrait permettre de mettre en évidence de nouveaux mécanismes d’arrêt du cycle cellulaire lors de défauts de biogenèse des ribosomes. L’ensemble de ces résultats montrent comment les facteurs de la biogenèse des ribosomes (tout comme le processus) contribue à la régulation fine de l’homéostasie cellulaire, et donc à la détermination de l’identité des cellules progénitrices. / In neural stem cells (NSCs) and neural progenitors (NPs), as in other cell types, cell identity is characterized by specific molecular signatures that depend on the environment provided by neighboring cells. Thus, it is important to study progenitor cells in vivo. The zebrafish optic tectum (OT) is a suitable model for that purpose. Indeed, this large structure of the dorsal midbrain displays life-long oriented growth supported by neuroepithelial cells present at its periphery (in the peripheral midbrain layer, PML). Moreover, neuroepithelial progenitors, fast-amplifying progenitors and post-mitotic cells are found in adjacent domains of the OT, as a consequence of its oriented growth. Each cell population is marked by concentric gene expression patterns. Interestingly, a datamining of the ZFIN gene expression database allowed us to identify around 50 genes displaying biased expression in PML cells (neuroepithelial progenitors). Interestingly, many “PML genes” code for ribosome biogenesis factors. The accumulation of transcripts for such ubiquitously expressed genes in SAPs was very surprising so during my thesis I examined whether ribosome biogenesis may have specific roles in these neuroepithelial cells, while improving our knowledge. Indeed, although it is generally admitted that ribosome biogenesis is essential in all cells, it has been shown quite recently that several components of the ribosome biogenesis have tissue restricted roles. For example, Notchless is required for the survival of the inner cell mass in the preimplantation mouse embryo. More recently, conditional knock-out experiments in mice showed that Notchless is necessary for the maintenance of hematopoietic stem cells and intestinal stem cells, but not for committed progenitors and differentiated cells. Indeed in the absence of Notchless in stem cells, the immature 60S subunit cannot be exported from the nucleus and accumulates. This does not happen in differentiated cells where Notchless is dispensable. I started a functional study based on the conditional overexpression of a dominant-negative form of the gene notchless homolog 1 (nle1, the zebrafish homolog of the mammalian gene Notchless). My hypothesis was that the PML slow-amplifying progenitors (SAPs) may require Notchless for the maturation of the 60S subunit, but not the differentiated cells which could survive also after the deletion of this gene. Experiments are still underway. So far we could demonstrate that nle1 has a crucial role in SAPs. I studied zebrafish mutants for genes coding for the components of the box C/D small nucleolar ribonucleoprotein (snoRNP) complex (Fibrillarin, Nop56, Nop58). Mutants displayed a similar phenotype with massive apoptosis and a deregulation of the cell cycle in the whole tectum at 48hpf. Our data suggest a cell cycle arrest at the G2/M transition, highlighting novel possible mechanisms of cell cycle arrest upon impaired ribosome biogenesis. All together, these data highlight how ribosome biogenesis factors and the whole ribosome biogenesis contribute to the fine regulation of cell homeostasis thereby contributing to the determination of progenitor cell identity.