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Prenatal exposure to Zika virus (ZIKV) can result in microencephaly and congenital Zika syndrome but why some brain cells and structures are initially spared by the virus is unknown. Here, a novel murine model of ZIKV infection incorporating in utero electroporation with cell type specific promotors was used to identify the time course of ZIKV infection and to determine which neural precursor cells are initially infected or spared. In vivo time course studies revealed early presence of ZIKV in apical radial glial cells (aRGCs) while infection of basal intermediate progenitor cells climbed after three days of virus exposure. ZIKV-exposed fetal brains exhibited microencephaly as early as 1 day post injection, caused by apoptosis and reduced proliferation, and this change in brain size persisted until birth regardless of developmental age at infection. During infection, 60% of aRGC basal fibers were perturbed while 40% retained normal morphology, indicating that aRGCs are not uniformly vulnerable to ZIKV infection. To evaluate this heterogeneous vulnerability, we generated cell type-specific fate mapping plasmid probes using a previously published single cell RNA-Seq dataset on the E15.5 mouse neocortical wall. The results indicate that one class of aRGC preferentially expresses the putative ZIKV entry receptor AXL, and that these cells are more vulnerable to ZIKV infection than the other aRGC subtypes with low AXL expression. Together, these data highlight important temporal and cellular details of ZIKV fetal brain infection and may be important for prevention strategies and for management of congenital Zika syndrome.

Parkinson's disease (PD) is the second most prevalent age-related neurodegenerative disease and currently affects over 8 million people worldwide. The primary features of PD include cognitive, behavioral, and motor function deficits induced primarily by the progressive loss of dopaminergic neurons within the substantia nigra of the basal ganglia (BG). Motor coordination becomes severely affected over the course of the disease, causing patients to experience tremors at rest, bradykinesia, and body rigidity. The availability of treatment options has increased the quality of life for patients experiencing the early stages of PD; however, there exists no cure and treatment options are limited for those experiencing severe, advanced disease symptoms. Genetic studies in PD patients have led to the identification of causative genes, but revealed that less than 20% of cases can be attributed to monogenic variations. Evidence strongly indicates that the majority of PD cases are idiopathic and likely driven due to gene by environmental interactions. Reflective of this idea, recent research efforts have turned to genome-wide association studies (GWAS) to provide indications of gene variations, that while not causative of PD, incur increased risk within patient populations. GWAS findings play a particularly crucial role in neurodegenerative interventions, as early identification of patient risk may allow for preventative therapeutics to delay disease onset or reduce symptom severity. Amongst the many gene variants identified as incurring increased PD risk, single-nucleotide polymorphisms (SNPs) in the loci for CD38 that cause reduced gene expression are consistently identified as increasing risk. The cluster of differentiation 38 (CD38) protein serves two major roles: one as a receptor for immunological response and a second as an ectoenzyme that modulates bioenergetic functions. The particular functions of CD38 are highly relevant to neurodegenerative contexts, as changes in central nervous system (CNS) inflammatory status and means of cellular energy production typically precede pathological indications. In the brain, CD38 expression is most enriched in astrocytes in BG regions, including substantia nigra, midbrain, and striatum. However, it is not known how CD38 deficiency may contribute to astrocytic dysfunction and neuropathological features of PD. This dissertation describes how CD38 influences astrocytic gene expression and cellular bioenergetics. Astrocyte RNA was sequenced from the BG of one-year old male Cd38+/+, Cd38+/-, and Cd38-/- mice by magnetic-activated cell sorting (MACS) to acquire astrocyte isolates. Numerous differentially expressed genes (DEGs) were identified in Cd38 Cd38+/- and Cd38-/- astrocytes that relate to regulation of cellular health, responses to stress, and bioenergetic functions. GO analysis further suggested mitochondrial dysfunction in both Cd38+/- and Cd38-/- astrocytes. In a subsequent set of experiments evaluating mitochondrial function by Seahorse XF96 platform, Cd38+/- and Cd38-/- astrocytes displayed altered bioenergetic function. The results herein demonstrate that astrocytic Cd38 expression regulates cellular function and implicates transcriptional changes associated with the hallmarks of neurodegeneration. These findings serve to provide future direction for studies evaluating the relationship between CD38 function and astrocytes as it relates to neurodegenerative PD risk. / Doctor of Philosophy / Parkinson's disease (PD) is the second most common age-related neurodegenerative disease and currently affects over 8 million people worldwide. The primary features of PD include cognitive, behavioral, and motor function deficits induced primarily by the progressive loss of specialized neurons within the substantia nigra of the basal ganglia (BG) brain region. Motor coordination becomes severely affected over the course of the disease, causing patients to experience body tremors, slowness, and rigidity. The availability of treatment options has increased the quality of life for patients experiencing the early stages of PD; however, there exists no cure and little treatment options for those experiencing severe, advanced disease symptoms. Genetic studies in PD patients have led to the identification of causative genes, but revealed that less than 20% of cases can be attributed to specific, individual variations. Evidence strongly indicates that the majority of PD cases are likely caused by small gene changes that interact with environmental factors. Recent research efforts have turned to genome-wide association studies (GWAS) to identify these small changes, that while not causative of PD, may increase risk within patient populations. GWAS findings play a particularly crucial role in treating neurodegenerative diseases, as early identification of patient risk may allow for preventative therapeutics to slow disease onset or reduce symptom severity. Amongst the many small gene changes identified as increasing PD risk, changes in the gene CD38 that cause reduced gene expression are consistently identified as increasing risk. The cluster of differentiation 38 (CD38) protein serves two major roles: one as a receptor for immune responses and a second as an enzyme that impacts how cells produce energy. The functions of CD38 are highly relevant to neurodegenerative contexts, as changes in central nervous system (CNS) inflammatory status and means of cellular energy production typically precede disease pathology. In the brain, CD38 expression is most enriched in astrocytes, specialized brain cells that supports neurons, in regions affected by PD. However, it is not known how CD38 deficiency may contribute to astrocytic dysfunction and neuropathological features of PD. This dissertation describes how CD38 influences astrocytic gene expression and cellular bioenergetics. Astrocyte RNA was sequenced from the BG of one-year old male Cd38+/+, Cd38+/- (50% CD38 loss), and Cd38-/- (100% CD38 loss) mice by magnetic-activated cell sorting (MACS) to acquire astrocytes. Numerous changes in gene expression were identified in Cd38 Cd38+/- and Cd38-/- astrocytes that relate to regulation of cellular health, responses to stress, and energy functions. Further analysis looking at functions, suggested mitochondrial abnormalities in both Cd38+/- and Cd38-/- astrocytes. In a subsequent set of experiments evaluating mitochondrial function by Seahorse XF96 platform, Cd38+/- and Cd38-/- astrocytes displayed altered energetic function. The results herein demonstrate that astrocytic Cd38 expression regulates cellular function and implicates transcriptional changes associated with the hallmarks of neurodegeneration. These findings serve to provide future direction for studies evaluating the relationship between CD38 function and astrocytes as it relates to neurodegenerative PD risk.

Several cell lineages derived from the mesectoderm occupy and contact axons in the midline of the developing Drosophila CNS. Which of these midline cell lineages contribute to commissural axon morphogenesis? In the absence of the midline cells as in mutant embryos of the single-minded gene, the longitudinal axons collapse at the midline and commissural axons are absent. Despite the similarity in axon tract phenotype, the midline cells in slit mutant embryos survive but are displaced. Correct cytoarchitecture of the midline cells is therefore dependent on the activity of Sli protein which is in turn necessary for commissure formation. In mutant embryos displaying a fused commissure phenotype (rhomboid and Star), the anterior and middle midline glia cells failed to migrate and died by apoptosis after commissure development. In these mutants the number of cells in midline neuronal lineages was reduced before defects in midline glia were apparent. In wildtype embryos approximately 50% of cells in three midline glia lineages died by apoptosis after commissure separation as shown by ultrastructural and enhancer trap analysis. Midline glia lineages died by apoptosis as shown morphologically and by their survival in embryos deficient in the cell death gene reaper. Quantitative analysis revealed variable survival of cells in the anterior, middle and posterior midline glial lineages during embryogenesis suggesting heterogeneity among these cells. The presence of extra anterior, middle and posterior midline glial lineages relative to wildtype numbers in reaper mutant embryos suggested that cell death regulates either midline glial proliferation or cell fate determination during wildtype embryogenesis. Alterations in axon-glia contact correlated with changes in midline glia survival. What happens to apoptotic cells in the Drosophila embryonic central nervous system? A variety of glia in the nervous system were capable of phagocytic activity including midline glia, longitudinal tract glia, nerve root glia and subperineurial glia, revealed by electron microscopy. However, the majority of apoptotic cells in the central nervous system were engulfed by subperineurial glia. In the absence of phagocytic haemocytes in embryos mutant for the Bicaudal-d gene, most apoptotic cells were retained in subperineurial glia at the outer edges of the central nervous system. Apoptotic cells were expelled from the central nervous system of Bicaudal-d mutant embryos suggesting that phagocytic haemocytes participate in the removal of apoptotic cells from the central nervous system but are not essential for this process. / Thesis / Doctor of Philosophy (PhD)

京都大学 / 新制・課程博士 / 博士(生命科学) / 甲第24985号 / 生博第514号 / 新制||生||68(附属図書館) / 京都大学大学院生命科学研究科高次生命科学専攻 / (主査)教授 北島 智也, 教授 見学 美根子, 教授 今吉 格 / 学位規則第4条第1項該当 / Doctor of Philosophy in Life Sciences / Kyoto University / DFAM

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Astrozyten erfüllen unverzichtbare Aufgaben im ZNS. Sie sorgen im Normalfall unter anderem für eine ausgewogene K+/H2O-Clearence, regulieren den Gefäßdurchmesser, bilden die Blut-/Hirnschranke, betreiben “Transmitter-Recycling” und modulieren die interneuronale Signalweitergabe durch prä- und postsynaptische Mechanismen. Die Funktionen und Einflüsse dieser zentralnervösen Gliazellen unter pathologischen Bedingungen im ZNS sind bei weitem nicht so gut untersucht, aber ebenso vielfältig. Eine ganz entscheidende Frage stellt sowohl unter physiologischen wie auch pathologischen Bedingungen das Vorliegen eines Überlappungsfaktors des von benachbarten Astrozyten okkupierten Areals dar. Betrüge ein solcher Faktor ! 1, könnten mehrere Gliazellen das gleiche Areal auch unter pathologischen Bedingungen durch ihre vielfältigen Funktionen unterstützen. Dahingegen würde das Ausbleiben eines Überlappungsgrades ! 1 bedeuten, dass bestimmte Gebiete im Neuropil anfälliger gegen Noxen oder degenerative Veränderungen wären. Um diesen Überlappungsgrad zu untersuchen, wurden Hirnschnitte von Labormäusen mittels einer geeigneten Methodenkombination untersucht. Dabei wurde das durchschnittliche Volumen der Astrozyten im motorischen Kortex durch Golgi- Färbung, sowie deren Zellzahl pro Volumeneinheit durch immunhistochemische Färbungen untersucht und mittels konfokaler Laserscanning-Mikroskopie dokumentiert. Aus diesen Parametern ließ sich ferner der durchschnittliche Überlappungsfaktor im beschriebenen Areal berechnen. Im Interesse dieser Arbeit standen dabei neben dem Unterschied im Überlappungsfaktor der Astrozyten zwischen Wildtyp- und GFAP-/- VIM-/- Knockout- Mäusen, als Beispiel für ein genetisch bedingtes Fehlen dieser Intermediärfilamente, auch der Einfluss des fortschreitenden Lebensalters, so dass für beide Genotypen sowohl junge- als auch alte Tiere untersucht wurden. Folgende Ergebnisse lassen sich zusammenfassen: 1. Das Vorhandensein der Intermediärfilamente GFAP und Vimentin scheint keinen Einfluss auf das Volumen der Astrozyten im motorischen Kortex zu haben. 2. Das Lebensalter der V ersuchstiere steht mit dem V olumen der Astrozyten signifikant in Zusammenhang. Das von Astrozytenfortsätzen der knapp zwei Jahre alten Tiere okkupierte Volumen betrug mit durchschnittlich ca. 61.000 !m3 gut das Doppelte des Volumens in jungen Mäusen (ca. 28.000 !m3). 3. Die Zellzahl der Astrozyten im motorischen Kortex wird offenbar weder vom Lebensalter, noch vom Vorhandensein der Intermediärfilamente GFAP und Vimentin signifikant beeinflusst. 4. Der Überlappungsfaktor der Astrozyten im motorischen Kortex lag bei den jungen Kontroll-Tieren bei 0,87 und bei den jungen DKO-Tieren bei 0,96. 5. Der Überlappungsfaktor der Astrozyten im motorischen Kortex lag bei den alten Kontroll-Tieren bei 2,22 und bei den alten DKO-Tieren bei 2,10. Die Ergebnisse zeigen, dass das Fehlen der Intermediärfilamente GFAP und Vimentin keinen Einfluss auf den Überlappungsgrad der Astrozyten im motorischen Kortex hat. Die Ursache für phänotypisch manifeste Erkrankungen, wie z.B. der Alexander Krankheit, welche durch ein fehlerhaft exprimiertes GFAP in Astrozyten hervorgerufen wird, ist demnach in anderen Mechanismen zu suchen. Großen Einfluss auf den Überlappungsfaktor der Astrozyten hatte dagegen das Lebensalter der Versuchstiere, was sich mit neueren Erkenntnissen zur Funktion der Astrozyten im Hinblick auf Lernvorgänge, aber auch auf degenerative Prozesse, in Zusammenhang bringen lässt.:BIBLIOGRAPHISCHE BESCHREIBUNG 1 INHALTSVERZEICHNIS 2 VERZEICHNIS DER ABKÜRZUNGEN 5 1. EINLEITUNG UND FRAGESTELLUNG 6 1.1 Das ZNS / Der Kortex 6 1.2 Gliazellen 9 1.2.1 Astrozyten 10 1.2.1.1 Morphologie / Morphometrie 10 1.2.1.2 Funktionen 12 1.2.1.3 reaktive Astrozyten 13 1.3 Intermediärfilamente 14 1.3.1 Funktionen 17 1.3.2 Intermediärfilamente und Zellwachstum 18 1.4 Ziel der Arbeit 19 2. MATERIAL UND METHODEN 24 2.1 Die Versuchstiere 24 2.2 Golgi-Färbungen 25 2.3 Immunhistochemische Färbungen 26 2.3.1 Die indirekte Nachweismethode 27 2.4 Das konfokale Mikroskop 28 2.5 Mikroskopische Untersuchung 30 2.5.1 Untersuchung der Volumina 30 2.5.2 Untersuchung der Zellzahlen 32 2.6 Bildauswertung 34 2.6.1 Volumenmessung / Golgi-Präparate 34 2.6.2 Zellzahl / Immunhistochemie 37 2.7 Berechnungen / Überlappungsfaktor / Statistische Auswertung 38 3. ERGEBNISSE 40 3.1 Volumina der Astrozyten 40 3.2 Zellzahl der Astrozyten 45 3.3 Der Überlappungsfaktor 48 3.4 Zusammenfassung 51 4. DISKUSSION 52 4.1 Kritik an der Methodik 52 4.1.1 Golgi-Färbungen zur Volumenmessung 52 4.1.2 S100-ß als Marker zur Zellzahl-Bestimmung 53 4.1.3 Schrumpfung der Präparate 54 4.2 Einordnung der Ergebnisse in die Literatur / Schlussfolgerungen 56 5. ZUSAMMENFASSUNG 60 6. LITERATUR 64 SELBSTSTÄNDIGKEITSERKLÄRUNG 68 LEBENSLAUF 69 DANKSAGUNG 71