京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第21954号 / 医博第4496号 / 新制||医||1037(附属図書館) / 京都大学大学院医学研究科医学専攻 / (主査)教授 渡邉 大, 教授 伊佐 正, 教授 椛島 健治 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

京都大学 / 0048 / 新制・課程博士 / 博士(医科学) / 甲第18904号 / 医科博第60号 / 新制||医科||4(附属図書館) / 31855 / 京都大学大学院医学研究科医科学専攻 / (主査)教授 小柳 義夫, 教授 吉村 長久, 教授 髙橋 淳 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第20994号 / 医博第4340号 / 新制||医||1027(附属図書館) / 京都大学大学院医学研究科医学専攻 / (主査)教授 鈴木 茂彦, 教授 伊佐 正, 教授 大森 孝一 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

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The development of the vertebrate eye is tightly controlled by precise genetic regulations. From a single ocular primordium to bilateral eyes with complex structures and cell types, it requires intensive proliferation and migration for cells in both the ectoderm and mesoderm to accomplish ocular morphogenesis, and during this process cell differentiation and interaction takes place to establish the complex composition of ocular cell types and cellular connections. Genetic defects can lead to severe abnormalities in eye morphogenesis and cell differentiation during ocular development. A tremendous amount of work has been done to identify both intrinsic and extrinsic factors that regulate ocular development. However, much more work is needed to fully understand this complex process. Sox4 is known as a transcription activator that regulates cell survival and differentiation in multiple embryonic tissues during development. Evidence of its requirement during ocular development has recently emerged, but the mechanism by which Sox4 regulates ocular development is far from elucidated. Chapter 1 of this dissertation provides an overview of different stages in embryonic eye development and known genetic interactions during each stage. It also reviews recent knowledge about SoxC proteins and their roles in ocular development. Chapter 2 presents data characterizing the expression profile of the zebrafish sox4 co-orthologs, sox4a and sox4b, in the developing eye. Additionally, it presents data from morpholino-mediated sox4 knockdown in zebrafish, which indicate that Sox4 deficiency leads to defects in choroid fissure closure through elevation in the Hedgehog (Hh) signaling pathway. Sox4 knockdown causes upregulation of the Hh ligand indian hedgehog b (ihhb), which alters the proximal-distal boundary of the optic vesicle and inhibits choroid fissure closure. Chapter 3 presents data reporting the generation of sox4 mutant zebrafish lines using the CRISPR/Cas9 genome editing system. Characterization of one sox4a maternal zygotic (MZ) mutant line confirms Sox4’s role in negative regulation of Hh signaling and reveals new evidence that maternal and zygotic sox4 are both critical for ocular development. Chapter 4 presents data demonstrating that sox4 is required for rod photoreceptor neurogenesis. Rod photoreceptor terminal differentiation is delayed in both sox4 morphants and sox4 CRISPR mutants, while rod progenitor and precursor cells are properly specified. In Chapter 5, the roles of Sox4 in regulating ocular development are summarized based on the results, and implications of the results are discussed to expand our understanding of the genetic regulation of ocular morphogenesis and retinal neurogenesis.

ABSTRACT RATE-LIMITING STEP OF CONE PHOTOTRANSDUCTION RECOVERY AND OGUCHI DISEASE MECHANISMS By Frank Sungping Chen Advisor: Ching-Kang Jason Chen, Ph.D. Retinal photoreceptors provide the first gateway in which light information from the environment is transformed into neuronal signals. The cone and rod photoreceptors are responsible for day and night vision, respectively. Understanding rod and cone phototransduction is to figure out how these cells differ in their temporal and spatial sensitivities to allow perception of a broad dynamic range of stimuli. Phototransduction is mediated through a Gprotein signaling cascade. Light absorption by visual pigment triggers the isomerization of 11- cis-retinal covalently attached to these pigments, which are heptahelical transmembrane Gprotein- coupled receptors. Isomerization of 11-cis-retinal to all-trans-retinal activates the receptor, which catalyzes the exchange of GDP for GTP on the α subunit of heterotrimeric Gprotein called transducin. Activated transducin relieves inhibitory constraint on cGMP-PDE, leading to rapid hydrolysis of cGMP, closure of cGMP gated cation channels, and membrane hyperpolarization. In order for photoreceptor to be responsive to light again, this robust phototransduction pathway must be deactivated in a timely fashion and this involves several reactions simultaneously. First, the activated opsin must be phosphorylated by G-protein-coupled receptor kinases (GRKs) and capped by arrestin binding. Second, activated transducin must hydrolyze bound GTP through intrinsic GTPase activity, which is accelerated by a GTPase accelerating protein (GAP) complex comprised of RGS9-1/Gβ5-L/R9AP. Mutations in human genes involved in these reactions cause various visual defects. Cone, by and large, uses the same set of genes for pigment and transducin deactivations but it has lower sensitivity and faster kinetics than rod and is responsible for high visual acuity. During phototransduction recovery in which multiple reactions take place, the slowest reaction will determine the overall rate of recovery. In rod, this so-called, rate-limiting step has been determined to be transducin deactivation. It is unknown whether cone transducin deactivation also controls the timing of conerecovery, although we and others have shown that cone possesses a higher level of GAP concentration. In this thesis, the rate-limiting step in cone phototransduction recovery has been unequivocally determined by overexpressing RGS9-1 by 2.7 fold in mouse cones, which results in accelerated cone recovery. Complementarily, we find that ectopically expressing a human cone opsin kinase GRK7 in mouse cones does not affect cone recovery. These results altogether demonstrate that the rate-limiting step of cone recovery is the GTP-hydrolysis of cone transducin, not the opsin phosphorylation by GRKs. By elucidating the rate-limiting step of photoreceptor recovery, we have revealed the importance of G-protein cycling in timing of both rod and cone photoreceptors. This may further be generalized to other physiological processes controlled by heterotrimeric G-proteins. The proper shutoff of phototransduction is essential for normal vision as recovery defects lead to visual impairment. Even though the reaction catalyzed by GRK1 is not rate-limiting, mutations of this important gene render rhodopsin phosphorylation and deactivation the slowest step in rod recovery and create a pathological condition. GRK1 mutations have been found in Oguchi disease patients, who suffer from congenital stationary night blindness. One of the mutations, V380D, is investigated in detail in this study. Transgenic expression of GRK1 V380D mutant in rods reveals a kinase with reduced expression and catalytic activity. While V380D GRK1 is found capable of inactivating rhodopsin, the reduction in kinase activity leads to a delayed dark adaptation, and is congruent with the night blindness phenotype observed in Oguchi disease patients. Finally, we have also investigated the role of post-translational isoprenylation on GRK1 function. We found that isoprenylation is required for GRK1 membrane association and outer segment targeting. Altogether our data add significantly to understanding the structure and function of GRK1, which is one of the least understood molecules involved in vertebrate phototransduction.