No description available.

published_or_final_version / Biochemistry / Doctoral / Doctor of Philosophy

published_or_final_version / Molecular Biology / Master / Master of Philosophy

No description available.

No description available.

No description available.

Axons are directed along stereotypic pathways to their targets by cues arrayed in the extracellular environment. Identifying the cellular and molecular nature of these signals is of high interest and the developing optic pathway is a useful model system for achieving this. Although previous studies have identified several molecules essential for optic pathway formation, in vivo only subsets of retinal axons rely on them. I focused on the Dscam (Down’s syndrome cell adhesion molecule) and Sidekick (Sdk) cell adhesion molecules for potentially playing crucial roles in this system. In situ hybridisation in the embryonic mouse visual system showed Dscam and Sdk-1 expression in the RGC layer of the retina, along the optic pathway and in the visual targets. Sdk-2 was detected in the glia of the optic nerve and optic chiasm, marking the pathway that RGC axons follow, but not in RGCs. No DscamL1 was detected in RGCs or the optic pathway at the stages investigated and it was discounted from future analysis. In vitro, DSCAM promoted RGC axon outgrowth, whereas SDK 1 was inhibitory. SDK 2 had no effect on RGC axon outgrowth, suggesting it does not play a direct role in their pathfinding. Repeating this assay using retinal explants from the Dscamdel17 mouse mutant, showed that DSCAM enhanced retinal axon outgrowth, at least in part, through homophilic interactions. Analysis of visual system development in Dscam mutants showed DSCAM involvement in RGC axon fasciculation and in enhancing their growth, particularly within the ipsilateral optic tract. Retinal cell counts revealed that DSCAM played diverse roles in controlling cell number. Pre- and postnatal retinas lacking DSCAM contained more RGCs and mitotic cells. Postnatally, Dscam-/- retinas also show decreased cell death. In many cases, defect severity was dose-dependent, with an intermediate phenotype in the heterozygous mice, implicating DSCAM in the neurological defects of Downs’ Syndrome patients.

Thesis (M. Sc.)--York University, 2002. Graduate Programme in Kinesiology and Health Science. / Typescript. Includes bibliographical references (leaves 74-82). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004 & res_dat=xri:pqdiss & rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation & rft_dat=xri:pqdiss:MQ71602.

Ovarian cancer is the most lethal gynecological cancer. This is mainly due to widespread peritoneal dissemination and malignant ascites, in which angiogenesis, the formation of new blood vessels, is critical to both ascites development and its metastasis. Loss of E-cadherin is a well-established marker that characterizes the progression of metastatic tumors, including ovarian cancer. The release of a soluble form of E-cadherin (sE-cad) has been frequently associated with a rapid reduction of functional E-cadherin at the cell surface. Importantly, sE-cad is significantly present in ascites from women with stage III/IV ovarian cancer when compared to women with benign ovarian cysts. However, despite the clinical significance, most studies have focused on its role in weakening cell-cell adhesion, whether sE-cad itself has any biological function is not fully understood. Here it is shown for the first time a potent angiogenic role for sE-cad released from ovarian carcinoma. Soluble form of E-cadherin promoted the migration, permeability, and tubulogenesis of endothelial cells. These activities were also observed with a sE-cad/Fc chimera, and targeted inhibition using E-cadherin blocking antibodies completely prevented the sE-cad mediated effects. In addition, it was further revealed that sE-cad could be released from ovarian cancer cells in form of exosomes, a form of extracellular vesicles that play an important role in distant intercellular communication. sE-cad-positive exosomes were able to stimulate the angiogenic phenotype in vitro and functional neovascularization in a Matrigel implant model in vivo. The use of E-cadherin blocking antibodies resulted in diminished angiogenesis, confirming that the effect was sE-cad-positive exosomes specific. In search of the underlying mechanism by which sE-cad-positive exosomes promoted angiogenesis in endothelial cells which lacked E-cadherin, sE-cad was found to heterodimerize with VE-cadherin. This effect was associated with constitutive activation of phosphatidylinositol 3-kinase (PI3K)/Akt and its effector β-catenin, but not p120 catenin. Similarly, the angiogenic phenotype could be reversed by inhibition of VE-cadherin, PI3K/Akt and β-catenin. A mass spectrometric proteomic analysis of the isolated exosomes revealed distinct membrane-bound proteases, especially disintegrin and metalloproteinase 10 (ADAM10) and matrix metalloproteinase 25 (MMP25) commonly associated with ovarian cancer progression, are implicated in sE-cad production. Small interfering RNA-mediated down-regulation of ADAM10 and MMP25 significantly inhibited sE-cad production. Moreover, hepatocyte growth factor, a multifaceted cytokine which is frequently elevated in ovarian cancer ascites, was shown to increase the expression of ADAM10 and MMP25 concomitant with an elevated level of sE-cad. Together, these results uncover a novel angiogenic role of sE-cad and a new mechanism of the action of sE-cad in tumor progression. / published_or_final_version / Biological Sciences / Doctoral / Doctor of Philosophy

published_or_final_version / abstract / toc / Surgery / Master / Master of Philosophy