Beyond oxygen and nutrients: Regulatory roles of vascular endothelial cells for normal retinal neurogenesis in zebrafish embryos

Vertebrate retina is one of the most metabolically active tissues in the body and is extremely vascularized to ensure constant supply of oxygen (Alvarez et al. 2007; Wangsa-Wirawan & Linsenmeier 2003). Numerous studies have been conducted to understand the interactions between blood vessels of the eye and different retinal pathologies associated with ocular vasculature. However, interactions between the endothelial cells of early ocular vasculature and developing neural retina have not been studied in detail and remain unknown. Known roles of early ocular vasculature in developing retina is limited to supply of oxygen and nutrients (Geudens & Gerhardt 2011). Therefore, in order to contribute to our further understanding of the regulatory roles of endothelial cells in developing retina, I present the findings my studies in this dissertation. First, I characterized the retinal phenotype of cloche zebrafish mutants which have extremely reduced endothelial and hematopoietic cells resulting in absence of vasculature and circulation throughout their body (Stainier et al. 1995; Sumanas et al. 2005; Weinstein et al. 1996; Xiong et al. 2008). In cloche mutants, the eyes are microphthalmic and extremely disorganized at 72 hours post fertilization (hpf) Cloche mutants also have defects in differentiation of both neuronal and non-neuronal cells in their retina. My analyses also show that cloche mutants have reduced cell proliferation and increased cell death. Second, in order to identify specific roles of systemic factors versus circulating factors during retinal neurogenesis, I characterized retinal phenotypes of zebrafish embryos after selectively ablating vascular endothelial cells and zebrafish mutants that lack circulation or red blood cells. Absence of endothelial cells affected normal retinal development in zebrafish embryos whereas absence of circulation or circulating red blood cells did not seem to affect retinal neurogenesis. These results suggest that vascular endothelial cells regulate retinal neurogenesis in zebrafish embryos and endothelial cells are required for cell proliferation, cell survival and cell differentiation in developing retina. Identification of regulatory targets from vasculature to control retinal neurogenesis can potentially provide new directions to treat retinal pathologies resulting from abnormal vasculature as well as retinal regeneration in humans.Thesis (Ph.D., Neuroscience) -- University of Idaho, 201