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Permanent link (DOI): https://doi.org/10.7939/R32F7K033

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The Role of Forkhead Box Transcription Factors in Zebrafish Ocular Development and the Superior Ocular Fissure Open Access

Descriptions

Other title
Subject/Keyword
inferior ocular fissure
apoptosis
gdf6a
Forkhead Box
proliferation
cyp1b1
Microphthalmia, anophthalmia, coloboma
ocular
zebrafish
retinoic acid
superior ocular fissure
eye development
Type of item
Thesis
Degree grantor
University of Alberta
Author or creator
Stach, Tara R
Supervisor and department
Ordan Lehmann (Medical Genetics, Ophthalmology)
Examining committee member and department
Andrew Waskiewicz (Biological Sciences)
Roseline Godbout (Oncology)
David Eisenstat (Medical Genetics, Pediatrics)
Department
Medical Sciences-Medical Genetics
Specialization

Date accepted
2014-09-23T16:22:03Z
Graduation date
2014-11
Degree
Master of Science
Degree level
Master's
Abstract
Ocular development is a tightly orchestrated process that is dependent upon precise environmental and genetic factors. Disruption of this can result in microphthalmia, anophthalmia and coloboma (MAC), which is a spectrum of congenital ocular disease with lifelong consequences affecting sight. In particular, coding anomalies in a member of the Bone Morphogenetic Protein family, GDF6, results in MAC in patients. Using zebrafish gdf6a-/- mutants, we have found that the microphthalmia present in both patients and model organisms appears to be due the requirement for Gdf6a in the regulation of ocular proliferation, progenitor cell survival, and apoptosis in the developing eye. Additionally, we have found that Gdf6a is located upstream of two forkhead box (FOX) transcription factor genes, foxi1 and foxi2, which provide dorsal-ventral polarity to a region where ocular progenitor cells reside, the ciliary marginal zone (CMZ). This is the first report of its kind regarding spatio-temporal identity of the CMZ, and we show that foxi2 and gdf6a lie on converging genetic pathways that regulate ocular size. The forkhead box (FOX) proteins are a family of transcription factors with diverse roles in development such as patterning of neural tissue, cell migration, proliferation, differentiation and survival. Mutations in FOX genes are associated with blinding ocular disorders that occur due to malformation of anterior segment components, and the failure of the optic nerve to correctly innervate the brain. Based on expression patterns and a regulation by Gdf6a, we hypothesized that foxi1 and foxi2 have roles in the patterning and growth of the retina. Knockdown of either foxi1 or foxi2 expression using morpholino (MO) technology resulted in aberrant dorsal-ventral ocular patterning and MAC phenotypes. However, foxi1-/- embryos do not have ocular phenotypes similar to those of the morphant, suggesting compensation by redundant genes, an allele that is not fully disruptive to protein function, or off-target MO effects. The choroid fissure is a well-recognized developmental structure whose failure to close results in coloboma affecting structures of the inferior eye. However, patients with coloboma affecting structures of the superior eye led us to discover the superior ocular fissure, present during zebrafish ocular development and indicative of ~450 million years of evolutionary conservation. Biochemical modeling of transheterozygous CYP1B1 coding anomalies in a proband indicated these might underlie the pathogenicity of superior coloboma, with a requirement for this enzyme to metabolize vitamin A to its active derivative, retinoic acid (RA). Examination of the developing zebrafish retina shows expression of cyp1b1 and other RA metabolism enzymes at the locations of the ocular fissures, and supplementation of vitamin A to a coloboma model during development rescued the phenotype by facilitating closure of the inferior ocular fissure. Finally, I find that antagonism between the FOX genes foxg1 and foxd1 determine the location of fissure formation, with knockdown resulting in superior fissure shift to the nasal axis, or duplication, respectively.
Language
English
DOI
doi:10.7939/R32F7K033
Rights
Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
Citation for previous publication
French CR, Stach TR, March LD, Lehmann OJ, Waskiewicz AJ. Apoptotic and Proliferative Defects Characterize Ocular Development in a Microphthalmic BMP Model. Invest Ophthalmol Vis Sci. 2013 Jul 10;54(7):4636-47

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