Investigation of the role of Unc45a in aortic arch development
Anderson, Matthew J.
Thesis (Ph.D.)--Georgetown University, 2008.; Includes bibliographical references. Human congenital cardiovascular malformations are the most frequently observed birth defects with a large number stemming from malformation of the aortic arches. The etiologies of many of these malformations are unknown. The zebrafish kurzschluss mutant offers a model to study aortic arch malformation, as a mutation within the gene encoding Unc45a, a putative chaperone implicated in ovarian cancer, creates an arteriovenous malformation (AVM) between the posterior aortic arches 5 and 6 and a primitive head vein. This AVM shunts blood directly back to the heart, confining almost all blood to a small anterior circulation loop. In this work we sought to describe the mechanism of aortic arch formation in wild type zebrafish embryos; identify factors that contribute to AVM development in kurzschluss mutants; confirm the role of unc45a mutation in the kurzschluss phenotype; and determine the cell autonomy of the kurzschluss/unc45a mutation. To clarify the mechanism of aortic arch formation, we documented the development of these vessels in a dynamic manner in live zebrafish embryos, revealing for the first time a combined vasculogenic and angiogenic origin of the aortic arches. In comparing aortic arch development in kurzschluss embryos to wild type embryos, we found that general patterning is normal, but lumenization of aortic arches 5 and 6 is delayed, and connections of these vessels to the ventral and dorsal aortae are abnormal. These defects generate transiently blind-ended aortic arches that fill with blood, distend, and contact and fuse with and adjacent vein. Additional defects were noted in ventral aorta and branchial cartilage patterning in the fifth and sixth pharyngeal arches. Rescue and phenocopy experiments confirmed the role of unc45a in kurzschluss vessel and cartilage phenotypes, and reconstitution of unc45a expression specifically within the endothelium suggested that unc45a is required within aortic arch endothelium to prevent AVM formation. In summary, this work is the first to provide a detailed description of the formation of the aortic arches in any vertebrate system, and the first to implicate unc45a in vascular development. This knowledge will hopefully lead to a better understanding of the mechanisms leading to congenital aortic arch malformations and arteriovenous shunts.
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