Date of Award


Degree Type


Degree Name

Master of Science


Physiology and Pharmacology


Dr. Arthur Brown

Second Advisor

Lesley Stephen

Third Advisor

Mike Bygrave


The formation of the endocardial cushions is a critical event during heart development and gives rise to the valvuloseptal structures of the heart. A key step in the formation of the endocardial cushions is the endothelial to mesenchymal transition (EMT) that occurs in the atrioventricular canal and outflow tracts. Previous work has shown that EphA3 and one of its ligands, ephrin-Al, are expressed in complementary patterns in the developing endocardial cushions and that the majority of EphA3= mice die within the first 48 hours ofbirth from improper formation of the valvuloseptal structures. Analysis of endocardial cushion explants from E10.5 embryos demonstrated that fewer EphA3~^ cells completed the EMT required for normal morphogenesis compared to the wildtype (WT) explants. These initial studies demonstrated the importance of EphA3 to endocardial cushion development but did not prove that the EMT defect was due to a loss of ephrin-Al-EphA3 signaling nor did these studies determine where along the EMT differentiation program EphA3 functions or whether surviving adult EphA37 mice have proper functioning valves. Using biochemical gain of function and loss of function studies in endocardial cushion explants we demonstrate that the EMT defect in EphAS^ endocardial cushions is due to a loss of ephrin-Al-EphA3 signaling. Gene expression analysis and the explant studies suggest an independent or late role for ephrin-Al-EphA3 signaling in the known EMT pathway. Finally micro-ultrasound analysis shows that the EphA37 adult mice appear to have proper functioning valves.



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