Date of Award
Doctor of Philosophy (PhD)
Harald J. Junge
Tin Tin Su
Genetic evidence indicates that specific combinations of accessory proteins and ligands mediate vascular Frizzled (FZD) signaling via beta-catenin in different CNS structures. Accessory proteins in FZD receptor complexes are thought to determine ligand-selectivity and signaling amplitude. In the retina, TSPAN12 is an essential co-activator in Norrin/FZD4 signaling to mediate angiogenesis. The genes encoding mediators of Norrin/FZD4 signaling are linked to familial exudative vitreoretinopathy (FEVR), an inherited retinal disease that can lead to blindness. Yet, the molecular function of TSPAN12 and the specific cell type in which TSPAN12 functions in the retina remains poorly understood. Here, I utilized binding experiments and cell-based assays to demonstrate that TSPAN12 is an essential component of the Norrin receptor complex and physically interacts with FZD4 and Norrin via its extracellular loops, consistent with an action as co-receptor that enhances FZD4 ligand-selectivity for Norrin. I established that FEVR-linked missense mutations in TSPAN12 prevent the incorporation of TSPAN12 into the Norrin receptor complex. In vitro and in Xenopus embryos, TSPAN12 alleviates defects of FZD4 M105V, a mutation that destabilizes the Norrin/FZD4 interaction. Results from mouse conditional genetic studies reveal the requirement for TSPAN12 function in endothelial cells and for endothelial cell/mural cell interactions, artery-vein specifications, and blood-retina barrier maintenance. This study sheds new light on the poorly understood function of accessory proteins as mediators of ligand-specificity in FZD signaling.
Lai, Maria B., "Elucidating the Ligand-Specific Role of Tetraspanin12 as an Essential Co-Activator in Norrin/Frizzled4 Signaling and Retinal Vascularization" (2017). Molecular, Cellular, and Developmental Biology Graduate Theses & Dissertations. 71.