New Mechanisms of Heterotaxy and Congenital Heart Disease: Nucleoporins at Cilia

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Project Summary Congenital heart disease (CHD) is one of the major causes of infant mortality and morbidity in the US. However, we know little about the genetic causes of this disease. Multiple studies have now identified nucleoporins, the protein components that build nuclear pore complexes, as candidate genes for Heterotaxy, a disorder of left-right patterning that can lead to a severe form of CHD. In our previous work, we proposed a likely model for how nucleoporins could contribute to left-right patterning by establishing that Nup188 and its binding partner Nup93 are essential for cardiac development, left-right patterning and cilia in a frog model. Importantly, we discovered that both Nup188 and Nup93 are localized to the bases of cilia where they form assemblies that are structurally distinct from nuclear pore complexes. Despite this progress, we do not yet have a clear catalogue of the nucleoporins that localize to cilia bases, nor do we understand precisely how they function. To meet these challenges, we intend to fully leverage the unique and complementary expertise of our team that includes clinician scientists, developmental and cell biologists, including super-resolution microscopists. We will thus take a multidisciplinary approach to: 1) Interrogate the function of emerging nucleoporin variants linked to CHD in our rapid and efficient Xenopus CHD model; 2) Use proximity-detection methods like BioID in cell culture to fully identify the nucleoporins that localize to cilium bases and their cilium- specific binding partners; and 3) Use these data in concert with sophisticated pulse-chase analyses coupled to next generation multi-color 3D super resolution imaging to fully define the mechanisms of nucleoporin recruitment and their nanoscale distribution at the cilium base. Lastly, we will directly explore nucleoporin function in building both primary and multi-cilia in cell culture and Xenopus models. Our results promise to provide a framework to identify how emerging nucleoporin (and cilium base) gene variants underlie CHD while also informing fundamental mechanisms that function at the cell and tissue-level.