The Role of the Adaptor Protein Enkurin in Left-Right Patterning- a Promising Link Between Polycystin-2 and Calcium Signaling - Project Summary Defects in left-right (LR) patterning underlie some of the most severe congenital heart defects (CHDs), which can be fatal if not surgically corrected. However, we still do not have a complete understanding of the genes and cell signaling pathways that are used to pattern the LR body axis, which severely limits our ability to identify genetic risk factors for CHDs. In fish, frogs, mice, and humans, LR patterning is initiated within ciliated structures known as left-right organizers (LROs). Motile cilia within these LROs rotate and generate a leftward fluid flow that is proposed to be mechanically sensed by a cation channel complex in the cilium composed of Polycsytin-2 (Pkd2) and Polycystin 1-Like-1 (Pkd1L1). In response to flow, this channel complex would generate a calcium gradient on the left side of KV. The resulting signaling pathway ultimately culminates in the downregulation of the Transforming Growth Factor Beta (TGF-β) inhibitor dand5 mRNA on the left side of Kupffer’s Vesicle (KV)- the zebrafish LRO. However, the downstream effectors of fluid flow that link the channel and calcium signaling to the downregulating of dand5, are unknown. My preliminary work identified Enkurin as highly expressed in KV. Past published work on Enkurin has shown that Enkurin binds to Transient receptor potential channel (TRPC) cation channels to physically link them calcium signaling effectors in mouse sperm. As Pkd2 is in the same TRP family with these TRPC channels, I hypothesize Enkurin binds Pkd2 and links it to downstream calcium signaling machinery in KV, which is required to regulate dand5 mRNA. To test this hypothesis, I will characterize an enkurin mutant to determine how LR patterning and Calmodulin signaling is affected in KV (aim 1). I will determine where Enkurin localizes subcellularly, assess for changes in subcellular localization in response to fluid flow, and test for colocalization with Pkd2 and Calmodulin (aim 2). I will explore the Enkurin interactome directly testing the binding of Enkurin to Pkd2 and Calmodulin. I will also use TurboID as an unbiased approach to characterize Enkurin’s interactome and identify additional binding partners (aim 3). This project will fill a significant knowledge gap in identifying the proteins and processes downstream of cilia that regulate LR patterning. Importantly, this work has the potential to directly link Pkd2 to downstream calcium signaling for the first time. This project will also identify new binding partners of Enkurin, which could be playing key roles in LR patterning, and thus identify previously unappreciated risk factors for CHDs. This project will also advance my skills in protein biochemistry, developmental biology, and imaging techniques, and the supportive and collaborative nature of Princeton’s Department of Molecular Biology and the Burdine lab will further support my scientific development.
