Nuclear action of a novel fish kisspeptin receptor isoform

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The project addresses the interesting topic of proteins that take on additional roles after a gene duplication event. It focuses on the kisspeptin hormone and its receptor, a hormonal signaling pathway that plays key roles in the control of reproduction. The kisspeptin receptor is a member of the G-protein coupled receptor (GPCR) family, the largest protein family. The textbook view of GPCR signaling is that hormone binding at the cell surface causes a conformational change in the transmembrane receptor protein and promotes its interaction with G proteins to alter the activity of enzymes and ion channels inside the cell or in the cell membrane, leading to specific cellular responses. There is increasing evidence that this view may be too simplistic, because a number of GPCRs have been found to be located not only on the cell membrane but also in various compartments within cells. The researchers have discovered that the zebrafish kisspeptin receptor b gene encodes several proteins, one of which is located in the nucleus and has nuclear activity. These findings present the exciting possibility of a previously unrecognized nuclear function of a GPCR. This project is designed to test this hypothesis. The results will provide new insights into the understanding of how the kisspeptin pathway regulates fish reproduction, and should lead to applications in the aquaculture industry. This project will provide training opportunities for a diverse group of students at all levels, and will benefit society by engaging K-12 students and the general public in educational outreach activities.The kisspeptin ligand (KISS1) and receptor (KISS1R) hormonal pathway plays key roles in the neuroendocrine control of reproduction in mammals. The mammalian KISS1-KISSR pathway also has non-reproductive functions with poorly understood mechanisms. Recent studies suggest that the zebrafish has two kisspeptin receptor genes. While the zebrafish kiss1ra gene encodes a single G-protein coupled receptor (GPCR) expressed in the brain, the kiss1rb gene encodes a full-length GPCR as well as four alternatively spliced isoforms. These truncated isoforms, termed kiss1rb-derived proteins (KRBDPs), are expressed in the brain and in many peripheral tissues. Functional analysis results suggest that these KRBDP transcripts can be translated into protein products, but none are located on the plasma membrane. Intriguingly, KRBDP3 is detected in the nucleus and possesses ligand-independent transactivation activity when tested in vitro. This project will test the hypothesis that KRBDP3 is localized in the nucleus and regulates gene expression in the brain and/or peripheral tissues. The results will elucidate the functions of a novel GPCR isoform in the nucleus and identify its target genes. This project will also uncover the in vivo functions of the duplicated Kiss1-Kiss1r pathway in the brain and peripheral tissues in a fish model. This project contains technical innovations that will make it possible to dissect the functions of different alternatively spliced gene products and to visualize their expression and subcellular localization in vivo. It will provide high-quality research training for a diverse group of students at all levels, and public educational activities in partnership with the University of Michigan Museum of Natural History.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.