Abstract

Osmoregulation is essential for organisms to adapt to the exterior environment and plays an important role in embryonic organogenesis. Tubular organ formation usually involves a hyperosmotic lumen environment. The mechanisms of how the cells respond and regulate lumen formation remain largely unknown. Here, we reported that the nuclear factor of activated T cells-5 (NFAT5), the only transcription factor in theNFATfamily involved in the cellular responses to hypertonic stress, regulated notochord lumen formation in chordateCiona.Ciona NFAT5(Ci-NFAT5) was expressed in notochord, and its expression level increased during notochord lumen formation and expansion. Knockout and expression of the dominant negative ofNFAT5inCionaembryos resulted in the failure of notochord lumen expansion. We further demonstrated that theCi-NFAT5 transferred from the cytoplasm into nuclei in HeLa cells under the hyperosmotic medium, indicatingCi-NFAT5can respond the hypertonicity. To reveal the underly mechanisms, we predicted potential downstream genes ofCi-NFAT5and further validatedCi-NFAT5-interacted genes by the luciferase assay. The results showed thatCi-NFAT5 promotedSLC26A6expression. Furthermore, expression of a transport inactivity mutant ofSLC26A6(L421P) in notochord led to the failure of lumen expansion, phenocopying that ofCi-NFAT5knockout. These results suggest thatCi-NFAT5regulates notochord lumen expansion via the SLC26A6 axis. Taken together, our results reveal that the chordateNFAT5responds to hypertonic stress and regulates lumen osmotic pressure via an ion channel pathway on luminal organ formation.Keywords:NFAT5;notochord;lumen formation;osmotic stress;ascidian