Abstract
Mammals achieve the highest urine concentrations of any vertebrate, a feat that hinges on generating steep osmotic gradients within the renal medulla. Interestingly, the region with the highest osmolality, the inner medulla, is unique to mammals. Among the nephron’s segments, the ascending thin limb (aTL) is the sole element exclusive to this zone and is thought to mediate passive salt reabsorption. However, the architecture and functional impact of the aTL have remained obscure. Here we uncover an unexpected morphogenetic program in the aTL, characterized by extensive apical-junctional interdigitations that greatly increase cell-to-cell contact area. Integrating single-nucleus transcriptomics with high-resolution imaging, we identify claudin-10b, a tight junction protein and paracellular cation pore, as a central driver of this architecture. Inducible deletion of claudin-10b specifically in the aTL abolishes membrane interdigitations and markedly reduces urine-concentrating ability, thereby establishing a direct link between segment-specific epithelial morphology and whole-organ function. Claudin-10b proves necessary for interdigitation formation, acting through transcellular adhesion and interaction with the tight-junction scaffold ZO1. These findings offer definitive evidence that the inner medulla and aTL are essential for maximal urinary concentration, while revealing a non-canonical, morphogenetic role for claudin-10b.
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Data availability
The single nucleus RNA sequencing data generated in this study have been deposited in the Gene Expression Omnibus database under accession code GSE295103. The processed mean expression data and differential gene expression analysis are available in Supplementary Data 1–7. All other data supporting this study is available from the corresponding author upon request. Source data are provided with this paper.
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Acknowledgements
We thank the UTSW O’Brien Kidney Research Core, CRI Transgenic Core, McDermott Sequencing Core, and Mineral Metabolism Core. We thank Elizabeth Chen, D.J. Pan, Josh Mendell, and Don Hilgemann (UTSW) for helpful suggestions. We thank Mikio Furuse (National Institute for Physiological Sciences) and Tetsu Otani (Tokyo Metropolitan University) for cell lines and suggestions. This work was funded by NIH R01DK118032 (D.K.M.), R01DK141873 (D.K.M.), RM1GM145399 (K.M.D.) and R35GM133522 (R.F.).
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J.N.W., M.T.D., T.J.C., and D.K.M. conceptualized the study and designed experiments. J.N.W., S.O., B.L.F., J.B.P., C.H., K.G., H.L., A.M.R., and J.M.W. conducted experiments. J.N.W., B.L.F., J.B.P., K.G., and A.M.R. executed mouse studies. J.N.W. and S.O. generated and analyzed cell lines. J.N.W. conducted immunofluorescence and confocal imaging. J.N.W., S.O., C.H., R.W., S.Z., and D.K.M. analyzed data. C.P.C. executed the single nucleus RNA sequencing bioinformatic analysis. B.L.F., H.L., K.M.D., and R.P.F. collected light sheet microscopy images. J.N.W. and D.K.M. wrote the manuscript. All authors reviewed and revised the manuscript.
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K.M.D. and R.P.F. hold a patent for the axially scanned light-sheet microscope that is currently licensed by Intelligent Imaging Innovations, Inc. and subsequently sub-licensed by Life Canvas Technologies, but do not have any investment interests or financial stakes in these companies. K.M.D. has an investment interest in Discovery Imaging Systems, LLC. All other authors have no competing interests.
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Warshaw, J.N., Oh, S., Chaney, C.P. et al. An epithelial morphogenetic program for maximal urine concentration. Nat Commun (2026). https://doi.org/10.1038/s41467-026-70938-7
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DOI: https://doi.org/10.1038/s41467-026-70938-7
