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Apical targeting and endocytosis of the sialomucin endolyn are essential for establishment of zebrafish pronephric kidney function
Di Mo, Gudrun Ihrke, Simone A. Costa, Lauren Brilli, Anatália Labilloy, Willi Halfter, Chiara Cianciolo Cosentino, Neil A. Hukriede, Ora A. Weisz


Kidney function requires the appropriate distribution of membrane proteins between the apical and basolateral surfaces along the kidney tubule. Further, the absolute amount of a protein at the cell surface versus intracellular compartments must be attuned to specific physiological needs. Endolyn (CD164) is a transmembrane protein that is expressed at the brush border and in apical endosomes of the proximal convoluted tubule and in lysosomes of more distal segments of the kidney. Endolyn has been shown to regulate CXCR4 signaling in hematopoietic precursor cells and myoblasts; however, little is known about endolyn function in the adult or developing kidney. Here we identify endolyn as a gene important for zebrafish pronephric kidney function. Zebrafish endolyn lacks the N-terminal mucin-like domain of the mammalian protein, but is otherwise highly conserved. Using in situ hybridization we show that endolyn is expressed early during development in zebrafish brain, eye, gut and pronephric kidney. Embryos injected with a translation-inhibiting morpholino oligonucleotide targeted against endolyn developed pericardial edema, hydrocephaly and body curvature. The pronephric kidney appeared normal morphologically, but clearance of fluorescent dextran injected into the common cardinal vein was delayed, consistent with a defect in the regulation of water balance in morphant embryos. Heterologous expression of rat endolyn rescued the morphant phenotypes. Interestingly, rescue experiments using mutant rat endolyn constructs revealed that both apical sorting and endocytic/lysosomal targeting motifs are required for normal pronephric kidney function. This suggests that both polarized targeting and postendocytic trafficking of endolyn are essential for the protein's proper function in mammalian kidney.


  • Funding

    This work was supported by the National Institutes of Health [grant number R01-DK54407 to O.A.W.]; a grant-in-aid award from the National Kidney Foundation [NKF/NCA to G.I.]; and the Urinary Tract Epithelial Imaging and Model Organisms Cores of the P30 Pittsburgh Center for Kidney Research [grant number NIH DK079307]. S.A.C. was funded by a Howard Hughes Medical Institute summer scholarship (HHMI 52006971). Deposited in PMC for release after 12 months.

  • Supplementary material available online at

  • Accepted August 6, 2012.
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