Renal Electrolyte Division, University of Pittsburgh School of Medicine Pittsburgh, PA 15261 USA.
J Cell Sci. 2012 Nov 15;125(Pt 22):5546-54. doi: 10.1242/jcs.111468. Epub 2012 Sep 12.
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.
肾脏功能需要膜蛋白在肾脏管腔的顶侧和基底外侧表面之间进行适当的分布。此外，细胞表面与细胞内隔室之间的蛋白质绝对数量必须与特定的生理需求相适应。Endolyn（CD164）是一种跨膜蛋白，在近端卷曲小管的刷状缘和顶端内体以及肾脏更远端部分的溶酶体中表达。已经表明 Endolyn 调节造血前体细胞和成肌细胞中的 CXCR4 信号；然而，对于成年或发育中的肾脏中的 Endolyn 功能知之甚少。在这里，我们确定 Endolyn 是斑马鱼前肾功能的重要基因。斑马鱼 Endolyn 缺乏哺乳动物蛋白的 N 端粘蛋白样结构域，但在其他方面高度保守。通过原位杂交，我们表明 Endolyn 在斑马鱼大脑、眼睛、肠道和前肾中早期表达。针对 Endolyn 的翻译抑制型 morpholino 寡核苷酸注射的胚胎出现心包水肿、脑积水和身体弯曲。前肾在形态上看起来正常，但注射到共同总静脉的荧光葡聚糖的清除被延迟，这与形态发生胚胎中水平衡调节的缺陷一致。异源表达大鼠 Endolyn 挽救了形态发生胚胎的表型。有趣的是，使用突变大鼠 Endolyn 构建体的挽救实验表明，顶端分拣和内吞/溶酶体靶向基序都需要正常的前肾功能。这表明，Endolyn 的极化靶向和内吞后转运对于该蛋白在哺乳动物肾脏中的正常功能都是必不可少的。
