The SLC26 gene family encodes anion transporters with diverse functional attributes: (a) anion exchanger, (b) anion sensor and (c) anion conductance (likely channel). We have cloned and studied Slc26a9, a paralog expressed mostly in lung and stomach. Immunohistochemistry shows that Slc26a9 is present at apical and intracellular membranes of lung and stomach epithelia. Using expression in Xenopus laevis oocytes and ion-sensitive microelectrodes, we discovered that Slc26a9 has a novel function not found in any other Slc26 proteins -cation coupling. Intracellular pH and voltage measurements show that Slc26a9 is a nCl --HCO 3 -exchanger, suggesting roles in gastric HCl secretion or pulmonary HCO 3 -secretion; Na + electrodes and uptakes reveal that Slc26a9 has a cationdependence. Single channel measurements indicate that Slc26a9 displays discrete open and close states. These experiments show that Slc26a9 has three discrete physiological modes: nCl --HCO 3 -exchanger, Cl -channel, and Na + -anion cotransporter. Thus, the Slc26a9 transporter-channel is uniquely suited for dynamic and tissue-specific physiology or regulation in epithelial tissues.

Autosomal Dominant Polycystic Kidney Disease (ADPKD) is the most common monogenic kidney disease and the fourth leading cause of end-stage renal disease, responsible for 5–10% of cases. The disease is characterized by relentless development and growth of cysts causing progressive kidney enlargement associated with hypertension, pain, reduced quality of life, and eventually kidney failure. It is caused by mutations to PKD1 or PKD2, encoding polycystin-1 and polycystin-2, respectively. Their function and the molecular mechanisms responsible for the development of polycystic kidney disease are not well understood. The objective of this review is to synthesize a large body of literature that examines how reduction of functional PC1 or PC2 at the primary cilia and/or the endoplasmic reticulum directly disrupts intracellular calcium signaling and indirectly disrupts calcium regulated cAMP and purinergic signaling. We propose a hypothetical model where dysregulated metabolism of cAMP and purinergic signaling increase the sensitivity of principal cells in collecting ducts and of tubular epithelial cells in the distal nephron to the constant tonic action of vasopressin. The resulting magnified response to vasopressin further enhances the disruption of calcium signaling initiated by mutations to PC1 or PC2 and activates downstream signaling pathways responsible for impaired tubulogenesis, cell proliferation, increased fluid secretion and interstitial inflammation.

Renal agenesis (RA) is one of the more extreme examples of congenital anomalies of the kidney and urinary tract (CAKUT). Bilateral renal agenesis is almost invariably fatal at birth, and unilateral renal agenesis can lead to future health issues including end-stage renal disease. Genetic investigations have identified several gene variants that cause RA, including ,, and However, whereas compound null mutations of genes encoding α and γ retinoic acid receptors (RARs) cause RA in mice, to date there have been no reports of variants in RAR genes causing RA in humans. In this study, we carried out whole exome sequence analysis of two families showing inheritance of an RA phenotype, and in both identified a single candidate gene, Analysis of a zebrafish loss-of-function mutant revealed defects in the pronephric kidney just prior to death, and F0 CRISPR/Cas9 mutagenesis of in the mouse revealed kidney agenesis phenotypes, implicating in this disorder. GREB1L resides in a chromatin complex with RAR members, and our data implicate GREB1L as a coactivator for RARs. This study is the first to associate a component of the RAR pathway with renal agenesis in humans.

Neuregulin is required for proper oligodendrocyte development, but which receptors are involved and whether neuregulin promotes or inhibits maturation remain controversial. To assess the roles of the neuregulin receptor ErbB4 in oligodendrocyte development, we examined oligodendrocyte initiation and maturation in cultures derived from erbB4 knock-out mice and rat spinal cord in the presence of neutralizing erbB4 antibodies. No differences in the development of O4 ϩ oligodendrocytes were detected in the presence or absence of erbB4 signaling. All four epidermal growth factor receptor family members were detected in the ventral neural tube at approximately the time of initial oligodendrocyte development, consistent with redundancy in neuregulin receptor signaling at the onset of oligodendrocyte development. In contrast, greater numbers of differentiated (monoclonal antibody O1 ϩ ) oligodendrocytes developed in neural tube explants from erbB4 ؊/؊ mice than either erbB4 ؉/؉ or erbB4 ؉/؊ littermates as well as in cultures treated with anti-erbB4. These data indicate that ErbB4 is not required for oligodendrocyte development and, in fact, inhibits oligodendrocyte lineage maturation. Together with previous studies, these data suggest a model in which early oligodendrocyte lineage development is regulated by promiscuous neuregulin receptor signaling, but subsequent lineage progression occurs through a balance of receptor-specific promotion or inhibition of maturation.

Meckel syndrome (MKS) is a lethal disorder associated with renal cystic disease, encephalocele, ductal plate malformation and polydactyly. MKS is genetically heterogeneous and part of a growing list of syndromes called ciliopathies, disorders resulting from defective cilia. TMEM67 mutation (MKS3) is a major cause of MKS and the related ciliopathy Joubert syndrome, although the complete etiology of the disease is not well understood. To further investigate MKS3, we analyzed phenotypes in the Tmem67 null mouse (bpck) and in zebrafish tmem67 morphants. Phenotypes similar to those in human MKS and other ciliopathy models were observed, with additional eye, skeletal and inner ear abnormalities characterized in the bpck mouse. The observed disorganized stereociliary bundles in the bpck inner ear and the convergent extension defects in zebrafish morphants are similar to those found in planar cell polarity (PCP) mutants, a pathway suggested to be defective in ciliopathies. However, analysis of classical vertebrate PCP readouts in the bpck mouse and ciliary organization analysis in tmem67 morphants did not support a global loss of planar polarity. Canonical Wnt signaling was upregulated in cyst linings and isolated fibroblasts from the bpck mouse, but was unchanged in the retina and cochlea tissue, suggesting that increased Wnt signaling may only be linked to MKS3 phenotypes associated with elevated proliferation. Together, these data suggest that defective cilia loading, but not a global loss of ciliogenesis, basal body docking or PCP signaling leads to dysfunctional cilia in MKS3 tissues.

Abstract. SLC26 anion exchangers transport monovalent and divalent anions, with a diversity of anion specifi city and stoichiometry. Our

Vitamin D and vitamin D metabolites such as 25(OH) 2 D 3 ] circulate in the serum of fish. The receptor for 1␣,25(OH) 2 D 3 (VDR) has previously been cloned from fish intestine, and ligand binding assays have shown the presence of the VDR in the gills, intestine, and liver of fish. Using immunohistochemical methods with specific antibodies against the VDR, we now report that the VDR is widely expressed in tissues of the adult male and female zebrafish, Danio rerio, specifically in epithelial cells of gills, tubular cells of the kidney, and absorptive cells in the intestine. Additionally, the VDR is expressed in the skin, the olfactory organ, the retina, brain, and spinal cord. Sertoli cells of the testis, oocytes, acinar cells of the pancreas, hepatocytes, and bile duct epithelial cells express substantial amounts of the receptor. Osteoblast-like cells and chondrocytes also express VDR. Preimmune serum and antiserum preadsorbed with Danio VDR protein fails to detect VDR in the same tissues. The VDR is also present in the developing eye, brain, and otic vesicle of 48-and 96-h postfertilization zebrafish embryos. Parenteral administration of 1␣,25(OH) 2 D 3 increases concentrations of VDR in intestinal epithelial cells but not in epithelial cells of the gills. Lithocholic acid, however, does not alter concentrations of VDR after parenteral administration. The data suggest that VDR is widely distributed in tissues of the zebrafish, D. rerio, and is likely to play important roles in epithelial transport, bone, and endocrine function. Furthermore, concentrations of the receptor seem to be regulated by its ligand, 1␣,25-dihydroxyvitamin D but not by lithocholic acid. Zebrafish may serve as a useful model in which to assess the function of the VDR in diverse tissues.

The expanding field of precision gene editing is empowering researchers to directly modify DNA. Gene editing is made possible using synonymous technologies: a DNA-binding platform to molecularly locate user-selected genomic sequences and an associated biochemical activity that serves as a functional editor. The advent of accessible DNA-targeting molecular systems, such as zinc-finger nucleases, transcription activator-like effectors (TALEs) and CRISPR-Cas9 gene editing systems, has unlocked the ability to target nearly any DNA sequence with nucleotide-level precision. Progress has also been made in harnessing endogenous DNA repair machineries, such as non-homologous end joining, homology-directed repair and microhomology-mediated end joining, to functionally manipulate genetic sequences. As understanding of how DNA damage results in deletions, insertions and modifications increases, the genome becomes more predictably mutable. DNA-binding platforms such as TALEs and CRISPR can also be used to make locus-specific epigenetic changes and to transcriptionally enhance or suppress genes. Although many challenges remain, the application of precision gene editing technology in the field of nephrology has enabled the generation of new animal models of disease as well as advances in the development of novel therapeutic approaches such as gene therapy and xenotransplantation.