The outer medullary collecting duct (OMCD) plays an important role in bicarbonate reabsorption and acid-base regulation. An apical V-type H+-ATPase and a basolateral [Formula: see text] exchanger, located in intercalated cells of OMCD, mediate the bicarbonate reabsorption. Here we report the identification of a new basolateral [Formula: see text] exchanger in OMCD intercalated cells in rat kidney. Northern hybridizations demonstrated the predominant expression of this transporter, also known as SLC26A7, in the outer medulla, with lower expression levels in the inner medulla. SLC26A7 was recognized as a ∼90-kDa band in the outer medulla by immunoblot analysis and was localized on the basolateral membrane of a subset of OMCD cells by immunocytochemical staining. No labeling was detected in the cortex. Double-immunofluorescence labeling with the aquaporin-2 and SLC26A7 antibodies or anion exchanger-1 and SLC26A7 antibodies identified the SLC26A7-expressing cells as α-intercalated cells. Functional studies in oocytes demonstrated that increasing the osmolality of the media (to simulate the physiological milieu in the medulla) increased the [Formula: see text] exchanger activity mediated via SLC26A7 by about threefold ( P < 0.02 vs. normal condition). We propose that SLC26A7 is a basolateral [Formula: see text] exchanger in intercalated cells of the OMCD and may play an important role in bicarbonate reabsorption in medullary collecting duct.

Albinism, the loss of melanin pigmentation, has evolved in a diverse variety of cave animals but the responsible evolutionary mechanisms are unknown. In Astyanax mexicanus, which has a pigmented surface dwelling form (surface fish) and several albino cave-dwelling forms (cavefish), albinism is caused by loss of function mutations in the oca2 gene, which operates during the first step of the melanin synthesis pathway. In addition to albinism, cavefish have evolved differences in behavior, including feeding and sleep, which are under the control of the catecholamine system. The catecholamine and melanin synthesis pathways diverge after beginning with the same substrate, L-tyrosine. Here we describe a novel relationship between the catecholamine and melanin synthesis pathways in Astyanax. Our results show significant increases in L-tyrosine, dopamine, and norepinephrine in pre-feeding larvae and adult brains of Pachón cavefish relative to surface fish. In addition, norepinephrine is elevated in cavefish adult kidneys, which contain the teleost homologs of catecholamine synthesizing adrenal cells. We further show that the oca2 gene is expressed during surface fish development but is downregulated in cavefish embryos. A key finding is that knockdown of oca2 expression in surface fish embryos delays the development of pigmented melanophores and simultaneously increases L-tyrosine and dopamine. We conclude that a potential evolutionary benefit of albinism in Astyanax cavefish may be to provide surplus L-tyrosine as a precursor for the elevated catecholamine synthesis pathway, which could be important for adaptation to the challenging cave environment.

Predicting organismal phenotypes from genotype data is important for preventive and personalized medicine as well as plant and animal breeding. Although genome-wide association studies (GWAS) for complex traits have discovered a large number of trait- and disease-associated variants, phenotype prediction based on associated variants is usually in low accuracy even for a high-heritability trait because these variants can typically account for a limited fraction of total genetic variance. In comparison with GWAS, the whole-genome prediction (WGP) methods can increase prediction accuracy by making use of a huge number of variants simultaneously. Among various statistical methods for WGP, multiple-trait model and antedependence model show their respective advantages. To take advantage of both strategies within a unified framework, we proposed a novel multivariate antedependence-based method for joint prediction of multiple quantitative traits using a Bayesian algorithm via modeling a linear relationship of effect vector between each pair of adjacent markers. Through both simulation and real-data analyses, our studies demonstrated that the proposed antedependence-based multiple-trait WGP method is more accurate and robust than corresponding traditional counterparts (Bayes A and multi-trait Bayes A) under various scenarios. Our method can be readily extended to deal with missing phenotypes and resequence data with rare variants, offering a feasible way to jointly predict phenotypes for multiple complex traits in human genetic epidemiology as well as plant and livestock breeding.

A variety of natural and synthetic compounds are known to selfassemble to give transmembrane ion channels. 1 Hydrogen-bonded macrocycles that can π-stack are a new type of channel motif. 2 Thus, folate quartets stack to give ion channels in lipid bilayers. 3 This folate assembly had a single-channel conductance of 10-20 picosiemens (pS), values consistent with the quartet's 3 Å diameter. We found that a noncovalent assembly of 16 guanosine monomers could be cross-linked to give a "unimolecular" G-quadruplex that can transport Na + across lipid membranes. 4 We now report that the ditopic guanosine-lithocholate 1 forms discrete channels in phospholipid membranes (Figure 1). These pores are large (nS conductance) and stable, with "open" times of seconds, distinguishing them from most synthetic channels, which typically conduct in the pS range with millisecond lifetimes. 1,5 Lehn and Barboiu have independently shown that ditopic monomers with guanine end groups form supramolecular polymers in cation-templated processes. 6 Possible supramolecular structures built from these ion-templated G 4 -quartets are depicted in Figure 2. In addition to the G 4 -quartet channel, such structures might well stack to form pores for transmembrane transport. Of relevance was Barboiu's demonstration that Na + and K + could be transported across films made from G 4 -quartet polymers. 6b The nucleoside-sterol conjugate 1 has two guanosine groups connected by a bis-lithocholate linker. This spacer was inspired by Kobuke's studies that showed that bis-cholic acid derivatives formed cation-selective channels with pS conductance. 7,8 We envisioned that membrane insertion of 1, followed by formation of G 4 -quartets, might well provide functional pores (Figure 2).Compound 1 was made by coupling 2′,3′-tBDMSi-5′-amino G, 9 with a bis-lithocholic acid. Compound 2, with -NMe amide end groups, was a control. The 1 H NMR spectrum of 1 gave sharp peaks in DMSO-d 6 , a polar solvent that inhibits self-assembly mediated by hydrogen bonding. In contrast, the NMR spectrum of 1 in CDCl 3 gave much broader signals, consistent with self-association in this "poor" solvent.We used CD spectroscopy to gain evidence that 1 forms stacked G 4 -quartets in a nonpolar solvent. 10 Figure 3 shows CD spectra for samples of 1 in CHCl 3 . The CD spectrum of 1 (blue) was taken after isolation from a silica gel. This sample showed a weak Cotton band in the 200-280 nm region, suggesting some stacked G 4 -quartets. 10 We added [2.2.2]-cryptand to ensure that any adventitious cations bound by 1 were sequestered. Indeed, the resulting spectrum (green trace) was inactive. We next stirred the mixture of 1 and [2.2.2]-cryptand in the presence of excess K + 2,6-dinitrophenolate (DNP). The CD spectrum of ditopic 1 was much different after extraction of K + DNP -(red trace). This sample showed a CD signature diagnostic for stacked G-quartets, with a positive band at λ ) 266 nm and a negative peak at λ ) 240 nm. 10 The complex formed by 1 and K + also showed a strong Cotton ba...

Pendrin is an apical Cl(-)/OH(-)/HCO(3)(-) exchanger in beta-intercalated cells (beta-ICs) of rat and mouse cortical collecting duct (CCD). However, little is known about its regulation in acid-base disorders. Here, we examined the regulation of pendrin in metabolic acidosis, a condition known to decrease HCO(3)(-) secretion in CCD. Rats were subjected to NH(4)Cl loading for 4 days, which resulted in metabolic acidosis. Apical Cl(-)/HCO(3)(-) exchanger activity in beta-ICs was determined as amplitude and rate of intracellular pH change when Cl was removed in isolated, microperfused CCDs. Intracellular pH was measured by single-cell digital ratiometric imaging using fluorescent pH-sensitive dye 2',7'-bis-(3-carboxypropyl)-5-(and-6)-carboxyfluorescein-AM. Pendrin mRNA expression in kidney cortex was examined by Northern blot hybridizations. Expression of pendrin protein was assessed by indirect immunofluorescence. Microperfused CCDs isolated from acidotic rats demonstrated approximately 60% reduction in apical Cl(-)/HCO(3)(-) exchanger activity in beta-ICs (P < 0.001 vs. control). Northern blot hybridizations indicated that the mRNA expression of pendrin in kidney cortex decreased by 68% in acidotic animals (P < 0.02 vs. control). Immunofluorescence labeling demonstrated significant reduction in pendrin expression in CCDs of acidotic rats. We conclude that metabolic acidosis decreases the activity of the apical Cl(-)/HCO(3)(-) exchanger in beta-ICs of the rat CCD by reducing the expression of pendrin. Adaptive downregulation of pendrin in metabolic acidosis indicates the important role of this exchanger in acid-base regulation in the CCD.