Biomedical subjects

Jinhua Zhao

Publications and source records attributed to Jinhua Zhao.

7 recordsLinked to original sources

PubMed2006

Polycystin-2 immunolocalization and function in zebrafish.

Polycystin-2 functions as a cation-permeable transient receptor potential ion channel in kidney epithelial cells and when mutated results in human autosomal dominant polycystic kidney disease. For further exploration of the in vivo functions of Polycystin-2, this study examined its expression and function during zebrafish embryogenesis. pkd2 mRNA is ubiquitously expressed, and its presence in the larval kidney could be confirmed by reverse transcription-PCR on isolated pronephroi. Immunostaining with anti-zebrafish Polycystin-2 antibody revealed protein expression in motile kidney epithelial cell cilia and intracellular cell membranes. Intracellular localization was segment specific; in the proximal nephron segment, Polycystin-2 was localized to basolateral cell membranes, whereas in the caudal pronephric segment, Polycystin-2 was concentrated in subapical cytoplasmic vesicles. Polycystin-2 also was expressed in muscle cells and in a variety of sensory cells that are associated with mechanotransduction, including cells of the ear, the lateral line organ, and the olfactory placodes. Disruption of Polycystin-2 mRNA expression resulted in pronephric kidney cysts, body axis curvature, organ laterality defects, and hydrocephalus-defects that could be rescued by expression of a human PKD2 mRNA. In-frame deletions in the first extracellular loop and C-terminal phosphofurin acidic cluster sorting protein-1 (PACS-1) binding sites in the cytoplasmic tail caused Polycystin-2 mislocalization to the apical cell surface. Unlike zebrafish intraflagellar transport protein (IFT) mutants, cyst formation was not associated with cilia defects and instead correlated with reduced kidney fluid output, expansion of caudal duct apical cell membranes, and occlusion of the caudal pronephric nephron segment.

Amino Acid Sequence↗

PubMed2005

Zebrafish slc4a2/ae2 anion exchanger: cDNA cloning, mapping, functional characterization, and localization.

Although the zebrafish has been used increasingly for the study of pronephric kidney development, studies of renal ion transporters and channels of the zebrafish remain few. We report the cDNA cloning and characterization of the AE2 anion exchanger ortholog from zebrafish kidney, slc4a2/ae2. The ae2 gene in linkage group 2 encodes a polypeptide of 1,228 aa exhibiting 64% aa identity with mouse AE2a. The exon-intron boundaries of the zebrafish ae2 gene are nearly identical to those of the rodent and human genes. Whole-mount in situ hybridization detects ae2 mRNA in prospective midbrain as early as the five-somite stage, then later in the pronephric primordia and the forming pronephric duct, where it persists through 72 h postfertilization (hpf). Zebrafish Ae2 expressed in Xenopus laevis oocytes mediates Na(+)-independent, electroneutral (36)Cl(-)/Cl(-) exchange moderately sensitive to inhibition by DIDS, is inhibited by acidic intracellular pH and by acidic extracellular pH, but activated by (acidifying) ammonium and by hypertonicity. Zebrafish Ae2 also mediates Cl(-)/HCO(3)(-) exchange in X. laevis oocytes and accumulates in or near the plasma membrane in transfected HEK-293 cells. In 24-48 hpf zebrafish embryos, the predominant but not exclusive localization of Ae2 polypeptide is the apical membrane of pronephric duct epithelial cells. Thus Ae2 resembles its mammalian orthologs in function, mechanism, and acute regulation but differs in its preferentially apical expression in kidney. These results will inform tests of the role of Ae2 in zebrafish kidney development and function.

Amino Acid Sequence↗

PubMed2005

roundabout4 is essential for angiogenesis in vivo.

Stereotypical patterns of vascular and neuronal networks suggest that specific genetic programs tightly control path determination and, consequently, angiogenesis and axon-guidance mechanisms. Our study focuses on one member of the roundabout family of receptors, which traditionally mediate repulsion from the midline. Here, we characterize a fourth member of this family, roundabout4 (robo4), which is the predominant roundabout (robo) that is expressed in embryonic zebrafish vasculature. Gene knockdown and overexpression approaches show that robo4 is essential for coordinated symmetric and directed sprouting of intersomitic vessels and provide mechanistic insights into this process. Also, human robo4 gene functionally compensates for loss of robo4 gene function, suggesting evolutionary conservation. This article reports an endothelial-specific function for a robo gene in vertebrates in vivo.

Animals↗

PubMed2005

Evidence from renal proximal tubules that HCO3- and solute reabsorption are acutely regulated not by pH but by basolateral HCO3- and CO2.

Respiratory acidosis, a decrease in blood pH caused by a rise in [CO(2)], rapidly triggers a compensatory response in which the kidney markedly increases its secretion of H(+) from blood to urine. However, in this and other acid-base disturbances, the equilibrium CO(2) + H(2)O HCO(3)(-) + H(+) makes it impossible to determine whether the critical parameter is [CO(2)], [HCO(3)(-)], and/or pH. Here, we used out-of-equilibrium CO(2)/HCO(3)(-) solutions to alter basolateral (BL) [HCO(3)(-)], [CO(2)], or pH, systematically and one at a time, on isolated perfused S2 rabbit proximal tubules. We found that increasing [HCO(3)(-)](BL) from 0 to 44 mM, at a fixed [CO(2)](BL) of 5% and a fixed pH(BL) of 7.40, caused HCO(3)(-) reabsorption (J(HCO(3))) to fall by half but did not significantly affect volume reabsorption (J(V)). Increasing [CO(2)](BL) from 0% to 20%, at a fixed [HCO(3)(-)](BL) of 22 mM and pH(BL) of 7.40, caused J(HCO(3)) to rise 2.5-fold but did not significantly affect J(V). Finally, increasing pH(BL) from 6.80 to 8.00, at a fixed [HCO(3)(-)](BL) of 22 mM and [CO(2)](BL) of 5%, did not affect either J(HCO(3)) or J(V). Analysis of the J(HCO(3)) and J(V) data implies that, as the tubule alters J(HCO(3)), it compensates the reabsorption of other solutes to keep J(V) approximately constant. Because the cells cannot respond acutely to pH changes, we propose that the responses of J(HCO(3)) and the reabsorption of other solutes to changes in [HCO(3)(-)](BL) or [CO(2)](BL) involve sensors for basolateral HCO(3)(-) and CO(2).

Absorption↗

PubMed2004

Effect of extracellular acid-base disturbances on the intracellular pH of neurones cultured from rat medullary raphe or hippocampus.

Previous reports suggest that an important characteristic of chemosensitive neurones is an unusually large change of steady-state intracellular pH in response to a change in extracellular pH (DeltapH(i)/DeltapH(o)). To determine whether such a correlation exists between neurones from the medullary raphe (a chemosensitive brain region) and hippocampus (a non-chemosensitive region), we used BCECF to monitor pH(i) in cultured neurones subjected to extracellular acid-base disturbances. In medullary raphe neurones, respiratory acidosis (5%--> 9% CO(2)) caused a rapid fall in pH(i) (DeltapH(i) approximately 0.2) with no recovery and a large DeltapH(i)/DeltapH(o) of 0.71. Hippocampal neurones had a similar response, but with a slightly lower DeltapH(i)/DeltapH(o) (0.59). We further investigated a possible link between pH(i) regulation and chemosensitivity by following the pH(i) measurements on medullary raphe neurones with an immunocytochemistry for tryptophan hydroxylase (a marker of serotonergic neurones). We found that the DeltapH(i)/DeltapH(o) of 0.69 for serotonergic neurones (which are stimulated by acidosis) was not different from either the DeltapH(i)/DeltapH(o) of 0.75 for non-serotonergic neurones (most of which are not chemosensitive), or from the DeltapH(i)/DeltapH(o) of hippocampal neurones. For both respiratory alkalosis (5%--> 3% CO(2)) and metabolic alkalosis (22 mm--> 35 mm HCO(3)(-)), DeltapH(i)/DeltapH(o) was 0.42-0.53 for all groups of neurones studied. The only notable difference between medullary raphe and hippocampal neurones was in response to metabolic acidosis (22 mm--> 14 mm HCO(3)(-)), which caused a large pH(i) decrease in approximately 80% of medullary raphe neurones (DeltapH(i)/DeltapH(o)= 0.71), but relatively little pH(i) decrease in 70% of the hippocampal neurones (DeltapH(i)/DeltapH(o)= 0.09). Our comparison of medullary raphe and hippocampal neurones indicates that, except in response to metabolic acidosis, the neurones from the chemosensitive region do not have a uniquely high DeltapH(i)/DeltapH(o). Moreover, regardless of whether neurones were cultured from the chemosensitive or the non-chemosensitive region, pH(i) did not recover during any of the acid-base stresses.

Acidosis, Respiratory↗

PubMed2004

Multiple benefits of carbon-friendly agricultural practices: empirical assessment of conservation tillage.

This study empirically estimates the multiple benefits of a subsidy policy that would offer payments to farmers in return for the adoption of conservation tillage, and compares the outcomes of alternative targeting designs for such a policy. The least-cost incentive payment policy schemes are simulated for the State of Iowa by using the data for roughly 12,000 National Resource Inventory (NRI) points. We use an economic conservation tillage adoption model to evaluate the costs of adoption and a physical process simulation model (EPIC) to estimate the environmental benefits due to adoption at each of the NRI points. Two targeting options are considered. We assess the costs and environmental consequences of a practice-based policy instrument (which maximizes the acres of land in conservation tillage, regardless of its level of environmental benefits) and contrast it to a performance-based instrument (which yields the highest amount of environmental benefits per dollar spent). Carbon sequestration in agricultural soils, reduction of soil erosion by wind and water, and the reduction in nitrogen runoff are considered as possible targets for the performance-based instruments. We find that the practice-based instrument provides high proportions of the four benefits relative to the policies that target the benefits directly, especially at the higher policy budget levels. Similarly, we estimate that targeting one of the four benefits individually provides high percentages of the other benefits as compared with the amounts of the benefits obtainable if they were targeted directly.

Agriculture↗

PubMed2003

Effect of isolated removal of either basolateral HCO-3 or basolateral CO2 on HCO-3 reabsorption by rabbit S2 proximal tubule.

The equilibrium CO2+H2O right arrow over left arrow H++HCO3- had made it impossible to determine how isolated changes in basolateral CO2 ([CO2]) or HCO3- concentration ([HCO3-]), at a fixed basolateral pH, modulate renal HCO3- or reabsorption. In the present study, we have begun to address this issue by measuring HCO3- reabsorption (JHCO3) and intracellular pH (pHi) in isolated perfused rabbit S2 proximal tubules exposed to three different basolateral (bath) solutions: 1) equilibrated 5% CO2/22 mM HCO3-/pH 7.40, 2) an out-of-equilibrium (OOE) solution containing 5% CO2/pH 7.40 but minimal HCO3- ("pure CO2"), and 3) an OOE solution containing 22 mM HCO3-/pH 7.40 but minimal CO2 ("pure HCO3-"). Tubule lumens were constantly perfused with equilibrated 5% CO2/22 mM HCO3-. Compared with the equilibrated bath solution (JHCO3 = 76.5 +/- 7.7 pmol.min-1.mm-1, pHi = 7.09 +/- 0.04), the pure CO2 bath solution increased JHCO3 by approximately 25% but decreased pHi by 0.19. In contrast, the pure HCO3- bath solution decreased JHCO3 by 37% but increased pHi by 0.24. Our data are consistent with two competing hypotheses: 1) the isolated removal of basolateral HCO3- (or CO2) causes a pHi decrease (increase) that in turn raises (lowers) JHCO3; and 2) HCO3- removal raises JHCO3 by reducing inhibition of basolateral Na/HCO3 cotransport and/or reducing HCO3- backleak, whereas CO2 removal lowers JHCO3 by reducing stimulation of a CO2 sensor.

Acid-Base Equilibrium↗