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Mistargeting of a truncated Na-K-2Cl cotransporter in epithelial cells.
Koumangoye R, Omer S, Delpire E
(2018) Am J Physiol Cell Physiol 315: C258-C276
MeSH Terms: Animals, Cell Membrane, Cells, Cultured, Colon, Cytoplasm, Dogs, Epithelial Cells, Female, Madin Darby Canine Kidney Cells, Male, Mice, Oocytes, Salivary Glands, Sodium-Potassium-Chloride Symporters, Sodium-Potassium-Exchanging ATPase, Solute Carrier Family 12, Member 2, Xenopus laevis
Show Abstract · Added May 4, 2018
We recently reported the case of a young patient with multisystem failure carrying a de novo mutation in SLC12A2, the gene encoding the Na-K-2Cl cotransporter-1 (NKCC1). Heterologous expression studies in nonepithelial cells failed to demonstrate dominant-negative effects. In this study, we examined expression of the mutant cotransporter in epithelial cells. Using Madin-Darby canine kidney (MDCK) cells grown on glass coverslips, permeabilized support, and Matrigel, we show that the fluorescently tagged mutant cotransporter is expressed in cytoplasm and at the apical membrane and affects epithelium integrity. Expression of the mutant transporter at the apical membrane also results in the mislocalization of some of the wild-type transporter to the apical membrane. This mistargeting is specific to NKCC1 as the Na-K-ATPase remains localized on the basolateral membrane. To assess transporter localization in vivo, we created a mouse model using CRISPR/cas9 that reproduces the 11 bp deletion in exon 22 of Slc12a2. Although the mice do not display an overt phenotype, we show that the colon and salivary gland expresses wild-type NKCC1 abundantly at the apical pole, confirming the data obtained in cultured epithelial cells. Enough cotransporter must remain, however, on the basolateral membrane to participate in saliva secretion, as no significant decrease in saliva production was observed in the mutant mice.
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17 MeSH Terms
Functional features of the "finger" domain of the DEG/ENaC channels MEC-4 and UNC-8.
Matthewman C, Johnson CK, Miller DM, Bianchi L
(2018) Am J Physiol Cell Physiol 315: C155-C163
MeSH Terms: Amino Acid Sequence, Animals, Calcium, Cell Death, Cell Membrane Permeability, Epithelial Sodium Channels, Magnesium, Membrane Proteins, Mutation, Oocytes, Protein Transport, Sodium, Xenopus laevis
Show Abstract · Added March 26, 2019
UNC-8 and MEC-4 are two members of the degenerin/epithelial Na channel (DEG/ENaC) family of voltage-independent Na channels that share a high degree of sequence homology and functional similarity. For example, both can be hyperactivated by genetic mutations [UNC-8(d) and MEC-4(d)] that induce neuronal death by necrosis. Both depend in vivo on chaperone protein MEC-6 for function, as demonstrated by the finding that neuronal death induced by hyperactive UNC-8 and MEC-4 channels is prevented by null mutations in mec-6. UNC-8 and MEC-4 differ functionally in three major ways: 1) MEC-4 is calcium permeable, whereas UNC-8 is not; 2) UNC-8, but not MEC-4, is blocked by extracellular calcium and magnesium in the micromolar range; and 3) MEC-6 increases the number of MEC-4 channels at the cell surface in oocytes but does not have this effect on UNC-8. We previously reported that Capermeability of MEC-4 is conferred by the second transmembrane domain. We show here that the extracellular "finger" domain of UNC-8 is sufficient to mediate inhibition by divalent cations and that regulation by MEC-6 also depends on this region. Thus, our work confirms that the finger domain houses residues involved in gating of this channel class and shows for the first time that the finger domain also mediates regulation by chaperone protein MEC-6. Given that the finger domain is the most divergent region across the DEG/ENaC family, we speculate that it influences channel trafficking and function in a unique manner depending on the channel subunit.
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13 MeSH Terms
Reconstitution of the Cytoplasmic Regulation of the Wnt Signaling Pathway Using Xenopus Egg Extracts.
Hyde AS, Hang BI, Lee E
(2016) Methods Mol Biol 1481: 101-9
MeSH Terms: Animals, Cell Cycle, Chromatin Assembly and Disassembly, DNA Replication, Embryonic Development, Microtubules, Molecular Biology, Oocytes, Proteolysis, Wnt Proteins, Wnt Signaling Pathway, Xenopus laevis, beta Catenin
Show Abstract · Added February 13, 2017
The regulation of β-catenin turnover is the central mechanism governing activation of the Wnt signaling pathway. All components of the pathway are present in the early embryo of Xenopus laevis, and Xenopus egg extracts have been used to recapitulate complex biological reactions such as microtubule dynamics, DNA replication, chromatin assembly, and phases of the cell cycle. Herein, we describe a biochemical method for analyzing β-catenin degradation using radiolabeled and luciferase-fusion proteins in Xenopus egg extracts. We show that in such a biochemical system, cytoplasmic β-catenin degradation is regulated by soluble components of the Wnt pathway as well as small molecules.
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13 MeSH Terms
Modeling the roles of protein kinase Cβ and η in single-cell wound repair.
Holmes WR, Liao L, Bement W, Edelstein-Keshet L
(2015) Mol Biol Cell 26: 4100-8
MeSH Terms: Actin Cytoskeleton, Actins, Animals, Models, Biological, Oocytes, Protein Kinase C, Protein Kinase C beta, Single-Cell Analysis, Wound Healing, Xenopus laevis, rho GTP-Binding Proteins
Show Abstract · Added February 26, 2016
Wounded cells such as Xenopus oocytes respond to damage by assembly and closure of an array of actin filaments and myosin-2 controlled by Rho GTPases, including Rho and Cdc42. Rho and Cdc42 are patterned around wounds in a characteristic manner, with active Rho concentrating in a ring-like zone inside a larger, ring-like zone of active Cdc42. How this patterning is achieved is unknown, but Rho and Cdc42 at wounds are subject to regulation by other proteins, including the protein kinases C. Specifically, Cdc42 and Rho activity are enhanced by PKCβ and inhibited by PKCη. We adapt a mathematical model of Simon and coworkers to probe the possible roles of these kinases. We show that PKCβ likely affects the magnitude of positive Rho-Abr feedback, whereas PKCη acts on Cdc42 inactivation. The model explains both qualitative and some overall quantitative features of PKC-Rho GTPase regulation. It also accounts for the previous, peculiar observation that ∼ 20% of cells overexpressing PKCη display zone inversions--that is, displacement of active Rho to the outside of the active Cdc42.
© 2015 Holmes, Liao, et al. This article is distributed by The American Society for Cell Biology under license from the author(s). Two months after publication it is available to the public under an Attribution–Noncommercial–Share Alike 3.0 Unported Creative Commons License (http://creativecommons.org/licenses/by-nc-sa/3.0).
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Antennal-expressed ammonium transporters in the malaria vector mosquito Anopheles gambiae.
Pitts RJ, Derryberry SL, Pulous FE, Zwiebel LJ
(2014) PLoS One 9: e111858
MeSH Terms: Animals, Anopheles, Arthropod Antennae, Cation Transport Proteins, Genes, Insect, Genetic Complementation Test, Injections, Insect Proteins, Insect Vectors, Ion Channel Gating, Malaria, Mutation, Oocytes, Phylogeny, Protein Structure, Tertiary, RNA, Messenger, Saccharomyces cerevisiae, Xenopus
Show Abstract · Added February 19, 2015
The principal Afrotropical malaria vector mosquito, Anopheles gambiae remains a significant threat to human health. In this anthropophagic species, females detect and respond to a range of human-derived volatile kairomones such as ammonia, lactic acid, and other carboxylic acids in their quest for blood meals. While the molecular underpinnings of mosquito olfaction and host seeking are becoming better understood, many questions remain unanswered. In this study, we have identified and characterized two candidate ammonium transporter genes, AgAmt and AgRh50 that are expressed in the mosquito antenna and may contribute to physiological and behavioral responses to ammonia, which is an important host kairomone for vector mosquitoes. AgAmt transcripts are highly enhanced in female antennae while a splice variant of AgRh50 appears to be antennal-specific. Functional expression of AgAmt in Xenopus laevis oocytes facilitates inward currents in response to both ammonium and methylammonium, while AgRh50 is able to partially complement a yeast ammonium transporter mutant strain, validating their conserved roles as ammonium transporters. We present evidence to suggest that both AgAmt and AgRh50 are in vivo ammonium transporters that are important for ammonia sensitivity in An. gambiae antennae, either by clearing ammonia from the sensillar lymph or by facilitating sensory neuron responses to environmental exposure. Accordingly, AgAmt and AgRh50 represent new and potentially important targets for the development of novel vector control strategies.
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18 MeSH Terms
Short forms of Ste20-related proline/alanine-rich kinase (SPAK) in the kidney are created by aspartyl aminopeptidase (Dnpep)-mediated proteolytic cleavage.
Markadieu N, Rios K, Spiller BW, McDonald WH, Welling PA, Delpire E
(2014) J Biol Chem 289: 29273-84
MeSH Terms: Amino Acid Sequence, Animals, Blood Pressure, Cloning, Molecular, Glutamyl Aminopeptidase, Humans, Kidney, Kidney Medulla, Mass Spectrometry, Metalloproteases, Mice, Mice, Inbred C57BL, Molecular Sequence Data, Oocytes, Protein Binding, Protein Structure, Secondary, Protein-Serine-Threonine Kinases, Recombinant Fusion Proteins, Signal Transduction, Sodium, Xenopus laevis
Show Abstract · Added October 21, 2014
The Ste20-related kinase SPAK regulates sodium, potassium, and chloride transport in a variety of tissues. Recently, SPAK fragments, which lack the catalytic domain and are inhibitory to Na(+) transporters, have been detected in kidney. It has been hypothesized that the fragments originate from alternative translation start sites, but their precise origin is unknown. Here, we demonstrate that kidney lysate possesses proteolytic cleavage activity toward SPAK. Ion exchange and size exclusion chromatography combined with mass spectrometry identified the protease as aspartyl aminopeptidase. The presence of the protease was verified in the active fractions, and recombinant aspartyl aminopeptidase recapitulated the cleavage pattern observed with kidney lysate. Identification of the sites of cleavage by mass spectrometry allowed us to test the function of the smaller fragments and demonstrate their inhibitory action toward the Na(+)-K(+)-2Cl(-) cotransporter, NKCC2.
© 2014 by The American Society for Biochemistry and Molecular Biology, Inc.
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21 MeSH Terms
Missense dopamine transporter mutations associate with adult parkinsonism and ADHD.
Hansen FH, Skjørringe T, Yasmeen S, Arends NV, Sahai MA, Erreger K, Andreassen TF, Holy M, Hamilton PJ, Neergheen V, Karlsborg M, Newman AH, Pope S, Heales SJ, Friberg L, Law I, Pinborg LH, Sitte HH, Loland C, Shi L, Weinstein H, Galli A, Hjermind LE, Møller LB, Gether U
(2014) J Clin Invest 124: 3107-20
MeSH Terms: Adult, Amino Acid Sequence, Amino Acid Substitution, Animals, Attention Deficit Disorder with Hyperactivity, Brain, Cohort Studies, DNA Mutational Analysis, Dopamine, Dopamine Plasma Membrane Transport Proteins, Female, HEK293 Cells, Humans, Male, Models, Molecular, Molecular Sequence Data, Mutant Proteins, Mutation, Missense, Oocytes, Parkinsonian Disorders, Pedigree, Positron-Emission Tomography, Protein Conformation, Recombinant Proteins, Sequence Homology, Amino Acid, Sodium, Tomography, Emission-Computed, Single-Photon, Xenopus
Show Abstract · Added February 19, 2015
Parkinsonism and attention deficit hyperactivity disorder (ADHD) are widespread brain disorders that involve disturbances of dopaminergic signaling. The sodium-coupled dopamine transporter (DAT) controls dopamine homeostasis, but its contribution to disease remains poorly understood. Here, we analyzed a cohort of patients with atypical movement disorder and identified 2 DAT coding variants, DAT-Ile312Phe and a presumed de novo mutant DAT-Asp421Asn, in an adult male with early-onset parkinsonism and ADHD. According to DAT single-photon emission computed tomography (DAT-SPECT) scans and a fluoro-deoxy-glucose-PET/MRI (FDG-PET/MRI) scan, the patient suffered from progressive dopaminergic neurodegeneration. In heterologous cells, both DAT variants exhibited markedly reduced dopamine uptake capacity but preserved membrane targeting, consistent with impaired catalytic activity. Computational simulations and uptake experiments suggested that the disrupted function of the DAT-Asp421Asn mutant is the result of compromised sodium binding, in agreement with Asp421 coordinating sodium at the second sodium site. For DAT-Asp421Asn, substrate efflux experiments revealed a constitutive, anomalous efflux of dopamine, and electrophysiological analyses identified a large cation leak that might further perturb dopaminergic neurotransmission. Our results link specific DAT missense mutations to neurodegenerative early-onset parkinsonism. Moreover, the neuropsychiatric comorbidity provides additional support for the idea that DAT missense mutations are an ADHD risk factor and suggests that complex DAT genotype and phenotype correlations contribute to different dopaminergic pathologies.
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28 MeSH Terms
Data from artificial models of mitochondrial DNA disorders are not always applicable to humans.
Steffann J, Gigarel N, Samuels DC, Monnot S, Borghese R, Hesters L, Frydman N, Burlet P, Frydman R, Benachi A, Rotig A, Munnich A, Bonnefont JP
(2014) Cell Rep 7: 933-4
MeSH Terms: Animals, Blastocyst, Cell Division, DNA, Mitochondrial, Embryonic Development, Female, Haplotypes, Macaca mulatta, Oocytes, Pregnancy
Added May 27, 2014
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Molecular and functional characterization of Anopheles gambiae inward rectifier potassium (Kir1) channels: a novel role in egg production.
Raphemot R, Estévez-Lao TY, Rouhier MF, Piermarini PM, Denton JS, Hillyer JF
(2014) Insect Biochem Mol Biol 51: 10-9
MeSH Terms: Amino Acid Sequence, Animals, Anopheles, Base Sequence, Female, Molecular Sequence Data, Oocytes, Ovary, Ovum, Potassium Channels, Inwardly Rectifying, Pupa, RNA Interference, Xenopus laevis
Show Abstract · Added February 5, 2016
Inward rectifier potassium (Kir) channels play essential roles in regulating diverse physiological processes. Although Kir channels are encoded in mosquito genomes, their functions remain largely unknown. In this study, we identified the members of the Anopheles gambiae Kir gene family and began to investigate their function. Notably, we sequenced the A. gambiae Kir1 (AgKir1) gene and showed that it encodes all the canonical features of a Kir channel: an ion pore that is composed of a pore helix and a selectivity filter, two transmembrane domains that flank the ion pore, and the so-called G-loop. Heterologous expression of AgKir1 in Xenopus oocytes revealed that this gene encodes a functional, barium-sensitive Kir channel. Quantitative RT-PCR experiments then showed that relative AgKir1 mRNA levels are highest in the pupal stage, and that AgKir1 mRNA is enriched in the adult ovaries. Gene silencing of AgKir1 by RNA interference did not affect the survival of female mosquitoes following a blood meal, but decreased their egg output. These data provide evidence for a new role of Kir channels in mosquito fecundity, and further validates them as promising molecular targets for the development of a new class of mosquitocides to be used in vector control.
Copyright © 2014 Elsevier Ltd. All rights reserved.
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13 MeSH Terms
Neurosensory perception of environmental cues modulates sperm motility critical for fertilization.
McKnight K, Hoang HD, Prasain JK, Brown N, Vibbert J, Hollister KA, Moore R, Ragains JR, Reese J, Miller MA
(2014) Science 344: 754-7
MeSH Terms: Animals, Caenorhabditis elegans, Caenorhabditis elegans Proteins, Environmental Exposure, Female, Fertilization, Male, Neurons, Afferent, Neurosecretory Systems, Oocytes, Ovum, Perception, Pheromones, Prostaglandin-Endoperoxide Synthases, Prostaglandins, Sperm Motility, Spermatozoa, Transforming Growth Factor beta
Show Abstract · Added May 19, 2014
Environmental exposures affect gamete function and fertility, but the mechanisms are poorly understood. Here, we show that pheromones sensed by ciliated neurons in the Caenorhabditis elegans nose alter the lipid microenvironment within the oviduct, thereby affecting sperm motility. In favorable environments, pheromone-responsive sensory neurons secrete a transforming growth factor-β ligand called DAF-7, which acts as a neuroendocrine factor that stimulates prostaglandin-endoperoxide synthase [cyclooxygenase (Cox)]-independent prostaglandin synthesis in the ovary. Oocytes secrete F-class prostaglandins that guide sperm toward them. These prostaglandins are also synthesized in Cox knockout mice, raising the possibility that similar mechanisms exist in other animals. Our data indicate that environmental cues perceived by the female nervous system affect sperm function.
Copyright © 2014, American Association for the Advancement of Science.
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18 MeSH Terms