The authors are deeply indebted to all the members of the scientific community working on pH and ion transport, who have originated and improved the measurements described here. They particularly thank Dr. Jacques Pouyss&#233;gur who originated the H+-killing selection technique used here. They acknowledge the University of Nice-Sophia Antipolis, the CNRS, the ANR (JCJC SVSE1 NHEint) and the ICST Labex for support.

1. H+ Killing Selection
<ol>
	<li>Cell lines
	<ol>
		<li>Stably transfect NHE-deficient cells (e.g., the CCL39-derived PS120 cell line16) using any combination of mammalian expression vector and transfection method that will produce efficient transfection yields and selection in a fibroblast cell line. 
		NOTE: For many years Calcium Phosphate precipitation19 was used with good transfection yields. This has been replaced more recently by commercial reagents such as Lipofec...

<ol>
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J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chloride+and+the+endosomal-lysosomal+pathway:+emerging+roles+of+CLC+chloride+transporters.">Chloride and the endosomal-lysosomal pathway: emerging roles of CLC chloride transporters.</a> J Physiol. 578 (3), 633-640 (2007).</li><li>Kornak, U., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mutations+in+the+a3+subunit+of+the+vacuolar+H(+)-ATPase+cause+infantile+malignant+osteopetrosis.">Mutations in the a3 subunit of the vacuolar H(+)-ATPase cause infantile malignant osteopetrosis.</a> Hum Mol Genet. 9 (13), 2059-2063 (2000).</li><li>Gunther, W., Piwon, N., Jentsch, T. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+ClC-5+chloride+channel+knock-out+mouse+-+an+animal+model+for+Dent's+disease.">The ClC-5 chloride channel knock-out mouse - an animal model for Dent's disease.</a> Pflugers Arch. 445 (4), 456-462 (2003).</li><li>Kasper, D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Loss+of+the+chloride+channel+ClC-7+leads+to+lysosomal+storage+disease+and+neurodegeneration.">Loss of the chloride channel ClC-7 leads to lysosomal storage disease and neurodegeneration.</a> Embo J. 24 (5), 1079-1091 (2005).</li><li>Poet, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Lysosomal+storage+disease+upon+disruption+of+the+neuronal+chloride+transport+protein+ClC-6.">Lysosomal storage disease upon disruption of the neuronal chloride transport protein ClC-6.</a> Proc Natl Acad Sci U S A. 103 (37), 13854-13859 (2006).</li><li>Nakamura, N., Tanaka, S., Teko, Y., Mitsui, K., Kanazawa, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Four+Na+/H++exchanger+isoforms+are+distributed+to+Golgi+and+post-Golgi+compartments+and+are+involved+in+organelle+pH+regulation.">Four Na+/H+ exchanger isoforms are distributed to Golgi and post-Golgi compartments and are involved in organelle pH regulation.</a> J Biol Chem. 280 (2), 1561-1572 (2005).</li><li>Gilfillan, G. D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=SLC9A6+mutations+cause+X-linked+mental+retardation,+microcephaly,+epilepsy,+and+ataxia,+a+phenotype+mimicking+Angelman+syndrome.">SLC9A6 mutations cause X-linked mental retardation, microcephaly, epilepsy, and ataxia, a phenotype mimicking Angelman syndrome.</a> Am J Hum Genet. 82 (4), 1003-1010 (2008).</li><li>Mignot, C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Novel+mutation+in+SLC9A6+gene+in+a+patient+with+Christianson+syndrome+and+retinitis+pigmentosum.">Novel mutation in SLC9A6 gene in a patient with Christianson syndrome and retinitis pigmentosum.</a> Brain &amp; Development. 35 (2), 172-176 (2013).</li><li>Morrow, E. 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A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+large+scale+multivariate+parallel+ICA+method+reveals+novel+imaging-genetic+relationships+for+Alzheimer's+disease+in+the+ADNI+cohort.">A large scale multivariate parallel ICA method reveals novel imaging-genetic relationships for Alzheimer's disease in the ADNI cohort.</a> Neuroimage. 60 (3), 1608-1621 (2012).</li><li>Zhang, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+microdeletion+in+Xp11.3+accounts+for+co-segregation+of+retinitis+pigmentosa+and+mental+retardation+in+a+large+kindred.">A microdeletion in Xp11.3 accounts for co-segregation of retinitis pigmentosa and mental retardation in a large kindred.</a> Am J Med Genet A. 140 (4), 349-357 (2006).</li><li>Sardet, C., Franchi, A., Pouyss&#233;gur, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Molecular+cloning,+primary+structure,+and+expression+of+the+human+growth+factor-activatable+Na+/H++antiporter.">Molecular cloning, primary structure, and expression of the human growth factor-activatable Na+/H+ antiporter.</a> Cell. 56 (2), 271-280 (1989).</li><li>Pouyssegur, J., Sardet, C., Franchi, A., L'Allemain, G., Paris, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+specific+mutation+abolishing+Na+/H++antiport+activity+in+hamster+fibroblasts+precludes+growth+at+neutral+and+acidic+pH.">A specific mutation abolishing Na+/H+ antiport activity in hamster fibroblasts precludes growth at neutral and acidic pH.</a> Proc Natl Acad Sci U S A. 81 (15), 4833-4837 (1984).</li><li>Franchi, A., Cragoe, E., Pouyss&#233;gur, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Isolation+and+properties+of+fibroblast+mutants+overexpressing+an+altered+Na+/H++antiporter.">Isolation and properties of fibroblast mutants overexpressing an altered Na+/H+ antiporter.</a> J Biol Chem. 261 (31), 14614-14620 (1986).</li><li>Milosavljevic, N., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+Intracellular+Na+/H++Exchanger+NHE7+effects+a+Na++coupled,+but+not+K++coupled+proton-loading+mechanism+in+endocytosis.">The Intracellular Na+/H+ Exchanger NHE7 effects a Na+ coupled, but not K+ coupled proton-loading mechanism in endocytosis.</a> Cell Reports. 7 (3), 1-8 (2014).</li><li>Wigler, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Transformation+of+mammalian+cells+with+genes+from+procaryotes+and+eucaryotes.">Transformation of mammalian cells with genes from procaryotes and eucaryotes.</a> Cell. 16 (4), 777-785 (1979).</li><li>Lacroix, J., Po&#235;t, M., Maherel, C., Counillon, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+mechanism+for+the+activation+of+the+Na/H+exchanger+NHE-1+by+cytoplasmic+acidification+and+mitogens.">A mechanism for the activation of the Na/H exchanger NHE-1 by cytoplasmic acidification and mitogens.</a> EMBO Reports. 5 (1), 91-96 (2004).</li><li>Milosavljevic, N., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nongenomic+Effects+of+Cisplatin:+Acute+Inhibition+of+Mechanosensitive+Transporters+and+Channels+without+Actin+Remodeling.">Nongenomic Effects of Cisplatin: Acute Inhibition of Mechanosensitive Transporters and Channels without Actin Remodeling.</a> Cancer Res. 70 (19), 7514-7522 (2010).</li><li>Boron, W. 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This protocol describes how to select cells expressing intracellular Na+/H+ exchangers at the plasma membrane without altering their primary sequence by site-directed mutagenesis. These exchangers can now be characterized.
This method is based on the cellular toxicity of intracellular protons to select cell lines that will express vesicular Na+/H+ exchangers at the plasma membrane. It might be possible, in principle, to use other cations that may be ...

Most intracellular compartments display an acidic luminal pH, which is a key parameter for maturation, trafficking, recycling of proteins or hormones and neurotransmitters loading. It has been shown that the pH gradient between cytosol and vesicular content is generated by vacuolar H+ ATPases1, coupled to vesicular ClC chloride transporters2. Both in knock-out (KO) mice and human patients, the importance of these transporters has been highlighted by the heavy phenotypes caused by mutations in their genes3-6.
The members of the Sodium-Hydrogen exchangers SLC9A family, also termed NHEs for Na+/H+ exchangers, have been shown to be key effectors in intracellular pH and cell volume regulation, as well as in vectorial transport of acid-base equivalents across epithelia. Besides the plasma membrane NHEs, three highly conserved Na+/H+ exchangers, NHE 6, 7 and 9 are expressed in trans-Golgi network and in early endosomes7. Mutations in their genes have been linked with Angelman-like or Christianson Syndromes8-9, family-based autism10 and Attention Deficit Hyperactivity Disorder11-12. These exchangers have also been involved in neurodegenerative problems such as Alzheimer disease susceptibility13 and X-linked mental retardation contiguous genes syndromes14. Taken together, these studies highlight the importance of these intracellular NHEs in brain development and/or function.
The intracellular localization of these exchangers prevents accurate measurements of their ion selectivity, transport direction, kinetic parameters, and regulation. As is the case for all transporters expressed in intracellular compartments, it is extremely difficult to assess their biochemical activities and hence to fully understand their physiological roles and the mechanisms underlying their pathological implications. Based on the high cytosolic K+ concentration, the most-commonly accepted hypothesis was that they were working as K+ coupled proton efflux transporters. The existence of such a proton leak had been hypothesized, as it may counterbalance proton pumping by the V-ATPases in order to maintain a steady state vesicular pH. The aim of this visual article is (i) to demonstrate a method that allows the genetic selection of cell lines that express such vesicular transporters at their plasma membrane, and (ii) to show two independent approaches to measure the functions of these transporters.
Three decades ago, Pouyss&#233;gur and Franchi have pioneered a genetic approach that enabled the molecular cloning and characterization of the members of the NHE family15. This was based on the toxicity of intracellular protons as a screening method. The first step was to obtain cell lines deficient in any Na+/H+ exchange expressed at the plasma membrane, using the reversibility of this transporter. Fibroblasts (CCL39 cell line) were preloaded with Na+ or Li+ and then placed in an acidic extracellular medium (pH 6.5) for 2 hr. This led to the death of cells expressing a functional Na+/H+ exchange and to the selection of antiporter-deficient cells (PS120 cell line)16. When cultivated in bicarbonate-free medium, these cells are very sensitive to acute intracellular acidification. Consequently, the expression of any functional proton efflux mechanism at the plasma membrane will be positively selected (see17) if such cells are submitted to acute intracellular acidifications. Such acidification techniques can be used to isolate cell lines with trafficking defects enabling the forced expression of WT intracellular NHEs at the plasma membrane.
As eukaryotic Na+/H+ exchangers are electroneutral, they are not measurable by the electrophysiological approaches that have been used with great success to measure channels. This manuscript therefore demonstrates how to measure the activity of this exchanger by intracellular pH measurements and rapid kinetics of lithium uptake. As the underlying concepts are the same, it is interesting to notice that many of the processes developed for the selection section are also used directly for functional measurements.
Interestingly, we have observed that the trafficking defect present in the cell lines selected using the approach described in this manuscript leads to a greater expression of other vesicular proteins at the plasma membrane such as the vesicular potassium channel TWIK118. This points out toward the selection of a general retention defect mechanism for vesicular transmembrane proteins. Hence this selection procedure and the cells that it generates may constitute a promising tool for the scientific community working on the membrane proteins of intracellular compartments. As well the measurement techniques presented here might be applicable for studying other non-electrogenic transporters.

<table border="0" cellpadding="0" cellspacing="0" width="621">
	<tbody>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Name of Material/ Equipment</td>
			<td style="width:119px;">Company</td>
			<td style="width:119px;">Catalog Number</td>
			<td style="width:167px;">Comments/Description</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;"></td>
			<td style="width:119px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Standard cell culture equipement</td>
			<td style="width:119px;"></td>
			<td style="width:119px;"></td>
			<td>Used for H+ killing selection composed of many devices with different catalog numbers</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Incubator with CO2</td>
			<td style="width:119px;">Sanyo</td>
			<td style="width:119px;">MCO15A</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Incubator without CO2</td>
			<td style="width:119px;">Heraeus instrument</td>
			<td style="width:119px;">BB6220</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Laminar flow hood PSM1200NF</td>
			<td style="width:119px;">Fisher&#160;</td>
			<td style="width:119px;">52010120</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">DMEM medium</td>
			<td style="width:119px;">sigma</td>
			<td style="width:119px;">D5796</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">FBS gold</td>
			<td style="width:119px;">GE Healthcare</td>
			<td style="width:119px;">A15-151</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Penicilin/streptomycin</td>
			<td style="width:119px;">PAA</td>
			<td>P11-010</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Trypsin 10X</td>
			<td style="width:119px;">PAA</td>
			<td style="width:119px;">L11-003</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;"></td>
			<td style="width:119px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;"></td>
			<td style="width:119px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:216px;">Atomic Absorption spectrometer with Zeeman furnace system</td>
			<td style="width:119px;">Thermo Scientific</td>
			<td style="width:119px;">ICE 3500 GFZ</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">LiCl</td>
			<td style="width:119px;">sigma</td>
			<td style="width:119px;">L4408</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Nitric Acid</td>
			<td style="width:119px;">sigma</td>
			<td align="right" style="width:119px;">438073</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;"></td>
			<td style="width:119px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Fluorescence videomicroscopy set</td>
			<td style="width:119px;">Leica</td>
			<td style="width:119px;"></td>
			<td>Composed of many devices with different catalog numbers</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;"></td>
			<td style="width:119px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Inverted automated microscope</td>
			<td style="width:119px;">Leica</td>
			<td style="width:119px;">DMI6000B</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">microscope stand</td>
			<td style="width:119px;">leica</td>
			<td align="right" style="width:119px;">11888906</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;"></td>
			<td style="width:119px;"></td>
			<td align="right" style="width:119px;">11888911</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;"></td>
			<td style="width:119px;"></td>
			<td align="right" style="width:119px;">11505180</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;"></td>
			<td style="width:119px;"></td>
			<td align="right" style="width:119px;">11888377</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">incident fluorescence</td>
			<td style="width:119px;">leica</td>
			<td align="right" style="width:119px;">11888901</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;"></td>
			<td style="width:119px;"></td>
			<td align="right" style="width:119px;">11504166</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">motor bracket</td>
			<td style="width:119px;">leica</td>
			<td align="right" style="width:119px;">11888379</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;"></td>
			<td style="width:119px;"></td>
			<td align="right" style="width:119px;">11505234</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;"></td>
			<td style="width:119px;"></td>
			<td align="right" style="width:119px;">11521505</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;"></td>
			<td style="width:119px;"></td>
			<td align="right" style="width:119px;">11522106</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">LED transmission light&#160;</td>
			<td style="width:119px;">leica</td>
			<td align="right" style="width:119px;">8097321</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;"></td>
			<td style="width:119px;"></td>
			<td align="right" style="width:119px;">8102034</td>
			<td></td>
		</tr>
		<tr height="21">
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functional characterization of na+/h+ exchangers of intracellular compartments using proton-killing selection to express them at the plasma membrane

Endosomal acidification is critical for a wide range of processes, such as protein recycling and degradation, receptor desensitization, and neurotransmitter loading in synaptic vesicles. This acidification is described to be mediated by proton ATPases, coupled to ClC chloride transporters. Highly-conserved electroneutral protons transporters, the Na+/H+ exchangers (NHE) 6, 7 and 9 are also expressed in these compartments. Mutations in their genes have been linked with human cognitive and neurodegenerative diseases. Paradoxically, their roles remain elusive, as their intracellular localization has prevented detailed functional characterization. This manuscript shows a method to solve this problem. This consists of the selection of mutant cell lines, capable of surviving acute cytosolic acidification by retaining intracellular NHEs at the plasma membrane. It then depicts two complementary protocols to measure the ion selectivity and activity of these exchangers: (i) one based on intracellular pH measurements using fluorescence video microscopy, and (ii) one based on the fast kinetics of lithium uptake. Such protocols can be extrapolated to measure other non-electrogenic transporters. Furthermore, the selection procedure presented here generates cells with an intracellular retention defective phenotype. Therefore these cells will also express other vesicular membrane proteins at the plasma membrane. The experimental strategy depicted here may therefore constitute a potentially powerful tool to study other intracellular proteins that will be then expressed at the plasma membrane together with the vesicular Na+/H+ exchangers used for the selection.

Selection:
The H+ killing selection is based on the diffusion of the ammonium weak base, as depicted in Figure 1A. The effect of weak bases and acids diffusion on intracellular pH has been pioneered by Walter Boron and collaborators22. The elegant idea to use this phenomenon to produce a lethal acidification for positive genetic selection was then developed by Jacques Pouyss&#233;gur17. Under such a protocol, the intracellular pH drops to about...

Watch this Scientific Journal Video about Functional Characterization of Na+/H+ Exchangers of Intracellular Compartments Using Proton-killing Selection to Express Them at the Plasma Membrane at JoVE.c

Functional Characterization of Na+/H+ Exchangers of Intracellular Compartments Using Proton-killing Selection to Express Them at the Plasma Membrane

The first part of this article shows how to select mutant cell lines expressing vesicular Na+/H+ exchangers at their plasma membrane. The second part provides protocols based on intracellular pH measurements and fast ion uptake, which are used to determine the ion selectivity and the kinetic parameters of these exchangers.

Functional Characterization of Na+/H+ Exchangers of Intracellular Compartments Using Proton-killing Selection to Express Them at the Plasma Membrane

Endosomal acidification is critical for a wide range of processes, such as protein recycling and degradation, receptor desensitization, and ...

functional-characterization-na-h-exchangers-intracellular

Research

JoVE Journal

Biology

9.2K Views.  Université Nice-Sophia Antipolis, Laboratoire de Physiomédecine Moléculaire, CNRS UMR7370, and Laboratories of Excellence Ion Channel Science and Therapeutics. The first part of this article shows how to select mutant cell lines expressing vesicular Na+/H+ exchangers at their plasma membrane. The second part provides protocols based on intracellular pH measurements and fast ion uptake, which are used to determine the ion selectivity and the kinetic parameters of these exchangers. 

Video: Functional Characterization of Na+/H+ Exchangers of Intracellular Compartments Using Proton-killing Selection to Express Them at the Plasma Membrane