slc26a3 (dra)-deficient Mice Display Chloride-losing Diarrhea, Enhanced Colonic Proliferation, and Distinct Up-regulation of Ion Transporters in the Colon

Abstract

Mutations in the SLC26A3 (DRA (down-regulated in adenoma)) gene constitute the molecular etiology of congenital chloride-losing diarrhea in humans. To ascertain its role in intestinal physiology, gene targeting was used to prepare mice lacking slc26a3. slc26a3-deficient animals displayed postpartum lethality at low penetrance. Surviving dra-deficient mice exhibited high chloride content diarrhea, volume depletion, and growth retardation. In addition, the large intestinal loops were distended, with colonic mucosa exhibiting an aberrant growth pattern and the colonic crypt proliferative zone being greatly expanded in slc26a3-null mice. Apical membrane chloride/base exchange activity was sharply reduced, and luminal content was more acidic in slc26a3-null mouse colon. The epithelial cells in the colon displayed unique adaptive regulation of ion transporters; NHE3 expression was enhanced in the proximal and distal colon, whereas colonic H,K-ATPase and the epithelial sodium channel showed massive up-regulation in the distal colon. Plasma aldosterone was increased in slc26a3-null mice. We conclude that slc26a3 is the major apical chloride/base exchanger and is essential for the absorption of chloride in the colon. In addition, slc26a3 regulates colonic crypt proliferation. Deletion of slc26a3 results in chloride-rich diarrhea and is associated with compensatory adaptive up-regulation of ion-absorbing transporters. Mutations in the SLC26A3 (DRA (down-regulated in adenoma)) gene constitute the molecular etiology of congenital chloride-losing diarrhea in humans. To ascertain its role in intestinal physiology, gene targeting was used to prepare mice lacking slc26a3. slc26a3-deficient animals displayed postpartum lethality at low penetrance. Surviving dra-deficient mice exhibited high chloride content diarrhea, volume depletion, and growth retardation. In addition, the large intestinal loops were distended, with colonic mucosa exhibiting an aberrant growth pattern and the colonic crypt proliferative zone being greatly expanded in slc26a3-null mice. Apical membrane chloride/base exchange activity was sharply reduced, and luminal content was more acidic in slc26a3-null mouse colon. The epithelial cells in the colon displayed unique adaptive regulation of ion transporters; NHE3 expression was enhanced in the proximal and distal colon, whereas colonic H,K-ATPase and the epithelial sodium channel showed massive up-regulation in the distal colon. Plasma aldosterone was increased in slc26a3-null mice. We conclude that slc26a3 is the major apical chloride/base exchanger and is essential for the absorption of chloride in the colon. In addition, slc26a3 regulates colonic crypt proliferation. Deletion of slc26a3 results in chloride-rich diarrhea and is associated with compensatory adaptive up-regulation of ion-absorbing transporters. The SLC26A3 or DRA (down-regulated in adenoma) gene was originally identified in a subtractive hybridization screen comparing the mRNAs expressed in colon cancer and normal colon tissue (1Schweinfest C.W. Henderson K.W. Suster S. Kondoh N. Papas T.S. Proc. Natl. Acad. Sci. U. S. A. 1993; 90: 4166-4170Crossref PubMed Scopus (193) Google Scholar). DRA is expressed in normal colonic epithelium, but is absent or reduced in adenomas and adenocarcinomas (1Schweinfest C.W. Henderson K.W. Suster S. Kondoh N. Papas T.S. Proc. Natl. Acad. Sci. U. S. A. 1993; 90: 4166-4170Crossref PubMed Scopus (193) Google Scholar). Subsequent studies identified SLC26A3 (DRA) as a member of a large conserved family of anion exchangers (SLC26) that encompass at least 10 distinct genes (2Bissig M. Hagenbuch B. Stieger B. Koller T. Meier P.J. J. Biol. Chem. 1994; 269: 3017-3021Abstract Full Text PDF PubMed Google Scholar, 20Xu J. Henriksnas J. Barone S. Witte D. Shull G.E. Forte J.G. Holm L. Soleimani M. Am. J. Physiol. 2005; 289: C493-C505Crossref PubMed Scopus (103) Google Scholar). Except for SLC26A5 (prestin), all function as anion exchangers with versatility with respect to transported anions (2Bissig M. Hagenbuch B. Stieger B. Koller T. Meier P.J. J. Biol. Chem. 1994; 269: 3017-3021Abstract Full Text PDF PubMed Google Scholar, 20Xu J. Henriksnas J. Barone S. Witte D. Shull G.E. Forte J.G. Holm L. Soleimani M. Am. J. Physiol. 2005; 289: C493-C505Crossref PubMed Scopus (103) Google Scholar). Immunohistochemical studies localized SLC26A3 on the apical membrane of colonic mucosa, with lower levels in the small intestine (4Hoglund P. Haila S. Socha J. Tomaszewski L. Saarialho-Kere U. Karjalainen-Lindsberg M.L. Airola K. de la Holmberg C. Chapelle A. Kere J. Nat. Genet. 1996; 14: 316-319Crossref PubMed Scopus (355) Google Scholar, 25Silberg D.G. Wang W. Moseley R.H. Traber P.G. J. Biol. Chem. 1995; 270: 11897-11902Abstract Full Text Full Text PDF PubMed Scopus (133) Google Scholar). In humans, SLC26A3 encodes a 764-amino acid protein and is located on chromosome 7 in a head-to-tail arrangement with SLC26A4 (pendrin), indicating ancient gene duplication. Genetic analysis studies linked mutations in DRA (SLC26A3) to congenital chloride-losing diarrhea (CLD 5The abbreviations used are: CLD, chloride-losing diarrhea; ES, embryonic stem; ENaC, epithelial sodium channel; KO, knock-out. ; OMIM accession number 214700), a disease manifested by enhanced chloride loss in the stool and volume depletion (4Hoglund P. Haila S. Socha J. Tomaszewski L. Saarialho-Kere U. Karjalainen-Lindsberg M.L. Airola K. de la Holmberg C. Chapelle A. Kere J. Nat. Genet. 1996; 14: 316-319Crossref PubMed Scopus (355) Google Scholar). Functional studies in vitro have demonstrated that SLC26A3 can mediate multiple anion exchange modes, including Cl-/HCO3- , Cl-/oxalate, and Cl-/hydroxyl, and possibly sulfate/hydroxyl exchanges (6Melvin J.E. Park K. Richardson L. Schultheis P.J. Shull G.E. J. Biol. Chem. 1999; 274: 22855-22861Abstract Full Text Full Text PDF PubMed Scopus (253) Google Scholar, 21Greeley T. Shumaker H. Wang Z. Schweinfest C.W. Soleimani M. Am. J. Physiol. 2001; 281: G1301-G1308PubMed Google Scholar, 26Byeon M.K. Frankel A. Papas T.S. Henderson K.W. Schweinfest C.W. Protein Expr. Purif. 1998; 12: 67-74Crossref PubMed Scopus (43) Google Scholar). Similar anion exchange activities have been described previously in apical membranes of the colon (27Rajendran V.M. Binder H.J. Am. J. Physiol. 1999; 276: G132-G137PubMed Google Scholar, 28Tyagi S. Kavilaveettil R.J. Alrefai W.A. Alsafwah S. Ramaswamy K. Dudeja P.K. Exp. Biol. Med. (Maywood). 2001; 226: 912-918Crossref PubMed Google Scholar), the site of abundant DRA expression. To initiate an investigation into the role of DRA in an in vivo model, we created slc26a3 (dra) gene-targeted mice that are null for expression of the slc26a3 gene. This mouse model closely resembles the clinicopathological presentation of human CLD. Functional studies demonstrated that slc26a3-null mice have significantly reduced levels of apical chloride/base exchange activity in the colon and display unique and distinct adaptive regulation of ion transporters in the proximal and distal colon. In addition, the loss of slc26a3 produces an expansion of the proliferative zone of the colonic crypt epithelium, suggesting a role for loss of slc26a3 expression in colon tumor progression. Isolation of Mouse slc26a3 Genomic Clones—A mouse 129S6/SvEv strain genomic library in the vector Lambda Dash II (Stratagene, La Jolla, CA) was screened by plaque hybridization using human DRA cDNA as a probe. A 19-kbp fragment containing at least exons 2-9 was isolated. The identity of the clones was confirmed by Southern blot hybridization and partial sequencing. Targeting Vector Construction—Restriction enzyme mapping revealed the presence of an AgeI restriction site on exon 2 of the mouse dra genomic DNA that was suitable for insertion of the neo cassette. The neo cassette contains the neomycin phosphotransferase gene under the transcriptional control of the RNA polymerase II promoter and the last exon and polyadenylation signal of the hypoxanthine-guanine phosphoribosyltransferase gene for termination. In addition, the neo cassette is flanked by the loxP/Cre recombinase recognition sequences (kindly provided by K. Thomas). The AgeI site of the neo cassette insertion is located 39 bp downstream of the ATG start codon of the dra gene. The targeting vector contains 5.6 kbp of isogenic genomic DNA upstream and 8 kbp of isogenic genomic DNA downstream of the AgeI site. The targeting vector was linearized with SfiI, which cleaves the vector backbone, prior to electroporation into embryonic stem (ES) cells. ES Cell Electroporation—TC1-10 ES cells (kindly provided by Dr. P. Leder) were grown on feeder layers of mouse fibroblasts in knock-out Dulbecco's modified Eagle's medium (Invitrogen) supplemented with 15% serum replacement medium and made complete as described previously (29Hogan B. Costantini F. Lacy E. Manipulating the Mouse Embryo: A Laboratory Manual. Cold Spring Harbor Laboratory, Cold Spring Harbor, NY1986Google Scholar). ES cells (2 × 107) were electroporated with 68 μg of linearized vector using a Bio-Rad Gene Pulser at 600 V and 25 microfarads. Transfected cells were treated with G418 (230 μg/ml) for positive selection. Drug-resistant ES cell clones were expanded and screened for homologous recombination by Southern blot analysis of their genomic DNA (see Fig. 1A). Three of 40 drug-resistant clones were generated and identified by this method. Generation of slc26a3 (dra) Knock-out Mice—The ES cells from three of the positive colonies were microinjected into C57BL/6J blastocysts and implanted in the uteruses of pseudopregnant female mice. Chimeric males that demonstrated significant agouti coat color were mated with BL6 females to generate heterozygotes, which were initially identified by the same Southern blot strategy used to identify targeted ES cell lines. Subsequently, the slc26a3 genotyping was conducted by PCR using two slc26a3 exon 2-specific primers and a primer specific for the RNA polymerase II gene (see below). Genotyping of Mice—Genotyping was performed on tail DNA obtained from mice at weaning and placed directly into 250 μl of lysis buffer (10 mm Tris-HCl (pH 8.5), 50 mm KCl, 1.5 mm MgCl2, 0.01% gelatin, 0.45% Nonidet P-40, and 0.45% Tween 20). PCR was performed with the following primers: mouse slc26a3 exon 2, 5′-GGCAAAATGATCGAAGCCATAGGG-3′ (forward) and 5′-GATGGTCCAGGAATGTCTTGTGATGTC-3′ (reverse); and neo cassette RNA polymerase II, 5′-GGAAGTAGCCGTTATTAGTGGAGAGG-3′ (reverse). The PCR conditions were as follows: 95 °C for 3 min, followed by 32 cycles at 94 °C for 30 s, 55 °C for 30 s, and 72 °C for 30 s. The PCR products were electrophoresed on 3% low melting point agarose (see Fig. 1B) in 45 mm Tris borate and 1 mm (pH and chloride was performed using a obtained from to the stool from the animals were in at and to °C for 30 The were in a and the was and for The sodium was performed by The of the intestinal content was using a of Mouse were and were 10 were in and and in using were and using or to as described Z. S. E. Soleimani M. Am. J. Physiol. PubMed Scopus Google Scholar, 20Xu J. Henriksnas J. Barone S. Witte D. Shull G.E. Forte J.G. Holm L. Soleimani M. Am. J. Physiol. 2005; 289: C493-C505Crossref PubMed Scopus (103) Google Scholar). The used were and RNA Isolation and RNA was from mouse including proximal and distal colon, and to and at RNA were on a agarose containing to by and was performed to W. Proc. Natl. Acad. Sci. U. S. A. PubMed Scopus Google Scholar). The membranes were and to a screen The following DNA were used as specific for for a fragment for a fragment for colonic three PCR products from and and for and and hybridization was performed on from three Immunohistochemical of slc26a3 and in Mouse and mice were with a sodium and the with followed by in sodium buffer (pH were into tissue and in at The were on and were with a and at °C Immunohistochemical was performed as described Z. S. E. Soleimani M. Am. J. Physiol. PubMed Scopus Google using membranes from the proximal colon were by and membranes were with or blot was performed on three from three and of or by luminal membrane from the proximal of three mice and to Z. Wang T. S. B. B. Barone S. U. Soleimani M. Am. J. Physiol. 2005; PubMed Scopus Google Scholar, V.M. Binder H.J. Am. J. Physiol. 1999; 276: G132-G137PubMed Google Scholar, 28Tyagi S. Kavilaveettil R.J. Alrefai W.A. Alsafwah S. Ramaswamy K. Dudeja P.K. Exp. Biol. Med. (Maywood). 2001; 226: 912-918Crossref PubMed Google Scholar), was at in by the P. H. A. C. E. M. Kere J. U. Full Text Full Text PDF PubMed Scopus Google Scholar). The was by The in was by and all were with or and The of mm under three and and with The were 25 mm at and mm at The of 1 mm was under two and was on three and were from and were from The DNA was from was in Z. S. E. Soleimani M. Am. J. Physiol. PubMed Scopus Google Scholar). SLC26A3 were by CA) as described M.K. Henderson K.W. Suster S. Papas T.S. J. J.E. Schweinfest C.W. 1996; 12: Google Scholar). were from are expressed as the analysis was using or analysis of was slc26a3 gene-targeted was generated in ES cells using a targeting vector containing the neo cassette into exon 2 of an isogenic strain dra genomic as in Fig. Three males were generated from dra gene-targeted ES cells and were used to in a analysis of was performed by a PCR using the strategy in Fig. The targeted a PCR whereas the a Fig. a genotyping and knock-out DRA is expressed in a of including small and large and (4Hoglund P. Haila S. Socha J. Tomaszewski L. Saarialho-Kere U. Karjalainen-Lindsberg M.L. Airola K. de la Holmberg C. Chapelle A. Kere J. Nat. Genet. 1996; 14: 316-319Crossref PubMed Scopus (355) Google Scholar, J.E. Park K. Richardson L. Schultheis P.J. Shull G.E. J. Biol. Chem. 1999; 274: 22855-22861Abstract Full Text Full Text PDF PubMed Scopus (253) Google Scholar, M.K. Henderson K.W. Suster S. Papas T.S. J. J.E. Schweinfest C.W. 1996; 12: Google Scholar, S. Saarialho-Kere U. Karjalainen-Lindsberg M.L. H. Airola K. Holmberg C. J. Kere J. P. Cell Biol. PubMed Scopus Google Scholar). the DRA to the (4Hoglund P. Haila S. Socha J. Tomaszewski L. Saarialho-Kere U. Karjalainen-Lindsberg M.L. Airola K. de la Holmberg C. Chapelle A. Kere J. Nat. Genet. 1996; 14: 316-319Crossref PubMed Scopus (355) Google Scholar, J.E. Park K. Richardson L. Schultheis P.J. Shull G.E. J. Biol. Chem. 1999; 274: 22855-22861Abstract Full Text Full Text PDF PubMed Scopus (253) Google Scholar, M.K. Henderson K.W. Suster S. Papas T.S. J. J.E. Schweinfest C.W. 1996; 12: Google Scholar). to for of a null gene we performed blot analysis on from the and of and animals The results showed that the were of DRA expression. was performed to the dra is to the in 1 the results of analysis of at weaning and a of and The from is significant for and suggesting a dra gene on at reduced penetrance. 2 the results of and the demonstrated a that is a significant from of of dra of was as was from an was as The was from an in a of 50 of × of was as was from an was as The was from an in a To dra the of the we the intestinal We have previously that dra gene expression in the at embryonic M.K. Henderson K.W. Suster S. Papas T.S. J. J.E. Schweinfest C.W. 1996; 12: Google Scholar). we at were in the or of the of dra-deficient mice and their normal The for was the suggesting that postpartum lethality is for the Surviving dra-deficient mice exhibited diarrhea with chloride Fig. that the chloride of stool from dra-deficient mice of was significantly that from and animals of In addition, from the dra-deficient mice a content with from their control the were as as described in human CLD. In addition, animals dra-deficient mice were with and animals and greatly of are with the conditions in human CLD, which is by diarrhea with high chloride content and growth in C. PubMed Google Scholar). treated with replacement to have high chloride content diarrhea, but have normal C. PubMed Google Scholar). Mutations in human DRA are the of (4Hoglund P. Haila S. Socha J. Tomaszewski L. Saarialho-Kere U. Karjalainen-Lindsberg M.L. Airola K. de la Holmberg C. Chapelle A. Kere J. Nat. Genet. 1996; 14: 316-319Crossref PubMed Scopus (355) Google Scholar, R.H. P. D.G. de la Haila S. A. Holmberg C. Kere J. Am. J. Physiol. 1999; 276: Google Scholar, S. Saarialho-Kere U. Karjalainen-Lindsberg M.L. H. Airola K. Holmberg C. J. Kere J. P. Cell Biol. PubMed Scopus Google Scholar). the dra-deficient mouse model closely resembles the molecular etiology and of human CLD. and the dra mice from normal dra-deficient mice with of the large with mice The small intestine was in this intestinal is with and postpartum of human and is to increased volume of the C. PubMed Google Scholar). We the of the colonic of that were and with revealed a in dra-deficient mice with in and mice. Fig. an growth pattern of the the crypt were distinct as in normal mucosa This was in from the proximal and distal of but in the Fig. an of that the crypt at the of the which is to the SLC26A3 as a chloride/base exchanger in vitro (6Melvin J.E. Park K. Richardson L. Schultheis P.J. Shull G.E. J. Biol. Chem. 1999; 274: 22855-22861Abstract Full Text Full Text PDF PubMed Scopus (253) Google Scholar, 21Greeley T. Shumaker H. Wang Z. Schweinfest C.W. Soleimani M. Am. J. Physiol. 2001; 281: G1301-G1308PubMed Google Scholar, N. Wang Park M. M. S. P.J. S. J. Physiol. PubMed Scopus Google Scholar). To ascertain the role of SLC26A3 in chloride/base exchange in apical membrane were from the proximal of and slc26a3-null mice and for chloride/base exchange using the method. demonstrated in Fig. the of chloride and Cl-/HCO3- exchange by and in apical membrane from the of slc26a3-null mice The in apical chloride with results from analysis the complete of slc26a3 protein in the of mice and activities of ion transporters in slc26a3 mouse colon. in colonic apical membrane from normal and slc26a3-null mice. analysis of dra in normal and mice. NHE3 expression in normal and slc26a3-null mice. analysis of NHE3 in the of normal and slc26a3 mice. exchanger in colonic apical membrane in normal and slc26a3-null mice. colonic H,K-ATPase expression in normal and slc26a3-null mice. expression of channel in normal and slc26a3-null a the were suggesting an increased of the in slc26a3 mice. To ascertain the molecular of enhanced absorption in the colon, the expression activities of the apical exchanger the sodium and colonic H,K-ATPase were NHE3 expression was increased by and in the proximal and distal from slc26a3-null mice confirmed the up-regulation of NHE3 in the proximal of slc26a3 mice The enhanced expression of NHE3 was associated with increased exchange activity in luminal membrane from the of slc26a3 mice H,K-ATPase is expressed in the distal colon and is for the absorption of H,K-ATPase was increased by in the distal from slc26a3 mice In to NHE3 and colonic an channel is expressed on the apical membranes of the distal colon and is in the absorption of analysis showed significant up-regulation of the and in the distal of slc26a3 mice and of the colonic slc26a3-deficient animals from their normal we the expression for dra and the protein and tumor the cell and In addition, the expression of and and and was of showed expression in all three dra as in Fig. that the mice from the and mice. In normal slc26a3 expression was localized to the apical membrane of the crypt slc26a3 expression was absent in mice dra expression was in a cells into the crypt This is to that for human DRA in normal colon tissue M.K. Henderson K.W. Suster S. Papas T.S. J. J.E. Schweinfest C.W. 1996; 12: Google Scholar, M.K. Henderson K.W. Papas T.S. Schweinfest C.W. 1998; Google Scholar). The proliferative zone in the lower crypt was expanded in dra mice cell and that the expanded zone to of the crypt In normal colon tissue a small number of stem cells that were to the of the This was dra was expressed in the lower crypt the proliferative in normal colon with the expansion of the proliferative A was expressed in more cells in the lower of the crypt with expression in normal colon tissue results that loss of DRA expression the proliferative of the colonic crypt 3 the serum and of function and serum which were for slc26a3-null animals volume depletion with as by increased serum of and sodium and chloride were significantly in slc26a3 mice and aldosterone in a The DRA gene to two as an anion that Cl-/HCO3- exchange in the large intestine (6Melvin J.E. Park K. Richardson L. Schultheis P.J. Shull G.E. J. Biol. Chem. 1999; 274: 22855-22861Abstract Full Text Full Text PDF PubMed Scopus (253) Google Scholar, 21Greeley T. Shumaker H. Wang Z. Schweinfest C.W. Soleimani M. Am. J. Physiol. 2001; 281: G1301-G1308PubMed Google Scholar, N. Wang Park M. M. S. P.J. S. J. Physiol. PubMed Scopus Google and the as a of of epithelial by an M.K. Henderson K.W. Schweinfest C.W. Google Scholar). dra mouse model closely resembles the human disease in clinicopathological including stool chloride diarrhea, and growth retardation. to diarrhea, with as manifested by and slc26a3 mice displayed of as by increased serum aldosterone levels and increased expression of in the increased in slc26a3-null animals with increased a to serum sodium and chloride were in slc26a3 mice of their loss in the colon. results the that of dra the human in mice. We that the mucosa in dra-deficient mice an pattern of This pattern was to the mucosa the crypt a normal was of in the epithelial cells that and from the cell The mucosa of aberrant crypt as in colon Exp. Med. Biol. 1999; PubMed Google Scholar, A. Wang D. PubMed Google or the aberrant crypt in the mouse model of intestinal cancer J. A. S. Google Scholar, J.E. T. E. J. 2001; Google Scholar). the in dra-deficient mice is the of mouse colonic is the cells and into the intestinal M. PubMed Google Scholar). is that the in mice reduced the expanded proliferative zone (see generate more epithelial cells by the of the number of cells. an of cells to the the This is with the The proliferative zone in the colonic of dra-deficient mice was expanded This was confirmed using two of cell and The of this is that loss of dra in increased in the we that human colon cancer cells with human DRA cDNA are M.K. Henderson K.W. Schweinfest C.W. Google Scholar). is that was in the lower of the crypt of the crypt and the epithelium, dra is more In dra model, the cells that dra are to the cell The that this expanded proliferative zone DRA M.K. Henderson K.W. Suster S. Papas T.S. J. J.E. Schweinfest C.W. 1996; 12: Google or low levels of DRA (4Hoglund P. Haila S. Socha J. Tomaszewski L. Saarialho-Kere U. Karjalainen-Lindsberg M.L. Airola K. de la Holmberg C. Chapelle A. Kere J. Nat. Genet. 1996; 14: 316-319Crossref PubMed Scopus (355) Google Scholar, 25Silberg D.G. Wang W. Moseley R.H. Traber P.G. J. Biol. Chem. 1995; 270: 11897-11902Abstract Full Text Full Text PDF PubMed Scopus (133) Google point to the for progression. is that of the from enhanced acid of the exchanger and H,K-ATPase exchange activity to DRA DNA and cell proliferation. In of a of of the exchanger been to DNA in and J. Physiol. PubMed Scopus Google Scholar, A. S. M. M. M. J. 14: PubMed Scopus Google Scholar). Apical and Cl-/HCO3- exchange activities were significantly in the of slc26a3-null mice in increased and of the luminal content in the with that in the stool increased absorption of and in slc26a3-null mouse colon, with compensatory up-regulation of transporters. Three major transporters in the colon are the exchanger ENaC, and colonic which showed up-regulation in slc26a3 mice. The in the apical chloride/base exchange activity and up-regulation of NHE3 and colonic H,K-ATPase the acidic colonic luminal content in dra mice (pH in mice and in mice The in Fig. adaptive the up-regulation of colonic H,K-ATPase and can in enhanced absorption of sodium in the distal colon, with the for sodium absorption This is with the role of colonic H,K-ATPase in the absorption of sodium Z. Shull G.E. Am. J. Physiol. 2001; 281: Google Scholar). The up-regulation of NHE3 in the proximal and distal colon an to the loss of sodium from chloride that SLC26A3 is the major chloride/base exchanger in the colon and that its volume the colonic apical chloride/base exchange activity was sharply reduced in slc26a3 significant activity was in membrane from this the that apical anion exchangers is the small intestinal apical Cl-/HCO3- exchanger which is expressed in the and but is absent in the large intestine Z. S. E. Soleimani M. Am. J. Physiol. PubMed Scopus Google Scholar, Z. Wang T. S. B. B. Barone S. U. Soleimani M. Am. J. Physiol. 2005; PubMed Scopus Google Scholar). We expression of in the of slc26a3 mice a up-regulation of expression was in dra mouse and studies that mice displayed postpartum lethality weaning results that the up-regulation of in the small of dra mice an compensatory role in as and compensatory up-regulation in the of dra mice. In slc26a3 mouse model closely resembles human and produces chloride-rich diarrhea, and distinct adaptive regulation of ion transporters in the colon. In addition, of slc26a3 in the of the colonic crypt in a that a role for DRA in colonic crypt function and We of and Laboratory of for with for with and and of the Gene Targeting and Mouse for in the of gene-targeted mice.