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 (1). DRA is expressed in normal colonic epithelium, but is absent or reduced in adenomas and adenocarcinomas (1). Subsequent studies identified SLC26A3 (DRA) as a member of a large conserved family of anion exchangers (SLC26) that encompass at least 10 distinct genes (2-20). Except for SLC26A5 (prestin), all function as anion exchangers with versatility with respect to transported anions (2-20). Immunohistochemical studies localized SLC26A3 on the apical membrane of colonic mucosa, with lower levels in the small intestine (4, 25). 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 5 ; OMIM accession number 214700), a disease manifested by enhanced chloride loss in the stool and volume depletion (4). Functional studies in vitro have demonstrated that SLC26A3 can mediate multiple anion exchange modes, including Cl Ϫ /HCO 3 Ϫ , Cl Ϫ /oxalate, and Cl Ϫ /hydroxyl, and possibly sulfate/hydroxyl exchanges (6, 21-26). Similar anion exchange activities have been described previously in apical membranes of the colon (27, 28), 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 slc2...

A cDNA, which we call DRA (for downregulated in adenoma) has been isolated.

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Ets1 is a member of the Ets transcription factor family. Alternative splicing of exon VII results in two naturally occurring protein isoforms: full-length Ets1 (p51-Ets1) and Ets1⌬VII (p42-Ets1). These isoforms bear key distinctions regarding protein-protein interactions, DNA binding kinetics, and transcriptional target specificity. Disruption of both Ets1 isoforms in mice results in the loss of detectable NK and NKT cell activity and defects in B and T lymphocytes. We generated mice that express only the Ets1 ⌬VII isoform. Ets1⌬VII homozygous mice express no p51-Ets1 and elevated levels of the p42-Ets1 protein relative to the wild type and display increased perinatal lethality, thymomegaly, and peripheral lymphopenia. Proliferation was increased in both the thymus and the spleen, while apoptosis was decreased in the thymus and increased in the spleen of homozygotes. Significant elevations of CD8 ؉ and CD8 ؉ CD4 ؉ thymocytes were observed. Lymphoid cell (CD19 ؉ , CD4 ؉ , and CD8 ؉ ) reductions were predominantly responsible for diminished spleen cellularity, with fewer memory cells and a failure of homeostatic proliferation to maintain peripheral lymphocytes. Collectively, the Ets1⌬VII mutants demonstrate lymphocyte maturation defects associated with misregulation of p16 Ink4a , p27Kip1 , and CD44. Thus, a balance in the differential regulation of Ets1 isoforms represents a potential mechanism in the control of lymphoid maturation and homeostasis.