Variant AE2 Anion Exchanger Transcripts Accumulate in Multiple Cell Types in the Chicken Gastric Epithelium

Abstract

Molecular analyses have resulted in the isolation of two chicken stomach AE2 anion exchanger cDNAs, AE2-1 and AE2-2. The ϳ4.3-kilobase (kb) AE2-1 cDNA contains an open reading frame that encodes a predicted polypeptide of ϳ135 kDa that is homologous to AE2 anion exchangers from other species. The partial ϳ1.7-kb AE2-2 cDNA, which differs from the AE2-1 cDNA in two regions, would be predicted to encode an AE2 polypeptide with an alternative N-terminal cytoplasmic tail. Examination of the distribution of these variant transcripts has revealed that AE2 transcripts ranging in size from ϳ4.4 to ϳ7.3 kb accumulate in various adult tissues. However, in the stomach, the unique sequence at the 5-end of AE2-1 is preferentially associated with transcripts that range in size from ϳ4.5 to ϳ4.9 kb, while the unique sequence at the 5-end of AE2-2 is preferentially associated with the ϳ7.3-kb AE2 RNA species. In situ hybridization analyses have further revealed that AE2 transcripts accumulate to very high levels within the acid-secreting epithelial cells of the profound gland in the stomach and, to a lesser extent, within the mucussecreting cells of the superficial gland that line the stomach lumen. This result suggests that AE2 anion exchangers are involved in the regulation of intracellular pH in each of these gastric epithelial cell types.Plasma membrane electroneutral anion exchangers are involved in the regulation of intracellular pH (1) and cell volume (2). The best characterized anion exchanger is the erythroid AE1 anion exchanger (band 3 protein), which primarily mediates the one-for-one exchange of bicarbonate for chloride (3). Molecular studies have indicated that variant AE1 anion exchangers are encoded by the AE1 gene in mouse (4), rat (5), human (6), and chicken (7-9). These variant AE1 transcripts differ only at their 5Ј-ends and encode polypeptides with alternative N-terminal cytoplasmic domains. These molecular analyses coupled with immunolocalization studies (10, 11) have suggested that specific AE1 variants mediate the electroneutral anion exchange activity that has been localized to the basolateral membrane of the acid-secreting A-intercalated cells of the kidney collecting duct.Electroneutral anion exchange activities have also been characterized in a variety of other cell types, including gastric parietal cells (12), cardiac Purkinje fibers (13), and renal mesangial cells (14,15). The genes that encode most of these anion exchange activities are not known. However, immunolocalization studies using AE2 anion exchanger-specific peptide antibodies have suggested that the AE2 anion exchanger mediates the basolateral chloride/bicarbonate exchange activity of the acid-secreting parietal cells of the mammalian stomach (16). The studies described here have revealed that variant chicken AE2 anion exchanger transcripts are generated by a complex pattern of alternative transcriptional initiation and differential RNA splicing. These transcripts are expressed in a wide variety of tissues including the proventriculus, th...

Primary Structure of a Sperm Cell Anion Exchanger and its Messenger Ribonucleic Acid Expression During Spermatogenesis

“…AE1 (previously termed band 3) is a founding member of the sodium-independent Cl Ϫ /HCO 3 Ϫ -exchanger gene family, which according to the current knowledge consists of at least two additional members, namely AE2 and AE3 [13][14][15][16][17][18]. In addition, each gene produces tissue-specific variants by means of alternative splicing and/or by the use of alternative promoters [19][20][21][22]. AE1 is found in erythrocytes, kidney, and heart [18,19,23].…”

“…AE1 is found in erythrocytes, kidney, and heart [18,19,23]. AE2 is found in almost all tissues, but mainly in the stomach, kidney, and intestine [21,24,25]. AE3 is expressed predominantly in the brain and heart [17,26].…”

Cell type-specific and developmentally regulated expression of the AE1 anion exchanger in the chicken chorioallantoic membrane

“…4). Secondly, tissue sections from the stomach, which expresses the AE2 anion exchanger at high levels (Cox et al 1996), were also negative for staining with the AE1 antiserum (Fig. 5).…”

“…12B). The fact that the sequence between amino acids 185-203 of AE1-1b is not conserved in the AE2 (Cox et al 1996) and AE3 (Kudrycki et al 1990) anion exchangers strongly suggests that the multiple species observed in the CAM are all derived from the AE1 gene. Whether the multiple species observed in the CAM are the result of differential glycosylation of a single AE1 variant or are derived from multiple variant AE1 transcripts awaits further analysis.…”

“…AE2 is widely expressed in nonerythroid tissues including the stomach, kidney, liver, pancreas, salivary glands and male reproductive system (Jons et al 1994;Brosius et al 1995;Cox et al 1996;Garcìa et al 1998;Stuart-Tilley et al 1998;Holappa et al 1999;Jensen et al 1999;Castillo et al 2000;Roussa 2001). AE3 is primarily expressed in the nervous system, cardiac muscle and gut (Kudrycki et al 1990;Linn et al 1992Linn et al , 1995Yannoukakos et al 1994).…”