title: Mutually exclusive and cassette exons underlie alternatively spliced isoforms of the Na/Ca exchanger.
abstract: We have analyzed the gene structure that gives rise to tissue-specific isoforms of the Na/Ca exchanger. Five distinct isoforms of the Na/Ca exchanger from rabbit brain, kidney, and heart have been identified previously to which we now add a new brain isoform. Reverse-transcribed polymerase chain reaction, library screening, and sequence analysis of cDNA coding regions indicate that the only significant alteration of the Na/Ca exchanger cDNA in rabbit brain, kidney, and heart isoforms is located in the carboxyl end of the putative intracellular loop of the protein, a region recently linked to ionic and metabolic regulation of the Na/Ca exchanger. Additionally, we find that the Na/Ca exchanger isoforms found in lung and skeletal muscle may arise from among these same six isoforms. Examination of the gene structure of the Na/Ca exchanger in rabbit indicates how the single gene that encodes for the Na/Ca exchanger is alternatively spliced to give rise to the five rabbit isoforms. Specifically, sequence analysis of the intron-exon boundaries reveals the presence of two "mutually exclusive" exons in conjunction with four "cassette" exons in the region of the Na/Ca exchanger gene that codes for the carboxyl end of the predicted intracellular loop region. This unusual arrangement of exons in the Na/Ca exchanger gene could allow for the generation of up to 32 different Na/Ca exchanger mRNAs and accounts for the isoforms identified to date.
authors.affiliation: Department of Pharmacology and Experimental Therapeutics, University of Maryland School of Medicine, Baltimore 21201.
authors.forename: P
authors.initials: P
authors.lastname: Kofuji
authors.forename: W J
authors.initials: WJ
authors.lastname: Lederer
authors.forename: D H
authors.initials: DH
authors.lastname: Schulze
mesh_terms: D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001921:Brain / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D002352:Carrier Proteins / Q000096:biosynthesis* / Q000235:genetics; D004247:DNA / Q000737:chemistry / Q000378:metabolism; D017931:DNA Primers; D018076:DNA, Complementary / Q000737:chemistry / Q000378:metabolism; D005091:Exons; D014644:Genetic Variation; D015698:Genomic Library; D007438:Introns; D007668:Kidney / Q000378:metabolism; D008969:Molecular Sequence Data; D009206:Myocardium / Q000378:metabolism; D009928:Organ Specificity; D016133:Polymerase Chain Reaction; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000096:biosynthesis*; D011817:Rabbits; D017386:Sequence Homology, Amino Acid; D012964:Sodium / Q000378:metabolism; D019831:Sodium-Calcium Exchanger
chemical_list: D002352:Carrier Proteins; D017931:DNA Primers; D018076:DNA, Complementary; D012333:RNA, Messenger; D019831:Sodium-Calcium Exchanger; D004247:DNA; D012964:Sodium; D002118:Calcium