title: A novel cryptic exon identified in the 3' region of intron 2 of the human dystrophin gene.
abstract: The dystrophin gene, which is mutated in Duchenne muscular dystrophy (DMD), is the largest known human gene and is characterized by the huge size of its introns. Intron 2, the second largest intron, is 170-kb long and has been shown to include a 140-bp cryptic exon (exon 2a) in its 5' region. The rest of this intron has no known function. In this study, we find that another cryptic exon, located in the 3' region of intron 2, is activated in a promoter- or tissue-specific manner. An unknown 98-bp insertion precisely between exons 2 and 3 was identified in one of the dystrophin mRNAs from lymphocytes of a DMD patient with a duplication of exon 2. This 98-bp sequence, located in the 3' region of intron 2, was found to possess a branch point, acceptor and donor splice-site consensus sequences, and an exonic splicing enhancer sequence, and thus is a novel exon, which we named "exon 2b." In lymphocytes, exon 2b incorporation was detected in the muscle-specific, promoter-driven transcript. Five of 20 normal human tissue mRNAs, including cardiac and skeletal muscle mRNAs, were confirmed to contain a fragment extending from exon 1 to exon 2b by reverse transcription PCR amplification, indicating that exon 2b is activated in a tissue-specific manner. This provides a clue to a novel cause of dystrophinopathy.
authors.affiliation: Department of Pediatrics, Kobe University Graduate School of Medicine, 7-5-1 Kusunokicho, Chuo, Kobe, 650-0017, Japan.
authors.forename: Van Khanh
authors.initials: VK
authors.lastname: Tran
authors.affiliation: Department of Pediatrics, Kobe University Graduate School of Medicine, 7-5-1 Kusunokicho, Chuo, Kobe, 650-0017, Japan.
authors.forename: Zhujun
authors.initials: Z
authors.lastname: Zhang
authors.affiliation: Department of Pediatrics, Kobe University Graduate School of Medicine, 7-5-1 Kusunokicho, Chuo, Kobe, 650-0017, Japan.
authors.forename: Mariko
authors.initials: M
authors.lastname: Yagi
authors.affiliation: Department of Pediatrics, Kobe University Graduate School of Medicine, 7-5-1 Kusunokicho, Chuo, Kobe, 650-0017, Japan.
authors.forename: Atsushi
authors.initials: A
authors.lastname: Nishiyama
authors.affiliation: Department of Pediatrics, Kobe University Graduate School of Medicine, 7-5-1 Kusunokicho, Chuo, Kobe, 650-0017, Japan.
authors.forename: Yasuaki
authors.initials: Y
authors.lastname: Habara
authors.affiliation: Department of Pediatrics, Kobe University Graduate School of Medicine, 7-5-1 Kusunokicho, Chuo, Kobe, 650-0017, Japan.
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Takeshima
authors.affiliation: Department of Pediatrics, Kobe University Graduate School of Medicine, 7-5-1 Kusunokicho, Chuo, Kobe, 650-0017, Japan. matsuo@kobe-u.ac.jp.
authors.forename: Masafumi
authors.initials: M
authors.lastname: Matsuo
mesh_terms: D020413:3' Untranslated Regions; D017398:Alternative Splicing; D001483:Base Sequence; D002675:Child, Preschool; D016384:Consensus Sequence; D017124:Conserved Sequence; D004247:DNA / Q000097:blood; D016189:Dystrophin / Q000235:genetics*; D005091:Exons; D006801:Humans; D007438:Introns; D007564:Japan; D008214:Lymphocytes / Q000378:metabolism; D008297:Male; D008969:Molecular Sequence Data; D021141:Nucleic Acid Amplification Techniques; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic; D022821:RNA Splice Sites; D012333:RNA, Messenger / Q000032:analysis / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D014158:Transcription, Genetic
chemical_list: D020413:3' Untranslated Regions; D016189:Dystrophin; D022821:RNA Splice Sites; D012333:RNA, Messenger; D004247:DNA