title: Identification of a novel ZIC3 isoform and mutation screening in patients with heterotaxy and congenital heart disease.
abstract: Patients with heterotaxy have characteristic cardiovascular malformations, abnormal arrangement of their visceral organs, and midline patterning defects that result from abnormal left-right patterning during embryogenesis. Loss of function of the transcription factor ZIC3 causes X-linked heterotaxy and isolated congenital heart malformations and represents one of the few known monogenic causes of congenital heart disease. The birth incidence of heterotaxy-spectrum malformations is significantly higher in males, but our previous work indicated that mutations within ZIC3 did not account for the male over-representation. Therefore, cross species comparative sequence alignment was used to identify a putative novel fourth exon, and the existence of a novel alternatively spliced transcript was confirmed by amplification from murine embryonic RNA and subsequent sequencing. This transcript, termed Zic3-B, encompasses exons 1, 2, and 4 whereas Zic3-A encompasses exons 1, 2, and 3. The resulting protein isoforms are 466 and 456 amino acid residues respectively, sharing the first 407 residues. Importantly, the last two amino acids in the fifth zinc finger DNA binding domain are altered in the Zic3-B isoform, indicating a potential functional difference that was further evaluated by expression, subcellular localization, and transactivation analyses. The temporo-spatial expression pattern of Zic3-B overlaps with Zic3-A in vivo, and both isoforms are localized to the nucleus in vitro. Both isoforms can transcriptionally activate a Gli binding site reporter, but only ZIC3-A synergistically activates upon co-transfection with Gli3, suggesting that the isoforms are functionally distinct. Screening 109 familial and sporadic male heterotaxy cases did not identify pathogenic mutations in the newly identified fourth exon and larger studies are necessary to establish the importance of the novel isoform in human disease.
authors.affiliation: Department of Pediatrics, Cincinnati Children's Hospital Medical Center and University of Cincinnati College of Medicine, Cincinnati, Ohio, United States of America.
authors.forename: James E J
authors.initials: JE
authors.lastname: Bedard
authors.forename: Allison M
authors.initials: AM
authors.lastname: Haaning
authors.forename: Stephanie M
authors.initials: SM
authors.lastname: Ware
mesh_terms: D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D003914:Dextrocardia / Q000175:diagnosis / Q000235:genetics* / Q000378:metabolism; D005091:Exons / Q000235:genetics; D005260:Female; D020869:Gene Expression Profiling; D040181:Genetic Diseases, X-Linked / Q000175:diagnosis / Q000235:genetics* / Q000378:metabolism; D005820:Genetic Testing; D006367:HeLa Cells; D059446:Heterotaxy Syndrome / Q000175:diagnosis / Q000235:genetics* / Q000378:metabolism; D018398:Homeodomain Proteins / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008969:Molecular Sequence Data; D009154:Mutation; D041681:NIH 3T3 Cells; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid; D012689:Sequence Homology, Nucleic Acid; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism; D016335:Zinc Fingers / Q000235:genetics
chemical_list: D018398:Homeodomain Proteins; D020033:Protein Isoforms; D014157:Transcription Factors; C491595:ZIC3 protein, human; C491594:Zic3 protein, mouse