title: FBN1 isoform expression varies in a tissue and development-specific fashion.
abstract: Mutations in FBN1 cause Marfan syndrome, a heritable disorder of connective tissue. FBN1 encodes the extracellular matrix protein, fibrillin. Our objective was to elucidate the extent that variation in RNA splicing contributes to FBN1 isoforms. To identify FBN1 splice variants, we scanned each of its 64 internal exons in a set of pooled human brain cDNA samples. FBN1 splicing is generally efficient as we identified only two variants. Neither variant has previously been reported in the literature and include (i) an isoform which contains a cryptic 105 basepair exon between exons 54 and 55 (54A-FBN1) and (ii) an isoform which contains a cryptic 62 basepair exon between exons 57 and 58 (57A-FBN1). We compared 57A-FBN1 and FBN1 expression in multiple human tissues, including adult skeletal muscle and brain, as well as fetal skeletal muscle, brain, liver, aorta, lung, skin, and heart. 57A-FBN1 represents 8-44% of FBN1 mRNA and varies in a tissue- and development-specific fashion. In adult brain, 57A-FBN1 represented 39±3 (%, mean±SD) of total FBN1 expression. In contrast, 57A-FBN1 represented 19±2 (%, mean±SD) of FBN1 expression in skeletal muscle. In fetal tissue, the 57A-FBN1 proportion was highest in brain (27%) and low elsewhere, e.g., skin, aorta and lung (9-13%). In summary, a significant proportion of FBN1 is expressed as 57A-FBN1 and this proportion varies in a tissue- and development-specific fashion. Since the 57A insertion creates a premature stop codon that mimics Marfan-associated mutations, the protein encoded by 57A-FBN1 is likely to not be functional. These results suggest that altered splicing may modulate disease severity, regulate FBN1 expression, and potentially represent a therapeutic target.
authors: University of Kentucky College of Medicine, University of Kentucky, Lexington, KY, USA. mary.burchett@uky.edu
authors: Mary E
authors: ME
authors: Burchett
authors: I-Fang
authors: IF
authors: Ling
authors: Steven
authors: S
authors: Estus
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000595:Amino Acid Sequence; D001921:Brain / Q000378:metabolism; D005091:Exons; D000071838:Fibrillin-1; D000071837:Fibrillins; D006801:Humans; D007668:Kidney / Q000378:metabolism; D008099:Liver / Q000378:metabolism; D008168:Lung / Q000378:metabolism; D008382:Marfan Syndrome / Q000235:genetics* / Q000378:metabolism*; D008840:Microfilament Proteins / Q000235:genetics* / Q000378:metabolism*; D008875:Middle Aged; D008969:Molecular Sequence Data; D018482:Muscle, Skeletal / Q000378:metabolism; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D012326:RNA Splicing; D055815:Young Adult; D054392:Adipokines
chemical_list: D000071838:Fibrillin-1; D000071837:Fibrillins; D008840:Microfilament Proteins; D020033:Protein Isoforms; C000605722:FBN1 protein, human; D054392:Adipokines