Exon- and contraction-dependent functions of titin in sarcomere assembly.
Titin-truncating variants (TTNtvs) are the major cause of dilated cardiomyopathy (DCM); however, allelic heterogeneity (TTNtvs in different exons) results in variable phenotypes, and remains a major hurdle for disease diagnosis and therapy. Here, we generated a panel of ttn mutants in zebrafish. Four single deletion mutants in ttn.2 or ttn.1 resulted in four phenotypes and three double ttn.2/ttn.1 mutants exhibited more severe phenotypes in somites. Protein analysis identified ttnxu071as a near-null mutant and the other six mutants as hypomorphic alleles. Studies of ttnxu071uncovered a function of titin in guiding the assembly of nascent myofibrils from premyofibrils. By contrast, sarcomeres were assembled in the hypomorphic ttn mutants but either became susceptible to biomechanical stresses such as contraction or degenerated during development. Further genetic studies indicated that the exon usage hypothesis, but not the toxic peptide or the Cronos hypothesis, could account for these exon-dependent effects. In conclusion, we modeled TTNtv allelic heterogeneity during development and paved the way for future studies to decipher allelic heterogeneity in adult DCM.
Department of Biochemistry and Molecular Biology, Division of Cardiovascular Diseases, Mayo Clinic, 200 First St SW, Rochester, MN 55905, USA.
Yu-Huan
YH
Shih
Department of Biochemistry and Molecular Biology, Division of Cardiovascular Diseases, Mayo Clinic, 200 First St SW, Rochester, MN 55905, USA.
Alexey V
AV
Dvornikov
Department of Biochemistry and Molecular Biology, Division of Cardiovascular Diseases, Mayo Clinic, 200 First St SW, Rochester, MN 55905, USA.
Ping
P
Zhu
Department of Biochemistry and Molecular Biology, Division of Cardiovascular Diseases, Mayo Clinic, 200 First St SW, Rochester, MN 55905, USA.|Mayo Graduate School, Mayo Clinic College of Medicine, Rochester, MN 55905, USA.
Xiao
X
Ma
Department of Biochemistry and Molecular Biology, Division of Cardiovascular Diseases, Mayo Clinic, 200 First St SW, Rochester, MN 55905, USA.
Maengjo
M
Kim
Department of Biochemistry and Molecular Biology, Division of Cardiovascular Diseases, Mayo Clinic, 200 First St SW, Rochester, MN 55905, USA.
Yonghe
Y
Ding
Department of Biochemistry and Molecular Biology, Division of Cardiovascular Diseases, Mayo Clinic, 200 First St SW, Rochester, MN 55905, USA xu.xiaolei@mayo.edu.
Xiaolei
0000-0002-4928-3422
X
Xu
D000483:Alleles; D022981:Allelic Imbalance / Q000235:genetics; D000818:Animals; D030801:Animals, Genetically Modified; D002311:Cardiomyopathy, Dilated / Q000235:genetics; D064211:Connectin / Q000235:genetics* / Q000378:metabolism; D009210:Myofibrils / Q000378:metabolism*; D012518:Sarcomeres / Q000235:genetics / Q000378:metabolism*; D017384:Sequence Deletion / Q000235:genetics; D015027:Zebrafish / Q000254:growth & development*
D064211:Connectin
Allelic heterogeneity; Sarcomere assembly; TALEN; Titin; Zebrafish