Depletion of Zebrafish Titin Reduces Cardiac Contractility by Disrupting the Assembly of Z-Discs and A-Bands

Seeley, M., Huang, W., Chen, Z., Wolff, W.O., Lin, X., and Xu, X.
Circulation research   100(2): 238-245 (Journal)
Registered Authors
Chen, Zhenyue, Huang, Wei, Lin, Xueying, Seeley, Michael, Xu, Xiaolei
zebrafish, sarcomere, genetics, cardiac muscle
MeSH Terms
  • Alternative Splicing/genetics
  • Animals
  • Connectin
  • Muscle Proteins/biosynthesis
  • Muscle Proteins/deficiency*
  • Muscle Proteins/genetics*
  • Muscle Proteins/metabolism
  • Myocardial Contraction/genetics*
  • Myocardial Contraction/physiology
  • Protein Isoforms/deficiency
  • Protein Isoforms/genetics
  • Protein Isoforms/metabolism
  • Protein Isoforms/physiology
  • Protein Kinases/biosynthesis
  • Protein Kinases/deficiency*
  • Protein Kinases/genetics*
  • Protein Kinases/metabolism
  • Protein Processing, Post-Translational/genetics*
  • Sarcomeres/metabolism
  • Zebrafish
  • Zebrafish Proteins/deficiency*
  • Zebrafish Proteins/genetics*
  • Zebrafish Proteins/metabolism
  • Zebrafish Proteins/physiology
17170364 Full text @ Circ. Res.
The genetic study of titin has been notoriously difficult because of its size and complicated alternative splicing routes. Here, we have used zebrafish as an animal model to investigate the functions of individual titin isoforms. We identified 2 titin orthologs in zebrafish, ttna and ttnb, and annotated the full-length genomic sequences for both genes. We found that ttna, but not ttnb, is required for sarcomere assembly in the heart as well as the subsequent establishment of cardiac contractility. In fact, ttna is the earliest sarcomeric mRNA that is expressed in the heart, which makes it an early molecular marker for cardiomyocyte differentiation. Surprisingly, ttna is required for later steps of sarcomere assembly, including the assembly of Z-discs and A-bands, but not for early steps such as the assembly of Z-bodies and nonstriated myosin filaments. Reduction of individual titin isoforms in vivo using morpholino-modified antisense oligonucleotides indicated that (1) both N2B exon-containing and N2A exon-containing isoforms of ttna are required for sarcomere assembly in the heart; (2) N2A exon-containing isoforms of both ttna and ttnb are required for sarcomere assembly in the somites; and (3) the N2B exon-containing isoforms of ttnb are expressed later than other titin isoforms and are probably involved in modulating their expression; however, these isoforms of ttnb are not required for sarcomere assembly. Collectively, our results reveal distinct functions of different titin isoforms and suggest that various phenotypes in "titinopathies" may be attributable to the disruption of different titin isoforms.
Genes / Markers
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Mutations / Transgenics
Human Disease / Model
Sequence Targeting Reagents
Engineered Foreign Genes