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Cardiac troponin T is essential in sarcomere assembly and cardiac contractility

Nature Genetics volume 31, pages 106–110 (2002)Cite this article

Abstract

Mutations of the gene (TNNT2) encoding the thin-filament contractile protein cardiac troponin T are responsible for 15% of all cases of familial hypertrophic cardiomyopathy, the leading cause of sudden death in young athletes1,2. Mutant proteins are thought to act through a dominant-negative mode that impairs function of heart muscle3. TNNT2 mutations can also lead to dilated cardiomyopathy, a leading cause of heart failure4. Despite the importance of cardiac troponin T in human disease, its loss-of-function phenotype has not been described. We show that the zebrafish silent heart (sih) mutation affects the gene tnnt2. We characterize two mutated alleles of sih that severely reduce tnnt2 expression: one affects mRNA splicing, and the other affects gene transcription. Tnnt2, together with α-tropomyosin (Tpma) and cardiac troponins C and I (Tnni3), forms a calcium-sensitive regulatory complex within sarcomeres5. Unexpectedly, in addition to loss of Tnnt2 expression in sih mutant hearts, we observed a significant reduction in Tpma and Tnni3, and consequently, severe sarcomere defects. This interdependence of thin-filament protein expression led us to postulate that some mutations in tnnt2 may trigger misregulation of thin-filament protein expression, resulting in sarcomere loss and myocyte disarray, the life-threatening hallmarks of TNNT2 mutations in mice and humans6,7.

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Figure 1: sih phenotype.
Figure 2: sih mutant cardiomyocytes show normal cellular excitation, but have defective sarcomere assembly.
Figure 3: Reduced protein expression of Tpma, Tnnt2 and Tnni3 in sih mutant hearts.
Figure 4: Severely reduced tnnt2 mRNA expression in sih mutant embryos throughout development.
Figure 5: sih encodes Tnnt2.
Figure 6: The sihb109 promoter deletion abolishes reporter expression in vivo.

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Acknowledgements

We thank A. Navarro and S. Waldron for their dedicated care of our fish, K. MacDonald for his expertise in generating electron micrographs, and M. Brook and F. Aburto for their assistance with the Quicktime movies. We thank C. Kimmel, F. Stockdale, J. Potter, P. Anderson and R. Breitbart for sharing valuable reagents; W. Tidyman, C. Ordahl and B. Black for helpful discussions about cardiac gene regulation and P. Wolters, M. Zeiger, R. Reijo-Pera and members of the Stainier lab for their comments on this manuscript. A.S. was supported as a March of Dimes fellow of the Pediatric Scientist Development Program and by the American Heart Association Western States Affiliate. This work was supported in part by grants from the National Institutes of Health (to A.S., M.C.F. and D.Y.R.S., and to Charles Kimmel supporting the mutagenesis screen), as well as grants from the Packard Foundation and the American Heart Association (to D.Y.R.S.).

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Authors and Affiliations

  1. Department of Biochemistry and Biophysics, Programs in Developmental Biology, Genetics and Human Genetics, University of California at San Francisco, 513 Parnassus Avenue, Box 0448, San Francisco, 94143-0448, California, USA

    Amy J. Sehnert, Anja Huq & Didier Y. R. Stainier

  2. Department of Pediatrics, University of California at San Francisco, California, USA

    Amy J. Sehnert

  3. Laboratory of Molecular Genetics, National Institute of Child Health & Human Development, National Institutes of Health, Bethesda, Maryland, USA

    Brant M. Weinstein

  4. Institute of Neuroscience, University of Oregon, Eugene, Oregon, USA

    Charline Walker

  5. Cardiovascular Research Center, Massachusetts General Hospital, Boston, Massachusetts, USA

    Mark Fishman

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  1. Amy J. Sehnert
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Correspondence to Didier Y. R. Stainier.

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Sehnert, A., Huq, A., Weinstein, B. et al. Cardiac troponin T is essential in sarcomere assembly and cardiac contractility. Nat Genet 31, 106–110 (2002). https://doi.org/10.1038/ng875

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