An internal promoter underlies the difference in disease severity between N- and C-terminal truncation mutations of Titin in zebrafish.
Jun ZouDiana TranMai BaalbakiLing Fung TangAnnie PoonAngelo PeloneroErron W TitusChristiana YuanChenxu ShiShruthi PatchavaElizabeth HalperJasmine GargIrina MovsesyanChaoying YinRoland WuLisa D WilsbacherJiandong LiuRonald L HagerShaun R CoughlinMartin JinekClive R PullingerJohn P KaneDaniel O HartPui-Yan KwokRahul C DeoPublished in: eLife (2015)
Truncating mutations in the giant sarcomeric protein Titin result in dilated cardiomyopathy and skeletal myopathy. The most severely affected dilated cardiomyopathy patients harbor Titin truncations in the C-terminal two-thirds of the protein, suggesting that mutation position might influence disease mechanism. Using CRISPR/Cas9 technology, we generated six zebrafish lines with Titin truncations in the N-terminal and C-terminal regions. Although all exons were constitutive, C-terminal mutations caused severe myopathy whereas N-terminal mutations demonstrated mild phenotypes. Surprisingly, neither mutation type acted as a dominant negative. Instead, we found a conserved internal promoter at the precise position where divergence in disease severity occurs, with the resulting protein product partially rescuing N-terminal truncations. In addition to its clinical implications, our work may shed light on a long-standing mystery regarding the architecture of the sarcomere.