TET exhibits enzymatic-independent and-dependent functions during Drosophila flight muscle development and aging.

BACKGROUND: Enzymes of the Ten-Eleven Translocation family are responsible for 5-methylcytosine (5mC) oxidation and play a key role in regulating DNA demethylation during various developmental processes, including myogenesis. However, they also exhibit 5mC-independent functions whose importance for muscle development remains unexplored. As the Drosophila genome lacks the enzymes required for 5mC deposition but contains a single Tet gene essential for viability, we analyzed its role in flight muscle development. METHODS: Using a combination of genetics, imaging techniques, transcriptomic analysis and functional assays, we assessed the impact of Tet loss of function (using either Tet null or Tet catalytic inactive mutants, as well as Tet knockdown) on indirect flight muscle development from the larval to adult stages and during aging in Drosophila melanogaster. RESULTS: We found that Tet loss leads to a decrease in the number of adult muscle progenitors in the larva, dysregulation of the myogenic expression program in the pupa and disrupted flight muscle organization in the adult. Interestingly, our data reveal that these phenotypes are largely independent of TET enzymatic activity. However, analysis of TET-catalytic inactive flies also highlights the enzyme's critical role in adult fly mobility and its ability to prevent premature muscle aging. Further experiments demonstrate that TET expression in muscle progenitors and the central nervous system is essential for maintaining adult mobility. CONCLUSIONS: These results highlight the crucial role of TET beyond 5mC DNA oxidation, suggesting that both catalytic-dependent and catalytic-independent functions of TET are essential for muscle development and function in vivo.