Abstract N 7 -methylguanosine (m 7 G) in the variable loop region of tRNA is catalyzed by METTL1/WDR4 heterodimer and stabilizes target tRNA. Here, we reveal essential functions of Mettl1 in Drosophila fertility. Knockout of Mettl1 (Mettl1-KO) lost the elongated spermatids and mature sperm, which was fully rescued by a Mettl1-transgene expression, but not a catalytic-dead Mettl1 transgene. This demonstrates that Mettl1-dependent m 7 G is required for spermatogenesis. Mettl1-KO resulted in a loss of m 7 G modification on a subset of tRNAs and a decreased level of tRNA expression. Strikingly, overexpression of the translational elongation factor, EF1α1, which can compete with the rapid tRNA decay (RTD) pathway in S. cerevisiae , significantly counteracted the sterility of Mettl1-KO males, supporting a critical role of m 7 G modification of tRNAs in spermatogenesis. Ribosome profiling showed that Mettl1-KO led to the ribosome stalling at codons decoded by tRNAs that were reduced in expression. Mettl1-KO also significantly reduced the translation efficiency of genes involved in elongated spermatid formation and sperm stability. These findings reveal a developmental role for m 7 G tRNA modifications and indicate that m 7 G modification-dependent tRNA stability differs among tissues.
