Mettl1-dependent m7G tRNA modification is essential for maintaining fertility and proper spermatogenesis in Drosophila melanogaster
N7-methylguanosine (m7G) in variable loop region of tRNA stabilizes target tRNA expression, which is catalyzed by METTL1/WDR4 heterodimer. Here, we unveil essential functions of Mettl1 in Drosophila fertility. Mettl1-knockout (Mettl1-KO) decreases elongated spermatid and mature sperm, which is fully rescued by Mettl1-transgene expression, but not catalytic dead Mettl1-transgene, demonstrating that Mettl1-dependent m7G is required for spermatogenesis. Mettl1-KO shows loss of m7G modification on subset of tRNAs and decreased level of tRNA expression. Strikingly, overexpression of translational elongation factor EF1a that can compete with rapid tRNA decay (RTD) pathway in S. cerevisiae, significantly counteract the sterility in Mettl1-KO male, supporting a critical role of m7G tRNA modification in spermatogenesis. Ribo-seq analysis shows that Mettl1-KO elevates ribosome collisions at codons decoded by reduced tRNAs and significantly reduces translation of genes involved in elongated spermatid formation and sperm stability.  These findings reveal a developmental role for m7G tRNA modifications and suggest that m7G ??modification-dependent tRNA stability differs among tissues. Overall design: Ribosome profiling and RNA-Seq of testis of fly