Mitofusin2 cooperates with Nuage-associated proteins and involves mRNA translational machinery in controlling mRNA fates during spermatogenesis

Mitochondria play a critical role in spermatogenesis and regulated by several mitochondrial fusion proteins. Its interaction with other organelles forms several unique structures, including mitochondria-associated ER membrane (MAM) and a specific type of Nuage close to mitochondria. However, the importance of mitochondria functions and mitochondrial fusion proteins in its associated-structure formation and mRNA translation during spermatogenesis remain unclear. Here, we show that Mitofusin 2 (MFN2), a mitochondrial fusion GTPase protein, cooperates with Nuage-associated proteins, including MIWI, DDX4, TDRKH and GASZ and involves translational machinery to control the fates of gamete-specific mRNAs in spermatogenesis. Conditional mutation of Mfn2 in postnatal germ cells results in male sterility due to germ cell developmental defects characterized by disruption of mitochondrial morphology, abnormal MAMs structure, aberrant mRNA translational processes, and anomalous splicing events. Moreover, MFN2 interacts with MFN1, another mitochondrial fusion protein with high-sequence similar to MFN2, in testes to facilitate spermatogenesis. Mutation of Mfn1 and Mfn2 simultaneously in testes causes very severe infertile phenotypes. Importantly, we further show that MFN2 is enriched in polysome fractions in testes and interacts with MSY2, a germ cell-specific DNA/RNA-binding protein, and eukaryotic elongation factor 1 alpha (eEF1A) to control gamete-specific mRNA translational delay during spermatogenesis. Collectively, our findings demonstrate that MFN2 works with Nuage-associated proteins and involves translational secession to regulate gamete-specific mRNA fates. Our data reveal a novel molecular link among Mitofusins, Nuage-associated proteins, and mRNA translational processes in controlling male germ cell development.