Transient replication of bovine mitochondrial DNA and subsequent placental development in mouse embryos

Mitochondrial DNA (mtDNA) replication during early development is believed to depend on species-specific coordination between the mitochondrial and nuclear genomes. Here, we examined the fate and developmental consequences of bovine mtDNA introduced into mouse embryos using an interspecies mitochondrial transplantation model. Bovine mtDNA exhibited transient amplification during mouse preimplantation development, but declined at the blastocyst stage. Nevertheless, bovine mtDNA persisted in both embryonic and extraembryonic tissues after implantation. Using tetraploid complementation, we further demonstrated that mtB-M embryos developed enlarged placentas with expansion of the spongiotrophoblast layer, accompanied by upregulation of the Sfmbt2-miR-466 m axis. These findings highlight partial engagement of host replication machinery by heterologous mtDNA and species-specific constraints on mtDNA replication in shaping placental development in vivo.