Disruption of mitochondrial integrity impairs early lineage specification and embryonic development in the novel conditional MitoAtDarT mouse model

Mitochondria are increasingly recognised as regulators of developmental state, but how mitochondrial dysfunction influences lineage transitions during mammalian embryogenesis remains poorly understood. Here, we generate a conditional mouse model expressing a mitochondrially targeted, attenuated variant of the DNA ADP-ribosyltransferase DarT (mitoAtDarT). Early activation of mitoAtDarT reduced mitochondrial membrane potential and mitochondrial area, altered mitochondrial morphology, and caused embryonic lethality, without detectable increases in nuclear {gamma}H2AX. Developmental defects were evident before implantation: mitoAtDarT expressing blastocysts contained fewer cells and an increased proportion of CDX2/SOX2 double-positive cells, consistent with delayed or incomplete resolution of trophectoderm and inner-cell-mass identities. Following implantation, embryos showed progressive growth retardation and reduced proliferation without widespread apoptosis. By E7.5, Brachyury-positive posterior mesoderm was retained and expanded despite failure of allantoic morphogenesis, while broad SOX2- and SOX17-positive compartments remained recognisable. These defects were accompanied by increased PKM2 expression. Together, our findings suggest that mitochondrial dysfunction can compromise the resolution and progression of developmental states. The conditional mitoAtDarT model provides a means to determine whether mitochondrial state represents a general requirement for lineage transitions or whether particular developmental programmes are selectively vulnerable.