A Novel Mouse Model Reveals a Role for Mitochondria in EarlyLineage Specification and Gastrulation

Mitochondria are increasingly recognized as active regulators of early developmental processes, however, the consequences of mitochondrial dysfunction during mammalian embryogenesis remain poorly understood. In this study, we develop a conditional knock-in mouse model expressing a mitochondrially targeted variant of the bacterial toxin DarT (mitoAtDarT), which induces mitochondrial DNA (mtDNA) damage without affecting the nuclear genome. Ubiquitous expression of mitoAtDarT leads to mitochondrial dysfunction, evidenced by reduced membrane potential and mitochondrial mass, resulting in early embryonic lethality. Employing high-resolution microCT and molecular markers, we demonstrate that mitoAtDarT-expressing embryos fail to undergo normal gastrulation, exhibiting disrupted mesodermal patterning and a complete absence of allantois formation. Surprisingly, defects in lineage specification were evident even earlier, during preimplantation development. Blastocysts expressing mitoAtDarT exhibited reduced total cell numbers, altered trophectoderm-to-inner cell mass ratios, and a striking increase in cells co-expressing lineage markers, indicating a failure in the first cell fate decision. Our findings demonstrate that mitochondrial integrity is essential not only for energy metabolism but also for the precise coordination of cell fate specification and morphogenesis. This work suggests developmental checkpoints are sensitive to mitochondrial genome damage and establishes mitoAtDarT as a powerful tool for dissecting the contributions of mitochondria to embryonic development.