Tmx2 Maintains Mitochondrial Function to Support Preimplantation Embryogenesis.

Thioredoxin (TRX)-related transmembrane proteins (TMX), a subgroup of the protein disulfide isomerase (PDI) family, comprise a class of transmembrane proteins with diverse biological functions. Among these, TMX2 (PDIA12) remains one of the least characterized members. Recent studies have identified missense mutations in TMX2 associated with aberrant brain development and cerebellar malformations, highlighting its potential importance in developmental processes. Notably, Tmx2 mutant embryos exhibit developmental arrest at the E3.5 stage, suggesting a critical role in preimplantation embryogenesis. However, the precise molecular and cellular functions of Tmx2 in mammalian embryonic development remain largely unexplored. In this study, we provide novel insights into the essential role of Tmx2 during preimplantation embryonic development in mice. We demonstrate that TMX2 is specifically expressed in mouse embryos, with its subcellular localization closely associated with mitochondria during the two-cell to eight-cell stages. Knockdown of Tmx2 recapitulates the phenotypic defects observed in genetic mutants, revealing a pronounced impairment in blastomere proliferation, as confirmed by EdU incorporation assays. Furthermore, TUNEL assays indicate a significant increase in apoptotic signaling in Tmx2-deficient embryos, accompanied by elevated mRNA levels of the cell cycle inhibitors p21 and p53. Mechanistically, we show that Tmx2 knockdown disrupts mitochondrial function, leading to oxidative stress and impaired mitophagy and autophagy in developing embryos. These findings suggest that Tmx2 plays a pivotal role in maintaining mitochondrial integrity and cellular homeostasis during preimplantation embryogenesis. In summary, our study elucidates the critical role of Tmx2 in preimplantation embryonic development in mice, primarily through its regulation of mitochondrial function. These results advance our understanding of the molecular mechanisms governing preimplantation embryonic development and establish Tmx2 as a key regulator of mitochondrial dynamics and cellular survival during this critical developmental window.