Transgenic Bax gene efficiently induces lethality in mouse early embryos

Apoptosis is an essential physiological process involved in embryonic development, immune responses, and tissue homeostasis. Despite many studies on pro-apoptotic genes, few reports have directly compared the lethality-inducing potential between them under identical conditions. In this study, we evaluated the lethality-inducing potential of three representative pro-apoptotic genes, Bax , Casp3 , and Casp9 , in mouse early embryos under defined conditions using the doxycycline (Dox)-inducible tetracycline-regulated gene expression system (Tet-On system) in combination with the PiggyBac transposon system. All genes were transcriptionally induced by Dox, and Bax showed the strongest lethal effect, followed by Casp9, while Casp3 did not show any effect. Notably, Bax expression severely impaired blastocyst formation and led to the intense accumulation of the DNA damage marker γH2AX. These findings suggest that introducing upstream apoptotic regulators leads to the more efficient and widespread activation of the apoptotic cascade. Additionally, an unexpected Dox-dependent increase in the expression of reverse tetracycline-controlled transactivator, which is typically driven by a constitutive promoter, was observed, raising the possibility of unanticipated regulatory mechanisms within the Tet-On system. Overall, this study is expected to contribute to a deeper understanding of apoptotic mechanisms and future advancements in regenerative medicine, reproductive engineering, and cancer research.