Gastrula‐Premarked Posterior Enhancer Primes Posterior Tissue Development Through Cross‐Talk with TGF‐β Signaling Pathway

The regulatory mechanisms governing cell fate determination, particularly lineage diversification during mammalian embryonic development, remain poorly understood with in‐depth regulatory paradigms yet to be fully elucidated. Here, leveraging the epigenetic landscape of mouse gastrula, p‐Enh is identified, an enhancer located within the first intron of Cdx2 and epigenetically pre‐marked in the primitive streak region, as a pivotal regulator for posterior tissue development in mouse embryos. Morphological and single‐cell transcriptomic analyses confirmed embryonic lethality phenotype with disrupted posterior tissue development trajectories in p‐Enh‐KO embryos. Molecularly, apart from regulating the neighboring coding‐gene Cdx2 in cis , the findings suggest that p‐Enh also modulates the global transcriptome and epigenomic landscape, which might through the transient production of eRNA in trans . Further investigation revealed p‐Enh‐derived eRNAs participate in the regulatory cascades of TGF‐β signaling by directly interacting with SMAD4 protein. Combinatorial modulation of TGF‐β signaling and p‐Enh‐eRNA abundance can largely rescue the posterior development deficiency in in vitro gastruloids through a Cdx2 ‐independent mechanism. Thus, a potential model is proposed in which the broadly distributed p‐Enh transcripts within the nucleus can serve as essential cross‐modular coordinators, priming the posterior development of mouse embryo.