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.