shi, w. | bioRxiv Science

bioRxiv2026

β-Catenin Drives Apical-Basal Polarization to facilitate TE lineage commitment In Vitro and In Vivo

Embryo polarization is critical for the first cell fate segregation. While mechanisms underlying its initiation have been described, the intrinsic signaling pathways that regulate this process remain poorly understood. Here, we show that mouse embryonic stem cells, when aggregated under defined conditions, recapitulate the first lineage segregation to generate trophectoderm (TE)-like cell populations and undergo self-organized morphogenesis into blastocyst-like structures. In the blastoid-forming medium, we identify CHIR99021 is essential for the generation of blastoids from both ESCs and totipotent-like cells. CHIR99021 promotes cell polarization and TE differentiation by activating the WNT/{beta}-catenin pathway and upregulating associated genes. Consistent with this, genetic ablation of {beta}-catenin abolished the cell polarization and disrupted blastoid formation from ESCs, a defect that was restored by {beta}-catenin overexpression. Moreover, {beta}-catenin depletion compromised cell polarization in natural embryos. Collectively, this study establishes the Wnt/{beta}-catenin as a critical regulator initiating polarization in vitro and in mouse early embryo development.

developmental biology↗

bioRxiv2026

A Phospho-Switch for Cell Fate Control

Cell fate control is thought to be complex, likely involving both cell intrinsic and extrinsic factors, and remains ill-defined at the molecular level. Here we show a phospho-switch controls cell fate both in vitro and in vivo. We first show that SALL4 is phosphorylated at multiple sites, but only T903 as the primary one as SALL4T903A lost BAF interaction and [~]90% activity in reprogramming. Mechanistically, we demonstrate that SALL4pT903 is sensitive to BMP4 signaling through DUSP9 axis. Finally, we show by tetraploid embryo complementation that mESCs harboring SALL4T903A can sustain embryo development but with severe defects including cranial hypoplasia and flattened skull vault after birth. A genome wide search identifies 608 transcription factors harboring the same HTG motif sandwiched by two zinc fingers, suggesting that this phospho-switch may be a conserved mechanism to control cell fate. In briefA phosphorylation switch, pT903, in SALL4 governs cell fate by modulating BAF complex interaction in response to BMP4-DUSP9 signaling, as its dephosphorylation abrogates reprogramming and causes cranial defects in mice, suggesting that such switches may broadly regulate cell fate machinery. HighlightsO_LIA T903 phospho-switch in SALL4 gates BAF interaction to orchestrate gene activation and reprogramming C_LIO_LIBMP4-DUSP9 signaling converges on SALL4pT903 dephosphorylation to couple extracellular cues with cell fate determination C_LIO_LIDisrupting the SALL4-T903 phospho-switch causes severe postnatal developmental defects in mice. C_LIO_LIThe HTGE motif may function as a central switch on key transcription factors for sensing upstream signals C_LI

developmental biology↗