Reciprocal interactions between EMT and BMP signalling drive collective cell invasion.

During collective cell invasion, epithelial-to-mesenchymal transition (EMT) and morphogen signalling-mediated cell fate specification are traditionally viewed as a linear cascade: morphogens drive cell fates that activate EMT programs. Here, we uncover reciprocal coupling between EMT initiation and BMP signalling mediated by SNAI2 and SMAD1. Using substrate-induced EMT in ex vivo explants, we demonstrate that EMT initiation upregulates SMAD1 expression, priming cells for BMP signalling competence across germ layers. Single-cell RNA sequencing reveals SNAI2 and SMAD1 co-expression in EMT initiation regions, and SNAI2 overexpression is sufficient to induce ectopic SMAD1 expression in vivo. While BMP signalling is dispensable for EMT initiation, it regulates cell fate proportions, dispersal dynamics, precursor region depletion rates, and migration directionality. This coupling provides a mechanism for synchronising cell fate specification with invasion progression during axis elongation, positioning EMT as a process that actively modulates morphogen competence to coordinate tissue-level cell behaviours during collective cell invasion. HighlightsO_LIEMT initiation directly primes BMP pathway competence. C_LIO_LISNAI2 overexpression is sufficient to drive ectopic SMAD1 expression. C_LIO_LIBMP signalling is spatiotemporally restricted to EMT initiation zones. C_LIO_LIBMP signalling tunes cell fate proportions and invasion dynamics. C_LI O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=132 SRC="FIGDIR/small/691808v1_ufig1.gif" ALT="Figure 1"> View larger version (64K): org.highwire.dtl.DTLVardef@1ae1e78org.highwire.dtl.DTLVardef@526260org.highwire.dtl.DTLVardef@b892f1org.highwire.dtl.DTLVardef@1b74815_HPS_FORMAT_FIGEXP M_FIG C_FIG