Agenda

While morphogenesis involves the coordinated movements and interactions of neighbouring tissues, the precise role of tissue-tissue interactions in guiding morphogenesis remains largely unknow. Here, we use a minimal model of convergent extension, Xenopus animal cap explants, to uncover how epithelial-mesenchymal coupling guides and facilitates axis elongation. Xenopus embryos and explants have been paramount to our understanding of convergent extension; a key morphogenetic process during embryonic development. While these systems consist of both epithelial and mesenchymal tissues, the prevailing model posits that forces driving convergent extension are primarily generated by the mesenchymal tissues. Here, by combining live imaging, tissue micro-dissection, grafting experiments, and physical modelling, we show that both mesenchymal and epithelial tissues drive axis elongation but in a hierarchical fashion. The epithelial tissue can elongate by itself, while the mesenchymal tissue requires the presence of the epithelium to do so. We also find that epithelial-mesenchymal boundary provides an important spatial cue for setting the axis of elongation; epithelial cells always align parallel to the boundary and consequently as they intercalate, the elongation axis is always perpendicular to the boundary. Altogether the research reveals how tissue boundaries can set the conditions for coherent axis elongation, even in the absence of external patterning cues. More generally, it demonstrates how the coupling between different tissues can guide self-organised morphogenesis.