  During embryonic development, regeneration and homeostasis, cells have to
physically integrate into their target tissues, where they ultimately execute
their function. Despite a significant body of research on how mechanical forces
instruct cellular behaviors within the plane of an epithelium, very little is
known about the mechanical interplay at the interface between migrating cells
and their surrounding tissue, which has its own dynamics, architecture and
identity. Here, using quantitative in vivo imaging and molecular perturbations,
together with a theoretical model, we reveal that multiciliated cell (MCC)
precursors in the Xenopus embryo form dynamic filopodia that pull at the
vertices of the overlying epithelial sheet to probe their stiffness and
identify the preferred positions for their integration into the tissue.
Moreover, we report a novel function for a structural component of vertices,
the lipolysis-stimulated lipoprotein receptor (LSR), in filopodia dynamics and
show its critical role in cell intercalation. Remarkably, we find that pulling
forces equip the MCCs to remodel the epithelial junctions of the neighboring
tissue, enabling them to generate a permissive environment for their
integration. Our findings reveal the intricate physical crosstalk at the
cell-tissue interface and uncover previously unknown functions for mechanical
forces in orchestrating cell integration.
