Lateral cell-cell contact remodeling in the mouse neural plate epithelium

Directed cell neighbor exchange is a universal feature of the morphogenetic flows that shape epithelial tissues during embryonic development. Past experimental and theoretical work on cell rearrangements in polarized epithelial sheets has mainly focused on in-plane neighbor exchanges at apical cell junctions, where active contractile forces are localized. More recent observations have brought to light the active involvement of basolateral domains in cell rearrangements, for instance during convergent extension of the fruit fly germband and mouse neural plate epithelia. How these two sources of subcellular mechanical stress interact and their joint effects on local and global tissue flows are not fully understood. Here, we use detailed three dimensional reconstructions of epithelial cell packings in the early mouse neural plate epithelium to study (1) the motion and lifetimes of vertices and edges where three or more cells meet and provide possible locations of cell rearrangements, and (2) the remodeling dynamics of lateral cell-cell contact surfaces. Together these two measurements provide a comprehensive picture of dynamic changes in cell shapes and cell packing topology during cell rearrangements. We observe a range of persistence times and distinct modes of displacements of high order vertices and edges, and similarly varied persistence times, shapes, and deformation rates in lateral cell-cell contacts, indicative of a rich mechanical microenvironment. We explore how these micro-structural motifs and their time evolution are linked to tissue-scale bending and elongation motions, including using deep clustering methods. Our work provides a basis for linking tissue shape changes to the dynamics of cell-cell contacts in three dimensions in a broad class of epithelial sheets.