Anisotropic regulation of lateral surface tension directs invagination in C. elegans gastrulation

Epithelial invagination is commonly attributed to actomyosin-driven apical constriction, but how the direction of tissue deformation is determined remains unclear. Here, we show that gastrulation in Caenorhabditis elegans involves anisotropic invagination, with preferential anterior-posterior convergence of neighboring cells. Laser ablation revealed no detectable directional bias in apical cortical recoil, suggesting that anisotropy in apical cortical tension is unlikely to be the primary determinant of the observed directional deformation. Instead, HMR-1/E-cadherin exhibited anisotropic accumulation preferentially at specific lateral cell-cell interfaces, where its enrichment is associated with junctional geometry consistent with reduced interfacial surface tension. Three-dimensional mechanical simulations showed that selectively reducing tension at these interfaces reproduces the observed anisotropic deformation and markedly enhances invagination, whereas uniform tension reduction does not. These findings reveal that spatially patterned lateral surface tension cooperates with apical constriction to control the direction and extent of invagination, uncovering a mechanical role for cell adhesion beyond force transmission.