The proximal half of the Drosophila E‐cadherin extracellular region is dispensable for many cadherin‐dependent events but required for ventral furrow formation

The formation of the ventral furrow during Drosophila gastrulation is driven by coordinated apical constriction. Cell-cell adhesion is thought to regulate apical constriction, but the mechanisms are poorly understood. DE-cadherin, an epithelial classic cadherin, has in its membrane-proximal extracellular region a suite of domains absent from vertebrate/urochordate classic cadherins. We constructed DEΔP, a DE-cadherin derivative that lacks the membrane-proximal half of the extracellular region but retains the entire cytoplasmic domain and still exhibits strong cell-cell binding ability. The extracellular region of DEΔP consists of only cadherin repeats, mimicking vertebrate/urochordate classic cadherins. In animals lacking DE-cadherin, DEΔP organized adherens junction assembly and functioned fully in many cadherin-dependent processes, including oogenesis. Embryos in which DE-cadherin was entirely replaced by DEΔP established the blastoderm epithelium but failed to form a ventral furrow. Apical constrictions were initiated relatively normally but subsequently decelerated. These were then followed by catastrophic disruption of the junctional network. Our results suggest that although the membrane-proximal half of the DE-cadherin extracellular region is dispensable for many developmental events, it is essential for efficient and robust apical constriction during ventral furrow formation.