Mechanical feedback between a transient core cell and a contractile valve ensures robust organ morphogenesis in C....

Organ morphogenesis requires tightly coordinated changes in cell shape and position, sometimes aided by transient cellular structures. In the C. elegans reproductive system, formation of the spermatheca-uterine valve involves a transient "core cell," but its function has remained unknown. Using long-term live imaging, cell-specific genetic perturbations, and biophysical assays, we show that the core cell mechanically guides valve morphogenesis through two mechanisms: it directs a sliding cell-cell junction that facilitates expansion of the valve's apical domain, and it promotes assembly of a contractile actomyosin network within the valve cell, essential for valve contraction and animal fertility. Ablation or softening of the transient core cell disrupted valve contractility and revealed a mechanical feedback loop in which resistance from the core cell reinforces actomyosin assembly in the valve. Our findings highlight how transient scaffold cells can coordinate morphogenesis in neighboring cells, ensuring precise and robust organ formation.