Twinfilin modulates tissue contractility through uncapping of capping protein in <i>C. elegans</i>

The actin cytoskeleton is dynamically remodeled by conserved regulators to control cell and tissue mechanics. Although many of these proteins are well studied, their roles in driving tissue-specific contractility remains unclear. Twinfilin, an actin uncapper and depolymerase, has not previously been linked to tissue contractility. Here, we show that the sole twinfilin ortholog in C. elegans, TWF-2, modulates actomyosin contractility in the spermatheca. TWF-2 localizes to the spermathecal cortex through interactions with α-spectrin (SPC-1) and β-spectrin (UNC-70). In vitro, TWF-2 inhibits depolymerization of ADP-actin filaments and modestly promotes depolymerization of ADP-Pi-actin filaments, while also rapidly displacing capping protein (CAP-1 and CAP-2) from filament barbed ends. In vivo, loss of TWF-2 alone does not produce an obvious phenotype, but simultaneous loss of TWF-2 partially rescues the embryonic lethality caused by CAP-1 depletion. Likewise, loss of the contractility regulator SPV-1 results in elevated F-actin and phosphorylated myosin, leading to hypercontractility; this phenotype is suppressed by removing TWF-2, which lowers F-actin levels without affecting myosin or its phosphorylation. These findings demonstrate that TWF-2 modulates actin dynamics in a tissue-specific manner. This work provides the first in vivo evidence that twinfilin modulates contractility and reveals how its interactions with capping protein and spectrins help maintain balanced actomyosin levels in the spermatheca.