PES-8, a ZP-like protein, is required for cytoskeletal organization and contractility in the Caenorhabditis elegans spermatheca.

Proper regulation of contraction and relaxation in biological tubes is essential for organismal function. In Caenorhabditis elegans, the spermatheca, composed of smooth muscle-like cells, undergoes repeated stretching and contraction as oocytes pass through. Here we describe PES-8, a previously uncharacterized protein, as a regulator of spermathecal contractility. PES-8 contains a predicted extracellular zona pellucida-like domain and an unstructured cytoplasmic tail, suggesting dual roles in extracellular and cytoplasmic signaling. PES-8 localizes to the plasma membrane of the spermatheca, the spermathecal-uterine valve, and the uterus. Functional analysis shows that PES-8 is essential for spermathecal function; its loss disrupts actomyosin fiber alignment, FLN-1/filamin localization, apical junction organization, and Ca²⁺ signaling, preventing oocyte transit. These findings identify PES-8 as a key regulator of cytoskeletal organization and calcium-mediated contractility in the C. elegans spermatheca.