The myosin light-chain kinase MLCK-1 relocalizes during Caenorhabditis elegans ovulation to promote actomyosin bundle assembly and drive contraction

Productive and coordinated tissue contraction requires spatiotemporal regulation of myosin activity. We use the contractile myoepithelial cells of the Caenorhabditis elegans spermatheca to elucidate the molecular mechanisms involved in contraction. Here, we identify and describe a novel myosin light-chain kinase, MLCK-1, that phosphorylates the myosin regulatory light chain and is required for contraction of the spermatheca and animal fertility. During contraction, MLCK-1 is recruited to basal actomyosin bundles and stabilizes myosin in these bundles downstream of phospholipase PLC-epsilon/PLC-1 and calcium signaling. MLCK and the Rho kinase ROCK are expressed in distinct subsets of spermathecal cells and act in concert to coordinate the timing of contraction. Our results suggest that MLCK-1 phosphorylates myosin primarily in the central bag cells of the spermatheca, while ROCK controls contractility in the distal neck and the valve connecting the spermatheca to the uterus.