The Caenorhabditis elegans mel-11 myosin phosphatase regulatory subunit affects tissue contraction in the somatic gonad and the embryonic epidermis and genetically interacts with the Rac signaling pathway.

Caenorhabditis elegans embryonic elongation is driven by cell shape changes that cause a contraction of the epidermal cell layer enclosing the embryo. We have previously shown that this process requires a Rho-associated kinase (LET-502) and is opposed by the activity of a myosin phosphatase regulatory subunit (MEL-11). We now extend our characterization and show that mel-11 activity is required both in the epidermis during embryonic elongation and in the spermatheca of the adult somatic gonad. let-502 and mel-11 reporter gene constructs show reciprocal expression patterns in the embryonic epidermis and the spermatheca, and mutations of the two genes have opposite effects in these two tissues. These results are consistent with let-502 and mel-11 mediating tissue contraction and relaxation, respectively. We also find that mel-11 embryonic inviability is genetically enhanced by mutations in a Rac signaling pathway, suggesting that Rac potentiates or acts in parallel with the activity of the myosin phosphatase complex. Since Rho has been implicated in promoting cellular contraction, our results support a mechanism by which epithelial morphogenesis is regulated by the counteracting activities of Rho and Rac. Copyright 1999 Academic Press.