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Contractile epithelial tubes are found in various organs, such as lung airways and blood capillaries. Their ability to sense luminal pressure and respond with adequate contractility is essential for their physiology, and its mis-regulation results in diseases such as asthma and hypertension. Here, we describe a mechanoresponsive regulatory pathway downstream of tissue stretching that controls contraction of the C. elegans spermatheca, a tubular structure where fertilization occurs. Using live-imaging, we show that ovulation-induced stretching of spermathecal cells leads to recruitment of the RhoGEF RHGF-1 to stress fibers, which activates RHO-1 and myosin II in a positive feedback loop. Through deletion analysis, we identified the PDZ domain of RHGF-1 as responsible for F-actin binding, and genetic epistasis analysis with the RhoGAP spv-1 demonstrated that tension-dependent recruitment of RHGF-1 to F-actin is required for robust spermathecal contractility. Our study illustrates how mechanosensitive regulators of Rho GTPases provide epithelial tubes the ability to tune their contractility in response to internal pressure.

 

Actomyosin-based contractility in smooth muscle and nonmuscle cells is regulated by signaling through the small GTPase Rho and by calcium-activated pathways. We use the myoepithelial cells of the Caenorhabditis elegans spermatheca to study the mechanisms of coordinated myosin activation in vivo. Here, we show that redox signaling modulates RHO-1/Rho activity in this contractile tissue. Exogenously added as well as endogenously generated hydrogen peroxide decreases spermathecal contractility by inhibition of RHO-1, which depends on a conserved cysteine in its nucleotide binding site (C20). Further, we identify an endogenous gradient of H 2 O 2 across the spermathecal tissue, which depends on the activity of cytosolic superoxide dismutase, SOD-1. Collectively, we show that SOD-1-mediated H 2 O 2 production regulates the redox environment and fine tunes Rho activity across the spermatheca through oxidation of RHO-1 C20. 

Cys₂/His₂‐type (C₂H₂) zinc finger proteins, such as ZCT1, are an important class of transcription factors involved in growth, development, and stress responses in plants. In the medicinal plantCatharanthus roseus,the zinc fingerCatharanthustranscription factor (ZCT) family represses monoterpenoid indole alkaloid (MIA) biosynthetic gene expression.Here, we report the analysis of theZCT1promoter, which contains several hormone‐responsive elements.ZCT1is responsive to not only jasmonate, as was previously known, but is also induced by the synthetic auxin, 1‐naphthalene acetic acid (1‐NAA). Through promoter deletion analysis, we show that anactivation sequence‐1‐like (as‐1‐like)‐motif and other motifs contribute significantly toZCT1expression in seedlings. We also show that the activator ORCA3 does not transactivate the expression ofZCT1in seedlings, but ZCT1 represses its own promoter, suggesting a feedback mechanism by which the expression ofZCT1can be limited.