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Regulation of actomyosin contractility

Contractile tubes are a hallmark of many important animal organs, such as blood and lymphatic vessels, lung airways, mammary and salivary glands, and urinal and reproductive tracts. In larger tubular tissues, contractility is afforded by smooth muscle cells surrounding epithelial cells, and in smaller tubes the epithelial or endothelial cells themselves are contractile. Misregulation of contractility, and hence of tube diameter, is responsible for several human diseases, such as hypertension and asthma. Mechanical cues, sensed by cell adhesion sites and the cytoskeleton, play an important role in regulating cellular contractility. However, the role of such mechanosensing in regulating contractility of biological tubes in vivo remains unknown. The C. elegans spermatheca, part of the nematode reproductive system, where sperm are stored and fertilization takes place, is a contractile tubular tissue. Spermathecal cells exhibit features of smooth muscle cells and the entire tissue is readily accessible to genetic manipulation and in vivo imaging. Importantly, misregulation of spermathecal contractility has deleterious consequences for fertility. Previous work has shown that Ca2+ signaling plays an important role in spermathecal contraction and the squeezing of embryos into the uterus after fertilization. More recently, we have shown that activity of the small GTPase RHO-1 is essential for spermathecal contraction by activation of actomyosin, a part of the cytoskeleton. However, how these two pathways work together and what molecular mechanisms determine the activation of RHO-1 at the right place and time are still poorly understood. We are using C. elegans spermatheca as a highly tractable model of a smooth muscle-like tubular tissue to uncover novel signaling pathways controlling actomyosin contractility. We are particularly investigating, using tissue-specific knockdown methods and imaging by spinning disk confocal microscopy, the upstream regulators of RHO-1 signaling, RhoGEFs and RhoGAPs, and the effect of calcium signaling on RHO-1 activity. In addition, we are also examining the involvement of microtubules in spermatheca contraction. Taken together, this data will help us understand the signaling process that leads to spermatheca contraction, testing the hypothesis that spermathecal stretching by oocyte entry has a role in this signaling pathway. This knowledge may help design future strategies for the treatment of human diseases caused by misregulation of tubular contractility.

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