The spermatheca is a 24-cell tube in the middle of the C. elegans reproductive system that functions as the site of fertilization, undergoing rounds of extreme stretch to accommodate entering oocytes followed by contraction to expel the fertilized egg. The contractility of the spermatheca is tightly regulated at the actomyosin level by calcium signaling and Rho activity. Many smooth muscle and non-muscle systems in other animals also exhibit actomyosin contractility regulated by calcium signaling and Rho activity, making the spermatheca a powerful model to study fundamental biological mechanisms regulating contractile tubes. SPV-1, a RhoGAP with an F-BAR domain, has emerged as a key regulator of contractility in the spermatheca. When
spv-1 is lost, the spermatheca contracts immediately upon oocyte entry, leading to faster egg transit and perturbed egg shapes. Calcium signaling has been shown to drive contraction in the spermatheca, so we used the genetically encoded calcium sensor GCaMP expressed in the cells of the spermatheca to determine if the loss of
spv-1 alters calcium signaling. Using widefield fluorescence microscopy, we monitored calcium activity in the spermatheca during ovulation events. We find that the loss of
spv-1 results in a more rapid onset of calcium signaling upon oocyte entry, and elevated calcium levels throughout ovulation events. Overexpressing
spv-1::mApple results in the expected opposite calcium phenotype, with slower onset of calcium signaling upon oocyte entry and decreased calcium levels throughout ovulation events. In addition to altered calcium levels, mutants with altered levels of
spv-1 also lack proper spatiotemporal regulation of calcium signaling. High levels of SPV-1 result in retention of the embryo in the spermatheca, and preliminary data suggests that SPV-1 acts in a dose dependent manner to regulate the baseline calcium level. Studies using a mutated
spv-1 which lacks RhoGAP activity exhibit calcium signaling similar to the loss of
spv-1, suggesting that
spv-1 controls calcium signaling primarily through GTPase activity. Previous work established that contractility of the spermatheca is carefully regulated by calcium signaling and RhoA activity. This work suggests that there is significant crosstalk between these two regulatory networks. Ongoing work aims to identify effectors that SPV-1 uses to regulate calcium signaling, and to use quantitative microscopy and analysis to more deeply understand how SPV-1 is modulating calcium signaling.