DSL ligands activate the Notch receptor in many cellular contexts across metazoa to specify cell fate. In addition, Notch receptor activity is implicated in post-mitotic morphogenesis and neuronal function. In C. elegans, the DSL family ligand APX-1 is expressed in a subset of cells of the proximal gonad lineage, where it can act as a latent proliferation-promoting signal to maintain proximal germline tumors. Here we examine apx-1 in the proximal gonad and uncover a role in the maintenance of normal ovulation. Depletion of apx-1 causes an endomitotic oocyte (Emo) phenotype and ovulation defects. We find that lag-2 can substitute for apx-1 in this role, that the ovulation defect is partially suppressed by loss of ipp-5, and that lin-12 depletion causes a similar phenotype. In addition, we find that the ovulation defects are often accompanied by a delay of spermathecal distal neck closure after oocyte entry. Although calcium oscillations occur in the spermatheca, calcium signals are abnormal when the distal neck does not close completely. Moreover, oocytes sometimes cannot properly transit through the spermatheca, leading to fragmentation of oocytes once the neck closes. Finally, abnormal oocytes and neck closure defects are seen occasionally when apx-1 or lin-12 activity is reduced in adult animals, suggesting a possible post-developmental role for APX-1 and LIN-12 signaling in ovulation.

Protein kinase A (PKA), which regulates a diverse set of biological functions downstream of cyclic AMP (cAMP), is a tetramer consisting of two catalytic subunits (PKA-C) and two regulatory subunits (PKA-R). When cAMP binds the PKA-R subunits, the PKA-C subunits are released and interact with downstream effectors. In Caenorhabditis elegans (C. elegans), PKA-C and PKA-R are encoded by kin-1 and kin-2, respectively. This review focuses on the contributions of work in C. elegans to our understanding of the many roles of PKA, including contractility and oocyte maturation in the reproductive system, lipid metabolism, physiology, mitochondrial function and lifespan, and a wide variety of behaviors. C. elegans provides a powerful genetic platform for understanding how this kinase can regulate an astounding variety of physiological responses.

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Correct regulation of cell contractility is critical for the function of many biological systems. The reproductive system of the hermaphroditic nematode C. elegans contains a contractile tube of myoepithelial cells known as the spermatheca, which stores sperm and is the site of oocyte fertilization. Regulated contraction of the spermatheca pushes the embryo into the uterus. Cell contractility in the spermatheca is dependent on actin and myosin and is regulated, in part, by Ca 2+ signaling through the phospholipase PLC-1, which mediates Ca 2+ release from the endoplasmic reticulum. Here, we describe a novel role for GSA-1/Gα s, and protein kinase A, composed of the catalytic subunit KIN-1/PKA-C and the regulatory subunit KIN-2/PKA-R, in the regulation of Ca 2+ release and contractility in the C. elegans spermatheca. Without GSA-1/Gα s or KIN-1/PKA-C, Ca 2+ is not released, and oocytes become trapped in the spermatheca. Conversely, when PKA is activated through either a gain of function allele in GSA-1 (GSA-1(GF)) or by depletion of KIN-2/PKA-R, the transit times and total numbers, although not frequencies, of Ca 2+ pulses are increased, and Ca 2+ propagates across the spermatheca even in the absence of oocyte entry. In the spermathecal-uterine valve, loss of GSA-1/Gα s or KIN-1/PKA-C results in sustained, high levels of Ca 2+ and a loss of coordination between the spermathecal bag and sp-ut valve. Additionally, we show that depleting phosphodiesterase PDE-6 levels alters contractility and Ca 2+ dynamics in the spermatheca, and that the GPB-1 and GPB-2 G β subunits play a central role in regulating spermathecal contractility and Ca 2+ signaling. This work identifies a signaling network in which Ca 2+ and cAMP pathways work together to coordinate spermathecal contractions for successful ovulations.

Correct regulation of cell contractility is critical for the function of many biological systems. The reproductive system of the hermaphroditic nematode C. elegans contains a contractile tube of myoepithelial cells known as the spermatheca, which stores sperm and is the site of oocyte fertilization. Regulated contraction of the spermatheca pushes the embryo into the uterus. Cell contractility in the spermatheca is dependent on actin and myosin and is regulated, in part, by Ca 2+ signaling through the phospholipase PLC-1, which mediates Ca 2+ release from the endoplasmic reticulum. Here, we describe a novel role for GSA-1/Gas, and protein kinase A, composed of the catalytic subunit KIN-1/PKA-C and the regulatory subunit KIN-2/PKA-R, in the regulation of Ca 2+ release and contractility in the C. elegans spermatheca. Without GSA-1/Gas or KIN-1/PKA-C, Ca 2+ is not released, and oocytes become trapped in the spermatheca. Conversely, when PKA is activated through either a gain of function allele in GSA-1 (GSA-1(GF)) or by depletion of KIN-2/PKA-R, Ca 2+ is increased, and waves of Ca 2+ travel across the spermatheca even in the absence of oocyte entry. In the spermathecal-uterine valve, loss of GSA-1/Gas or KIN-1/PKA-C results in sustained, high levels of Ca 2+ and a loss of coordination between the spermathecal bag and sp-ut valve. Additionally, we show that depleting phosphodiesterase PDE-6 levels alters contractility and Ca 2+ dynamics in the spermatheca, and that the GPB-1 and GPB-2 Gβ subunits play a central role in regulating spermathecal contractility and Ca 2+ signaling. This work identifies a signaling network in which Ca 2+ and cAMP pathways work together to coordinate spermathecal contractility. Author SummaryOrganisms are full of biological tubes that transport substances such as food, liquids, and air through the body. Moving these substances in a coordinated manner, with the correct directionality, timing, and rate is critical for organism health. In this study we used Caenorhabditis elegans, a small transparent worm, to study how cells in biological tubes coordinate how and when they squeeze and relax. The C. elegans spermatheca is part of the reproductive system, which uses calcium signaling to drive the coordinated contractions that push fertilized eggs out into the uterus. Using genetic analysis and a calcium-sensitive fluorescent protein, we show that the G-protein GSA-1 functions with protein kinase A to regulate calcium release, and contraction of the spermatheca. These findings establish a link between G-protein and cAMP signaling that may apply to similar signaling pathways in other systems.