Background: In C. elegans, a sperm-sensing mechanism regulates oocyte meiotic maturation and ovulation, tightly coordinating sperm availability and embryo production; sperm release the major sperm protein (MSP) signal to trigger meiotic resumption. Meiotic arrest depends on the parallel function of the oocyte VAB-1 MSP/Eph receptor and somatic G protein signaling. MSP promotes meiotic maturation by antagonizing Eph receptor signaling and counteracting inhibitory inputs from the gonadal sheath cells. Results: Here, we present evidence suggesting that in the absence of the MSP ligand, the VAB-1 Eph receptor inhibits meiotic maturation while either in or in transit to the endocytic-recycling compartment. VAB-1::GFP localization to the RAB-11-positive endocytic-recycling compartment is independent of ephrins but is antagonized by MSP signaling. Two negative regulators of oocyte meiotic maturation, DAB-1/Disabled and RAN-1, interact with the VAB-1 receptor and are required for its accumulation in the endocytic-recycling compartment in the absence of MSP or sperm (hereafter referred to as MSP/sperm). Inactivation of the endosomal recycling regulators rme-1 or rab-11.1 causes a vab-1-dependent reduction in the meiotic-maturation rate in the presence of MSP/sperm. Further, we show that Gαs signaling in the gonadal sheath cells, which is required for meiotic maturation in the presence of MSP/sperm, affects VAB-1::GFP trafficking in oocytes. Conclusions: Regulated endocytic trafficking of the VAB-1 MSP/Eph receptor contributes to the control of oocyte meiotic maturation in C. elegans. Eph receptor trafficking in other systems may be influenced by the conserved proteins DAB-1/Disabled and RAN-1 and by crosstalk with G protein signaling in neighboring cells.
Bibliographical noteFunding Information:
We are grateful to the Caenorhabditis Genetics Center, Anjon Audhya, Andrew Chisholm, Jonathan Cooper, Andy Fire, Barth Grant, Ethan Lee, Michael Miller, Karen Oegema, Geraldine Seydoux, and Ann Spang for providing strains and reagents. Thanks to Lingzhi Ma and Tom Hayes for help with microscopy. Min Ni generously shared his biolistic transformation apparatus. We thank Amy Ham for assistance with mass spectrometry. Sean Conner, Barth Grant, Bob Herman, Priah Nadarajan, Caroline Spike, Todd Starich, Meg Titus, and John Yochem provided many useful suggestions. This work was supported by NIH grants GM65115 and GM57173 to D.G.