title: Soluble sperm extract specifically recapitulates the initial phase of the Ca2+ response in the fertilized oocyte of P. occelata following a G-protein/ PLCβ signaling pathway.
abstract: Matured oocytes of the annelidan worm Pseudopotamilla occelata are fertilized at the first metaphase of the meiotic division. During the activation by fertilizing spermatozoa, the mature oocyte shows a two-step intracellular Ca2+ increase. Whereas the first Ca2+ increase is localized and appears to utilize the inositol 1,4,5-trisphosphate (IP3)-sensitive Ca2+ stores, the second Ca2+ increase is global and involves Ca2+ influx via voltage-gated Ca2+ channels on the entire surface of the oocyte. To study how sperm trigger the Ca2+ increases during fertilization, we prepared soluble sperm extract (SE) and examined its ability to induce Ca2+ increases in the oocyte. The SE could evoke a Ca2+ increase in the oocyte when it was added to the medium, but not when it was delivered by microinjection. However, the second-step Ca2+ increase leading to the resumption of meiosis did not follow in these eggs. Local application of SE induced a non-propagating Ca2+ increase and formed a cytoplasmic protrusion that was similar to that created by the fertilizing sperm at the first stage of the Ca2+ response, important for sperm incorporation into the oocyte. Our results suggest that the fertilizing spermatozoon may trigger the first-step Ca2+ increase before it fuses with the oocyte in a pathway that involves the G-protein-coupled receptor and phospholipase C. Thus, the first phase of the Ca2+ response in the fertilized egg of this species is independent of the second phase of the Ca2+ increase for egg activation.
authors.affiliation: Research Center for Marine Biology,Graduate School of Life Sciences,Tohoku University,Asamushi,Aomori,039-3501,Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Nakano
authors.affiliation: Research Center for Marine Biology,Graduate School of Life Sciences,Tohoku University,Asamushi,Aomori,039-3501,Japan.
authors.forename: Keiichiro
authors.initials: K
authors.lastname: Kyozuka
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002457:Cell Extracts / Q000737:chemistry / Q000494:pharmacology*; D004625:Embryo, Nonmammalian / Q000187:drug effects / Q000378:metabolism; D004963:Estrenes / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000378:metabolism; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D008297:Male; D008845:Microinjections; D009865:Oocytes / Q000187:drug effects / Q000502:physiology; D011077:Polychaeta / Q000196:embryology / Q000378:metabolism; D011760:Pyrrolidinones / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects; D012995:Solubility; D013084:Sperm-Ovum Interactions; D013094:Spermatozoa / Q000737:chemistry*; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors / Q000378:metabolism; D015053:Zygote / Q000187:drug effects / Q000378:metabolism*
chemical_list: D002457:Cell Extracts; D004963:Estrenes; D011760:Pyrrolidinones; C060229:1-(6-((3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D010738:Type C Phospholipases; D019204:GTP-Binding Proteins; D002118:Calcium
keywords: 4; 5-trisphosphate (IP3); Annelida oocyte; Ca2+ function; Ca2+ increase; Egg activation; Inositol 1; Sperm extract