title: Self-incompatibility response induced by calcium increase in sperm of the ascidian Ciona intestinalis.
abstract: Many hermaphroditic organisms possess a self-incompatibility system to avoid self-fertilization. Recently, we identified the genes responsible for self-sterility in a hermaphroditic primitive chordate (ascidian), Ciona intestinalis: sperm-side polycystin 1-like receptors s-Themis-A/B and egg-side fibrinogen-like ligands on the vitelline coat (VC) v-Themis-A/B. Here, we investigated the sperm behavior and intracellular Ca(2+) concentration ([Ca(2+)](i)) in response to self/nonself-recognition. We found that sperm motility markedly decreased within 5 min after attachment to the VC of self-eggs but not after attachment to the VC of nonself-eggs and that the apparent decrease in sperm motility was suppressed in low Ca(2+) seawater. High-speed video analysis revealed that sperm detached from the self-VC or stopped motility within 5 min after binding to the self-VC. Because s-Themis-B contains a cation channel domain in its C terminus, we monitored sperm [Ca(2+)](i) by real-time [Ca(2+)](i) imaging using Fluo-8H-AM (AAT Bioquest, Inc.). Interestingly, we found that sperm [Ca(2+)](i) rapidly and dramatically increased and was maintained at a high level in the head and flagellar regions when sperm interacted with the self-VC but not when the sperm interacted with the nonself-VC. The increase in [Ca(2+)](i) was also suppressed by low-Ca(2+) seawater. These results indicate that the sperm self-recognition signal triggers [Ca(2+)](i) increase and/or Ca(2+) influx, which elicits a self-incompatibility response to reject self-fertilization in C. intestinalis.
authors.affiliation: Sugashima Marine Biological Laboratory, Graduate School of Science,  Nagoya University, Toba, Mie 517-0004,  Japan.
authors.forename: Takako
authors.initials: T
authors.lastname: Saito
authors.forename: Kogiku
authors.initials: K
authors.lastname: Shiba
authors.forename: Kazuo
authors.initials: K
authors.lastname: Inaba
authors.forename: Lixy
authors.initials: L
authors.lastname: Yamada
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Sawada
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling; D002938:Ciona intestinalis / Q000502:physiology*; D008297:Male; D008954:Models, Biological; D010063:Ovum / Q000166:cytology / Q000378:metabolism; D012399:Rotation; D057945:Self-Fertilization / Q000502:physiology*; D013081:Sperm Motility; D013094:Spermatozoa / Q000378:metabolism*; D014817:Vitelline Membrane / Q000378:metabolism
chemical_list: D002118:Calcium