title: Repetitive intracellular Ca2+ increases at fertilization and the role of Ca2+ in meiosis reinitiation from the first metaphase in oocytes of marine bivalves.
abstract: Spawned oocytes of marine bivalves Limaria hakodatensis, Mytilus edulis, Crassostrea gigas, and Hiatella flaccida are arrested at the first metaphase (metaphase-I) until fertilization. We have measured changes in intracellular Ca2+ ([Ca2+]i) at fertilization in the single oocytes of these bivalves using the fluorescent Ca2+ indicator fura-2. Shortly after insemination, these oocytes displayed a transient [Ca2+]i increase which was usually followed by a period during which [Ca2+]i was kept higher than the resting level (elevated [Ca2+]i period). During this period, [Ca2+]i showed oscillatory increases superimposed on an elevated [Ca2+]i level in Limaria, Crassostrea, and Hiatella, whereas a sustained elevation without pulses occurred in Mytilus. After [Ca2+]i returned to the resting level, repetitive transient [Ca2+]i increases appeared in Limaria, Mytilus, and Hiatella. The [Ca2+]i increases still occurred following external Ca2+ removal shortly after fertilization in all four bivalve species. In contrast, external Ca2+ removal immediately abolished a [Ca2+]i increase induced by excess-K+ seawater in Mytilus. Using another fluorescent Ca2+ indicator, calcium green, we found that during the first transient in Mytilus, [Ca2+]i increased uniformly over the whole oocyte. These results strongly suggest that the fashion of [Ca2+]i increases at fertilization in bivalve oocytes fertilized at metaphase-I differs not only from that in deuterostomes but also from that in protostomes oocytes of which are fertilized at the first prophase.
authors.affiliation: Marine Biological Station of Asamushi, Tohoku University, Aomori, Japan.
authors.forename: R
authors.initials: R
authors.lastname: Deguchi
authors.forename: K
authors.initials: K
authors.lastname: Osanai
mesh_terms: D000818:Animals; D049872:Bivalvia; D002118:Calcium / Q000378:metabolism*; D005306:Fertilization; D008540:Meiosis; D008677:Metaphase; D008974:Mollusca; D009865:Oocytes / Q000378:metabolism*; D012617:Sea Urchins
chemical_list: D002118:Calcium