Evidence for the involvement of internal calcium stores during serotonin-induced meiosis reinitation in oocytes of the bivalve mollusc Ruditapes philippinarum.
In contrast to the situation found in the bivalves Barnea candida and Spisula solidissima, prophase-arrested oocytes of Ruditapes philippinarum cannot be fertilized when removed from the ovary. They must first undergo germinal vesicle breakdown under the influence of the neurohormone serotonin (5-HT), which drives them to a second block occurring in metaphase of the first maturation division. In the studies described in this paper, we investigate the possibility that calcium is involved as a second messenger in controlling this first step in the reinitiation of meiosis. Our data show that, in addition to 5-HT, ionophore, thapsigargin, and the weak bases ammonia and procaine can also induce prophase-arrested oocytes of Ruditapes to resume meiosis. 5-HT, thapsigargin, and ammonia all trigger a surge of intracellular Ca2+ and are effective even in the absence of external Ca2+. That such Ca2+ transients, which are enhanced in the presence of external Ca2+, actually play a key role in the process of meiosis reinitation is shown by the fact that loading the oocytes with BAPTA/AM or treating them with D-600 blocks maturation. In contrast, excess KCl, which has been shown to trigger meiosis reinitiation of prophase-arrested oocytes of Barnea and Spisula and to activate metaphase I-arrested oocytes of Ruditapes, does not produce any significant intracellular Ca2+ transient nor does it reinitiate meiosis, when added to Ruditapes prophase-arrested oocytes. These data suggest that such voltage-operated Ca2+ channels may only appear during the course of maturation and that both intracellular and extracellular Ca2+ are involved in triggering 5-HT-dependent release from the prophase block in this species.
Guerrier
P
P
Laboratoire de Biologie Moléculaire et Cellulaire, UMR 49, Ecole Normale Supérieure, Lyon, France.
Leclerc-David
C
C
Moreau
M
M
D000818:Animals; D002118:Calcium / Q000502:physiology*; D005260:Female; D008540:Meiosis / Q000187:drug effects*; D008974:Mollusca / Q000502:physiology*; D009865:Oocytes / Q000166:cytology* / Q000187:drug effects; D012701:Serotonin / Q000494:pharmacology*; D015398:Signal Transduction; D013729:Terpenes / Q000494:pharmacology; D019284:Thapsigargin
D013729:Terpenes; D012701:Serotonin; D019284:Thapsigargin; D002118:Calcium