Arrest at Metaphase of Meiosis I in Starfish Oocytes in the Ovary is Maintained by High CO2 and Low O-2 Concentrations in Extracellular Fluid

作者：Moriwaki Kei; Nakagawa Takako; Nakaya Fumio; Hirohashi Noritaka; Chiba Kazuyoshi^*

来源：Zoological Science, 2013, 30(11): 975-984.

DOI：10.2108/zsj.30.975

• meiosis
• oocyte
• metaphase arrest
• starfish
• CO2

During the spawning process in starfish, oocytes are arrested at metaphase of meiosis I (MI) within the ovary, and reinitiate meiosis only after they have been released into the seawater. However, this arrest does not occur if the ovary is removed from the animal. As the pH of the coelomic fluid is buffered by CO2/H+/HCO3-, we investigated the involvement of gas concentrations in MI arrest. In vivo, the CO2 level in the coelomic fluid was high (similar to 1.5% vs. 0.04% in air) and the O-2 level was low (0.1-1.0% vs. similar to 20% in air). When these gas conditions were reproduced in isolated coelomic fluid or seawater, ovarian oocytes arrested at MI, just as in vivo. Isolated oocytes from the ovary required the similar high CO2 and low O-2 level to remain arrested in MI and had an intracellular pH of similar to 6.9. Intracellular pH increased to similar to 7.3 when oocytes were transferred to seawater equilibrated with air, a condition that mimics that of spawning. We used ammonium acetate to clamp intracellular pH at different levels and found that MI arrest occurred when intracellular pH was similar to 6.9. Our results support the idea that high CO2 and low O-2 in the ovarian environment lead to low intracellular pH and MI arrest, while spawning into the seawater with low CO2 and high O-2 results in high intracellular pH and release from MI arrest. The biological significance of MI arrest is that oocytes are spawned into seawater at the optimal physiological state of MI when the least polyspermy occurs.

• 出版日期2013-11