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First published online August 18, 2003
doi: 10.1242/10.1242/dev.00649

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Metaphase I arrest of starfish oocytes induced via the MAP kinase pathway is released by an increase of intracellular pH

Department of Biology, Ochanomizu University, 2-1-1 Ohtsuka, Bunkyo-ku, Tokyo 112-8610, Japan

^* Author for correspondence (e-mail: kchiba{at}cc.ocha.ac.jp)

Accepted 5 June 2003

Reinitiation of meiosis in oocytes usually occurs as a two-step process during which release from the prophase block is followed by an arrest in metaphase of the first or second meiotic division [metaphase I (MI) or metaphase II (MII)]. The mechanism of MI arrest in meiosis is poorly understood, although it is a widely observed phenomenon in invertebrates. The blockage of fully grown starfish oocytes in prophase of meiosis I is released by the hormone 1-methyladenine. It has been believed that meiosis of starfish oocytes proceeds completely without MI or MII arrest, even when fertilization does not occur. Here we show that MI arrest of starfish oocytes occurs in the ovary after germinal vesicle breakdown. This arrest is maintained both by the Mos/MEK/MAP kinase pathway and the blockage of an increase of intracellular pH in the ovary before spawning. Immediately after spawning into seawater, activation of Na⁺/H⁺ antiporters via a heterotrimeric G protein coupling to a 1-methyladenine receptor in the oocyte leads to an intracellular pH increase that can overcome the MI arrest even in the presence of active MAP kinase.

Key words: MAP kinase, Meiosis, Metaphase arrest, Na⁺/H⁺ antiporter, Starfish

This article has been cited by other articles:

				E. Oita, K. Harada, and K. Chiba Degradation of Polyubiquitinated Cyclin B Is Blocked by the MAPK Pathway at the Metaphase I Arrest in Starfish Oocytes J. Biol. Chem., April 30, 2004; 279(18): 18633 - 18640. [Abstract] [Full Text] [PDF]