guanine nucleotides in the meiotic maturation of starfish oocytes regulation of the actin cytoskeleton and of ca2+ signaling鸟嘌呤核苷酸海星卵母细胞的减数分裂成熟调节肌动蛋白细胞骨架和ca2 +的信号.pdfVIP

Guanine Nucleotides in the Meiotic Maturation of Starfish Oocytes: Regulation of the Actin Cytoskeleton and of Ca2+ Signaling 1 2 2 2 2 Keiichiro Kyozuka , Jong T. Chun , Agostina Puppo , Gianni Gragnaniello , Ezio Garante , Luigia Santella2* 1 Research Center for Marine Biology, Tohoku University, Asamushi, Japan, 2 Stazione Zoologica Anton Dohrn, Napoli, Italy Abstract Background: Starfish oocytes are arrested at the first prophase of meiosis until they are stimulated by 1-methyladenine (1- MA). The two most immediate responses to the maturation-inducing hormone are the quick release of intracellular Ca2+ and the accelerated changes of the actin cytoskeleton in the cortex. Compared with the later events of oocyte maturation such as germinal vesicle breakdown, the molecular mechanisms underlying the early events involving Ca2+ signaling and actin changes are poorly understood. Herein, we have studied the roles of G-proteins in the early stage of meiotic maturation. Methodology/Principal Findings: By microinjecting starfish oocytes with nonhydrolyzable nucleotides that stabilize either active (GTPcS) or inactive (GDPbS) forms of G-proteins, we have demonstrated that: i) GTPcS induces Ca2+ release that mimics the effect of 1-MA; ii) GDPbS completely blocks 1-MA-induced Ca2+; iii) GDPbS has little effect on the amplitude of the Ca2+ peak, but significantly expedites the initial Ca2+ waves induced by InsP3 photoactivation, iv) GDPbS induces unexpectedly striking modification of the cortical actin networks, suggesting a link between the cytoskeletal change and the modulation of the Ca2+ release kinetics; v) alteration of cortical actin networks with jasplakinolide, GDPbS, or actinase E, all led