PDK1 is required for the hormonal signaling pathway leading to meiotic resumption in starfish oocytes |
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Authors: | Hiraoka Daisaku Hori-Oshima Sawako Fukuhara Takeshi Tachibana Kazunori Okumura Eiichi Kishimoto Takeo |
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Institution: | Laboratory of Cell and Developmental Biology, Graduate School of Bioscience, Tokyo Institute of Technology, Nagatsuta, Midoriku, Yokohama 226-8501, Japan. |
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Abstract: | Meiotic resumption is generally under the control of an extracellular maturation-inducing hormone. It is equivalent to the G2-M phase transition in somatic cell mitosis and is regulated by cyclin B-Cdc2 kinase. However, the complete signaling pathway from the hormone to cyclin B-Cdc2 is yet unclear in any organism. A model system to analyze meiotic resumption is the starfish oocyte, in which Akt/protein kinase B (PKB) plays a key mediator in hormonal signaling that leads to cyclin B-Cdc2 activation. Here we show in starfish oocytes that when PDK1 activity is inhibited by a neutralizing antibody, maturation-inducing hormone fails to induce cyclin B-Cdc2 activation at the meiotic G2-M phase transition, even though PDK2 activity becomes detectable. These observations assign a novel role to PDK1 for a hormonal signaling intermediate toward meiotic resumption. They further support that PDK2 is a molecule distinct from PDK1 and Akt, and that PDK2 activity is not sufficient for the full activation of Akt in the absence of PDK1 activity. |
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Keywords: | Akt/PKB Cell cycle Cyclin B-Cdc2 G2-M phase transition Hormonal signaling Meiotic resumption Oocyte maturation PDK1/2 Starfish oocytes |
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