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Vol. 19, Issue 8, 3544-3553, August 2008

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Live Observation of Forespore Membrane Formation in Fission Yeast

Taro Nakamura^*, Haruhiko Asakawa^,, Yukiko Nakase^*,, Jun Kashiwazaki^*, Yasushi Hiraoka^,, and Chikashi Shimoda^*

*Department of Biology, Graduate School of Science, Osaka City University, Osaka 558-8585, Japan; Kobe Advanced ICT Research Center, National Institute of Information and Communications Technology, Kobe 651-2492, Japan; and Graduate School of Frontier Biosciences, Osaka University, Suita 565-0871, Japan

Submitted April 23, 2008; Revised May 29, 2008; Accepted June 4, 2008
Monitoring Editor: Fred Chang

Sporulation in the fission yeast Schizosaccharomyces pombe is a unique biological process in that the plasma membrane of daughter cells is assembled de novo within the mother cell cytoplasm. A double unit membrane called the forespore membrane (FSM) is constructed dynamically during meiosis. To obtain a dynamic view of FSM formation, we visualized FSM in living cells by using green fluorescent protein fused with Psy1, an FSM-resident protein, together with the nucleus or microtubules. The assembly of FSM initiates in prophase II, and four FSMs in a cell expand in a synchronous manner at the same rate throughout meiosis II. After the meiosis II completes, FSMs continue to expand until closure to form the prespore, a spore precursor. Prespores are initially ellipsoidal, and eventually become spheres. FSM formation was also observed in the sporulation-deficient mutants spo3, spo14, and spo15. In the spo15 mutant, the initiation of FSM formation was completely blocked. In the spo3 mutant, the FSM expanded normally during early meiosis II, but it was severely inhibited during late and postmeiosis, whereas in the spo14 mutant, membrane expansion was more severely inhibited throughout meiosis II. These observations suggest that FSM expansion is composed of two steps, early meiotic FSM expansion and late and post meiotic FSM expansion. Possible regulatory mechanisms of FSM formation in fission yeast are discussed.

Present address: Radiation Biology Center, Kyoto University, Yoshida-Konoe-cho, Sakyo-ku, Kyoto 606-8501, Japan.

Address correspondence to: Taro Nakamura (taronaka{at}sci.osaka-cu.ac.jp)

Abbreviations used: CFP, cyan fluorescent protein; ER, endoplasmic reticulum; FSM, forespore membrane; GFP, green fluorescent protein; SPB, spindle pole body; YFP, yellow fluorescent protein.