Itadani Akiko, Nakamura Taro, Hirata Aiko, Shimoda Chikashi
Department of Biology, Graduate School of Science, Osaka City University, Sugimoto, Sumiyoshi-ku, Osaka 558-8585, Japan.
Eukaryot Cell. 2010 Dec;9(12):1925-35. doi: 10.1128/EC.00022-10. Epub 2010 Sep 10.
Calmodulin in Schizosaccharomyces pombe is encoded by the cam1(+) gene, which is indispensable for both vegetative growth and sporulation. Here, we report how Cam1 functions in spore formation. We found that Cam1 preferentially localized to the spindle pole body (SPB) during meiosis and sporulation. Formation of the forespore membrane, a precursor of the plasma membrane in spores, was blocked in a missense cam1 mutant, which was viable but unable to sporulate. Three SPB proteins necessary for the onset of forespore membrane formation, Spo2, Spo13, and Spo15, were unable to localize to the SPB in the cam1 mutant although five core SPB components that were tested were present. Recruitment of Spo2 and Spo13 is known to require the presence of Spo15 in the SPB. Notably, Spo15 was unstable in the cam1 mutant, and as a result, SPB localization of Spo2 and Spo13 was lost. Overexpression of Spo15 partially alleviated the sporulation defect in the cam1 mutant. These results indicate that calmodulin plays an essential role in forespore membrane formation by stably maintaining Spo15, and thus Spo2 and Spo13, at the SPB in meiotic cells.
粟酒裂殖酵母中的钙调蛋白由cam1(+)基因编码，该基因对于营养生长和孢子形成均不可或缺。在此，我们报告了Cam1在孢子形成中的作用方式。我们发现，在减数分裂和孢子形成过程中，Cam1优先定位于纺锤体极体（SPB）。前孢子膜是孢子中质膜的前体，在一个错义cam1突变体中其形成受阻，该突变体能够存活但无法形成孢子。尽管所检测的五个核心SPB成分都存在，但前孢子膜形成起始所必需的三种SPB蛋白Spo2、Spo13和Spo15在cam1突变体中无法定位于SPB。已知Spo2和Spo13的募集需要SPB中存在Spo15。值得注意的是，Spo15在cam1突变体中不稳定，结果导致Spo2和Spo13失去SPB定位。Spo15的过表达部分缓解了cam1突变体中的孢子形成缺陷。这些结果表明，钙调蛋白通过在减数分裂细胞的SPB处稳定维持Spo15，进而稳定维持Spo2和Spo13，在孢子膜形成中发挥重要作用。
