Department of Biology, Graduate School of Science, Kobe University, Kobe 657-8501, Japan.
Protist. 2012 Mar;163(2):204-16. doi: 10.1016/j.protis.2011.07.007. Epub 2011 Aug 12.
In contrast to most ciliates, meiosis and successive nuclear changes during conjugation occur only in heterotypic pairs in Blepharisma. It has been suggested that homotypic pairs are ready for conjugation, but lack a trigger to initiate the nuclear changes, and the conjugation process is arrested before the onset of meiosis. To explore the possible nature of the trigger, we previously identified the genes BjCdk1 (homologous to cdk1/cdc2), Bj4HPPD (4-hydroxy-phenylpyruvate dioxygenase) and BjCks (cyclin dependent kinase regulatory subunit) whose expression is up-regulated in gamone1-treated type II cells. In this study, we investigated the molecular structures of these three genes, and compared their expression patterns in homotypic and heterotypic pairs, finding remarkable differences. BjCdk1, Bj4HPPD and BjCks were expressed specifically in gamone1-treated type II cells, but not in gamone2-treated type I cells. In heterotypic pairs, the expression of these genes stayed at the same level or gradually decreased throughout the entire process of conjugation, but it rapidly decreased and ceased after 10hours in homotypic pairs. These results indicate that some genes are expressed in a mating-type specific manner. Alternative gene expression in mating type I and type II cells and merging of individual factors in a heterotypic pair may induce nuclear changes including meiosis.
与大多数纤毛虫不同，在盘基网柄菌中，减数分裂和接合过程中的核变化仅发生在异型对中。有人认为同型对已经准备好进行接合，但缺乏启动核变化的触发因素，并且在减数分裂开始之前，接合过程被阻止。为了探索触发因素的可能性质，我们之前鉴定了 BjCdk1（与 cdk1/cdc2 同源）、Bj4HPPD（4-羟基苯丙酮酸双加氧酶）和 BjCks（细胞周期蛋白依赖性激酶调节亚基）的基因，它们在 gamone1 处理的 II 型细胞中的表达上调。在这项研究中，我们研究了这三个基因的分子结构，并比较了它们在同型和异型对中的表达模式，发现了显著的差异。BjCdk1、Bj4HPPD 和 BjCks 特异性表达在 gamone1 处理的 II 型细胞中，但不在 gamone2 处理的 I 型细胞中。在异型对中，这些基因的表达在整个接合过程中保持在同一水平或逐渐下降，但在同型对中，它们在 10 小时后迅速下降并停止。这些结果表明，某些基因以交配型特异性的方式表达。I 型和 II 型细胞中基因表达的替代以及异型对中个体因子的融合可能诱导包括减数分裂在内的核变化。
