Elucidation of regulatory mechanisms coordinating forespore membrane assembly with meiotic nuclear divisions

前孢子膜是在裂殖酵母第二次减数分裂过程中形成的。前孢子膜组装与减数分裂进程的协调对于将整个基因组准确传递到孢子至关重要。为了阐明这一偶联机制，对粟酒裂殖酵母减数分裂Ⅰ前孢子膜组装阻遏缺陷突变体进行了研究。我们分离并分析了gis突变体，这些突变体优先形成两点子囊。这些gis突变体在减数分裂L时启动前孢子膜。gis基因已被鉴定为β-微管蛋白、Alp 7和Alp 14，它们都参与纺锤体形成或纺锤体/动粒附着。用微管解聚药物TBZ处理野生型细胞，在gis突变体中诱导了双孢子样腹水。为了检查纺锤体检查点在gis突变体中是否被激活，将mad 2突变引入到相应的gis突变体中。大多数双重突变体都是致命的。gis 1 mad 2双突变体由于纺锤体组装检查点缺陷，部分抑制gist单突变体的表型，从而形成正常的四孢子囊。在gis 1 mad 2双突变体中，中期I的持续时间显著延长，这表明在mad 2突变体中几乎没有观察到TBZ诱导的纺锤体组装检查点的激活.这些结果支持了第一次减数分裂的延迟是导致减数分裂Ⅰ前孢子膜早熟形成的原因。

The forespore membrane is formed during second meiotic division in fission yeast. The coordination of the forespore membrane assembly with the progression of meiotic divisions is crucial for accurate transmission of the whole genome to spores.1. In order to elucidate this coupling mechanism, the mutants of S pombe that are defective in repression of the forespore membrane assembly in meiosis I. We isolated and analyzed gis mutants that forms preferentially two-spoted asci. These gis mutants initiate the forespore membrane at meiosis L The gis genes have been identified as β-tubulin, Alp7 and Alp14, all of which are involved in spindle formation or spindle/kinetochore attachment. Treatment of wild-type cells with the microtubule-depolymerizing drug, TBZ, induced two-spored asci like in gis mutants.2. To examine whether spindle checkpoint is activated in the gis mutants, the mad2 mutation was introduced into the respective gis mutants. Most of these double mutants are lethal. The gis1 mad2 double mutants, which are defective in spindle assembly checkpoint, partially suppressed the phenotypes of the gist single mutants, thus form normal four-spored ascus. In the gis1 mad2 double mutants, the duration of the metaphase I is considerably extended, suggesting activation of the spindle assembly checkpoint TBZ-induced formation of two-spored asci is scarcely observed in mad2 mutants.3. These results support the idea that the delay of the first meiotic division is responsible for the precocious formation of the forespore membrane at meiosis I.