Functional analysis of Cyclin A/Cdk2 for chromosome condensation

我们已经表明，非洲爪蟾细胞周期蛋白B2是通过其胞质滞留信号（CRS）区域参与双极纺锤体的形成。然而，在细胞周期蛋白B2的CRS区域中存在的NES样序列（NELS）可能参与双极纺锤体的形成。我们在这里表明，细胞周期蛋白B2实际上是出口从细胞核通过其NELS，但细胞周期蛋白B2 CRS区的过度表达，具有突变的NELS，仍然抑制双极纺锤体形成卵母细胞。相比之下，过表达缺少C-末端7个氨基酸的细胞周期蛋白B2 CRS区域不再抑制卵母细胞或胚胎中双极纺锤体的形成。这些结果表明，CRS区域，特别是其C-末端的7个酸性残基，细胞周期蛋白B2是必需的双极纺锤体的形成在减数分裂和有丝分裂的细胞divisions.In成熟非洲爪蟾卵母细胞，细胞周期调节剂和pre-MPF存储准备带来一个特定的细胞周期卵母细胞的成熟。我们研究了这些细胞周期调节因子的表达模式以及卵子发生过程中前MPF的形成。Cdc 2和Cyclin B2已经存在于I期卵母细胞中，并且在I期卵母细胞中也检测到前MPF形成。MPF的负调控因子Myt 1和Chk 1在卵子发生早期即已合成。而MPF的正调控因子MEK、MAPK和Cdc 25 C则主要在卵子发生后期合成。北方印迹分析表明，这些细胞周期调节因子的合成是由翻译控制的。

We have shown that Xenopus cyclin B2 is involved in bipolar spindle formation through its cytoplasmic retention signal (CRS) region. However, an NES-like sequence (NELS) present in the CRS region of cyclin B2 might be involved in bipolar spindle formation. We show here that cyclin B2 is actually exported from the nucleus via its NELS, but that overexpression of the cyclin B2 CRS region, having a mutated NELS, still inhibits bipolar spindle formation in oocytes. In contrast, overexpression of the cyclin B2 CRS region lacking its C-terminal seven amino acids no longer inhibits bipolar spindle formation in oocytes or embryos. These results suggest strongly that the CRS region, especially its C-terminal seven acidic residues, of cyclin B2 is required for bipolar spindle formation in both the meiotic and mitotic cell divisions.In full-grown Xenopus oocytes, cell-cycle regulators and pre-MPF are stored ready to bring about a specific cell cycle for oocyte maturation. We examined the expression pattern of these cell-cycle regulators as well as pre-MPF formation during oogenesis. Cdc2 and Cyclin B2 were already present in stage I oocytes and pre-MPF formation was also detected in stage I oocytes. Some negative regulators of MPF, Myt1 and Chk1, were synthesized early in oogenesis. In contrast, positive regulators of MPF, MEK, MAPK and Cdc25C, were mainly synthesized late in oogenesis. Northern blotting analysis suggested that the synthesis of these cell-cycle regulators was controlled by translation.