Pérez-Mongiovi D, Chang P, Houliston E
Unité de Biologie Cellulaire Marine, ERS 643 CNRS-Université Paris VI, Station Zoologique, 06230 Villefranche-sur-mer, France.
J Cell Sci. 1998 Feb;111 ( Pt 3):385-93. doi: 10.1242/jcs.111.3.385.
During the period of mitosis, two surface contraction waves (SCWs) progress from the animal to vegetal poles of the Xenopus egg. It has been shown that these SCWs occur in parallel with the activation of MPF and with its subsequent inactivation in the animal and vegetal hemispheres, suggesting that they are responses to propagated waves of MPF activity across the egg. We have analysed the mechanism of MPF regulation in different regions of the egg in detail in relation to SCW progression. The distributions of histone HI kinase activity and of Cdc2 and cyclin B (the catalytic and regulatory subunits of MPF) were followed by dissection of intact eggs following freezing and in cultured fragments separated by ligation. Cdc2 was found to be distributed evenly throughout the egg cytoplasm. Loss of phosphorylated (inactive) forms of Cdc2 coincided spatially with the wave of MPF activation, while cyclin B2 accumulation occurred in parallel in animal and vegetal regions. In ligated vegetal pole fragments no MPF activation or Cdc2 dephosphorylation were detectable. A wave of cyclin B destruction that occurred in concert with the second SCW was also blocked. Taken together these results indicate that the triggering mechanism for MPF activation requires components specific to the animal cytoplasm, acting via Cdc2 dephosphorylation, and that MPF activation subsequently propagates autocatalytically across the egg. SCW progression in the vegetal hemisphere was followed directly by time-lapse videomicroscopy of subcortical mitochondrial islands. The first SCW traversed the vegetal pole at the time of MPF activation in this region. Like MPF activation and inactivation, SCWs were blocked in the vegetal region by ligation. These observations reinforce the hypothesis that the first SCW is a direct consequence of the MPF activation wave. It may reflect depolymerisation of the subcortical microtubule network since it coincided exactly with the arrest of the microtubule-dependent movement of 'cortical rotation' and was related in direction in most eggs. The cyclin B destruction wave and associated cortical contraction of the second SCW may be localised downstream consequences of the MPF activation wave, or they may propagate independently from the animal cytoplasm.
在有丝分裂期间，爪蟾卵上会出现两道表面收缩波（SCW），从动物极向植物极推进。研究表明，这些表面收缩波与MPF的激活以及随后在动物半球和植物半球的失活同时发生，这表明它们是对MPF活性在卵内传播波的反应。我们详细分析了卵不同区域中MPF调节机制与表面收缩波推进的关系。通过冷冻后解剖完整的卵以及对结扎分离的培养片段进行分析，追踪组蛋白H1激酶活性以及Cdc2和周期蛋白B（MPF的催化亚基和调节亚基）的分布情况。发现Cdc2均匀分布于整个卵细胞质中。Cdc2磷酸化（无活性）形式的消失在空间上与MPF激活波一致，而周期蛋白B2在动物区和植物区同时积累。在结扎的植物极片段中，未检测到MPF激活或Cdc2去磷酸化。与第二道表面收缩波同时发生的周期蛋白B降解波也被阻断。综合这些结果表明，MPF激活的触发机制需要动物细胞质特有的成分，通过Cdc2去磷酸化起作用，并且MPF激活随后在整个卵内自动催化传播。通过对皮层下线粒体岛的延时视频显微镜观察直接追踪了植物半球表面收缩波的推进情况。第一道表面收缩波在该区域MPF激活时穿过植物极。与MPF激活和失活一样，表面收缩波在植物区被结扎阻断。这些观察结果强化了第一道表面收缩波是MPF激活波直接结果的假说。它可能反映了皮层下微管网络的解聚，因为它恰好与微管依赖的“皮层旋转”运动的停止同时发生，并且在大多数卵中方向相关。第二道表面收缩波的周期蛋白B降解波和相关的皮层收缩可能是MPF激活波的局部下游结果，或者它们可能从动物细胞质独立传播。
