Baatout Sarah, Müller Wolfgang, Michaux Arlette, Buset Jasmine, Schoonjans Werner, Jacquet Paul
Laboratory of Molecular and Cellular Biology, Institute for Health, Environment and Safety, Belgian Nuclear Research Center, SCK-CEN, Mol, Belgium.
In Vivo. 2007 Jul-Aug;21(4):571-82.
The cdk1/cyclin B1 complex is a universal regulator known to be responsible for driving the cell-cycle from the G2- to the M-phase. To investigate the effects of irradiation on the activity of this complex in preimplantation embryos, we irradiated one- and two-cell mouse embryos with X-rays, and measured the fluctuations of histone H1 and cdk1 kinase activity. Four mouse strains with different radiation sensitivities were chosen: the BALB/c and the Heiligenberger (radiation-sensitive) and the C57BL and the CF1 (radiation-resistant) strains. Embryos irradiated in the first cell-cycle arrested in the G2-phase. However, the dynamics of this radiation-induced G2-block were different between the mouse strains tested. Indeed, in the C57BL and the CF1 strains, X-irradiation with 2.5 Gy induced a very short G2 block before the one-cell embryos could then proceed to mitosis. On the contrary, X-irradiation in BALB/c induced a G2-arrest that lasted about 20 h, with the percentage of embryos blocked in G2 depending on the dose, whilst in the Heiligenberger strain, all irradiated embryos developed a G2-block, which was dependent in duration on the radiation dose. In all mouse strains, the histone H1 kinase activity remained low during the G2 arrest, while it showed values comparable to that of control embryos during mitosis. X-irradiation is known to induce a change in the phosphorylation state of the cdk1 protein kinase in adult somatic cells. In embryos from the BALB/c and C57BL strains, the histone H1 kinase activities were confirmed by the cdk1 phosphorylation pattern: the inactive and phosphorylated form of cdk1 was observed in G2 arrested 1-cell embryos, while the active and dephosphorylated form of cdk1 was present in dividing control and irradiated 1-cell embryos. X-irradiation at the 2-cell stage only induced a short G2-arrest in all tested mouse strains. In conclusion, cell-cycle effects in early embryos under normal conditions and after irradiation are strictly paralleled by changes in the activity of the central cell-cycle driving enzyme complex.
细胞周期蛋白依赖性激酶1/细胞周期蛋白B1复合物（cdk1/cyclin B1复合物）是一种普遍的调节因子，已知其负责驱动细胞周期从G2期进入M期。为了研究辐射对植入前胚胎中该复合物活性的影响，我们用X射线照射单细胞和双细胞小鼠胚胎，并测量组蛋白H1和cdk1激酶活性的波动。选择了四种具有不同辐射敏感性的小鼠品系：BALB/c和海利根贝格（辐射敏感）品系以及C57BL和CF1（辐射抗性）品系。在第一个细胞周期接受照射的胚胎停滞在G2期。然而，在所测试的小鼠品系中，这种辐射诱导的G2期阻滞的动态变化有所不同。确实，在C57BL和CF1品系中，2.5 Gy的X射线照射在单细胞胚胎进入有丝分裂之前诱导了非常短暂的G2期阻滞。相反，BALB/c品系中的X射线照射诱导了持续约20小时的G2期停滞，G2期阻滞的胚胎百分比取决于剂量，而在海利根贝格品系中，所有受照射的胚胎都出现了G2期阻滞，其持续时间取决于辐射剂量。在所有小鼠品系中，组蛋白H1激酶活性在G2期停滞期间保持较低水平，而在有丝分裂期间其活性与对照胚胎相当。已知X射线照射会诱导成年体细胞中cdk1蛋白激酶的磷酸化状态发生变化。在BALB/c和C57BL品系的胚胎中，组蛋白H1激酶活性通过cdk1磷酸化模式得到证实：在G2期停滞的单细胞胚胎中观察到cdk1的无活性和磷酸化形式，而在分裂的对照和受照射的单细胞胚胎中存在cdk1的活性和去磷酸化形式。在双细胞阶段进行X射线照射仅在所有测试的小鼠品系中诱导了短暂的G2期阻滞。总之，正常条件下和照射后早期胚胎中的细胞周期效应与核心细胞周期驱动酶复合物活性的变化严格平行。
