Hudson J W, Kozarova A, Cheung P, Macmillan J C, Swallow C J, Cross J C, Dennis J W
Samuel Lunenfeld Research Institute, Mount Sinai Hospital, Toronto, M5G 1X5, Ontario, Canada.
Curr Biol. 2001 Mar 20;11(6):441-6. doi: 10.1016/s0960-9822(01)00117-8.
Polo-like kinases in yeast, flies, and mammals regulate key events in mitosis. Such events include spindle formation at G2/M, the anaphase-promoting complex (APC) at the exit from mitosis, the cleavage structure at cytokinesis, and DNA damage checkpoints in G2/M. Polo-like kinases are distinguished by two C-terminal polo box (pb) motifs, which localize the enzymes to mitotic structures. We previously identified Sak, a novel polo-like kinase found in Drosophila and mammals. Here, we demonstrate that the Sak kinase has a functional pb domain that localizes the enzyme to the nucleolus during G2, to the centrosomes in G2/M, and to the cleavage furrow during cytokinesis. To study the role of Sak in embryo development, we generated a Sak null allele, the first polo-like kinase to be mutated in mice. Sak(-/-) embryos arrested after gastrulation at E7.5, with a marked increase in mitotic and apoptotic cells. Sak(-/-) embryos displayed cells in late anaphase or telophase that continued to express cyclin B1 and phosphorylated histone H3. Our results suggest that Sak is required for the APC-dependent destruction of cyclin B1 and for exit from mitosis in the postgastrulation embryo.
酵母、果蝇和哺乳动物中的Polo样激酶调节有丝分裂中的关键事件。这些事件包括G2/M期纺锤体的形成、有丝分裂末期促进复合物（APC）、胞质分裂时的分裂结构以及G2/M期的DNA损伤检查点。Polo样激酶的特征是具有两个C末端Polo框（pb）基序，这些基序将酶定位到有丝分裂结构上。我们之前鉴定出了Sak，一种在果蝇和哺乳动物中发现的新型Polo样激酶。在这里，我们证明Sak激酶具有功能性pb结构域，该结构域在G2期将酶定位到核仁，在G2/M期定位到中心体，在胞质分裂期间定位到分裂沟。为了研究Sak在胚胎发育中的作用，我们产生了一个Sak无效等位基因，这是第一个在小鼠中发生突变的Polo样激酶。Sak(-/-)胚胎在E7.5期原肠胚形成后停滞，有丝分裂和凋亡细胞显著增加。Sak(-/-)胚胎显示处于后期或末期的细胞继续表达细胞周期蛋白B1和磷酸化组蛋白H3。我们的结果表明，Sak是原肠胚形成后胚胎中依赖APC的细胞周期蛋白B1破坏和有丝分裂退出所必需的。
