Molecular Genetics, Department of Biology, University of Utrecht, 3584 CH Utrecht, The Netherlands.
Cell. 2012 Aug 31;150(5):1002-15. doi: 10.1016/j.cell.2012.07.017. Epub 2012 Aug 23.
In plants, where cells cannot migrate, asymmetric cell divisions (ACDs) must be confined to the appropriate spatial context. We investigate tissue-generating asymmetric divisions in a stem cell daughter within the Arabidopsis root. Spatial restriction of these divisions requires physical binding of the stem cell regulator SCARECROW (SCR) by the RETINOBLASTOMA-RELATED (RBR) protein. In the stem cell niche, SCR activity is counteracted by phosphorylation of RBR through a cyclinD6;1-CDK complex. This cyclin is itself under transcriptional control of SCR and its partner SHORT ROOT (SHR), creating a robust bistable circuit with either high or low SHR-SCR complex activity. Auxin biases this circuit by promoting CYCD6;1 transcription. Mathematical modeling shows that ACDs are only switched on after integration of radial and longitudinal information, determined by SHR and auxin distribution, respectively. Coupling of cell-cycle progression to protein degradation resets the circuit, resulting in a "flip flop" that constrains asymmetric cell division to the stem cell region.
在植物中，由于细胞不能迁移，不对称细胞分裂（ACDs）必须局限在适当的空间背景中。我们研究了拟南芥根中干细胞女儿组织生成的不对称分裂。这些分裂的空间限制需要通过 RETINOBLASTOMA-RELATED（RBR）蛋白物理结合干细胞调节因子 SCARECROW（SCR）来实现。在干细胞龛中，通过 cyclinD6;1-CDK 复合物对 RBR 进行磷酸化，从而抵消 SCR 的活性。该 cyclin 本身受到 SCR 和其伴侣 SHORT ROOT（SHR）的转录控制，形成一个具有高或低 SHR-SCR 复合物活性的强大双稳态电路。生长素通过促进 CYCD6;1 转录来偏向这个电路。数学模型表明，只有在分别由 SHR 和生长素分布决定的径向和纵向信息整合后，ACD 才会被激活。细胞周期进程与蛋白质降解的耦合重置了电路，导致“翻转”，将不对称细胞分裂限制在干细胞区域。
