Kwak Su-Hwan, Schiefelbein John
Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI 48109, USA.
Curr Biol. 2008 Dec 23;18(24):1949-54. doi: 10.1016/j.cub.2008.10.064.
Cellular pattern formation in the root epidermis of Arabidopsis occurs in a position-dependent manner, generating root-hair (H) cells contacting two underlying cortical cells and nonhair (N) cells contacting one cortical cell. SCRAMBLED (SCM), a leucine-rich repeat receptor-like kinase (LRR-RLK), mediates this process through its effect on a downstream transcription factor regulatory network. After perception of a positional cue, the SCM signaling pathway is proposed to preferentially repress WEREWOLF (WER) transcription factor expression in H cells and thereby bias the outcome of mutual lateral inhibition acting between H and N cells. However, the molecular mechanism responsible for this preferential SCM signaling is unknown. Here, we analyze the distribution of the SCM receptor and the biological effect of altering its accumulation pattern. We find that SCM expression and accumulation in the epidermal cell layer is necessary and sufficient to direct the cell-type pattern. Further, SCM preferentially accumulates in H cells, and this accumulation pattern is dependent on the downstream transcription factors. Thus, SCM participates in an autoregulatory feedback loop, enabling cells engaged in SCM signaling to maintain high levels of SCM receptor, which provides a simple mechanism for reinforcing a bias in receptor-mediated signaling to ensure robust pattern formation.
拟南芥根表皮中的细胞模式形成以位置依赖的方式发生，产生与两个下层皮层细胞接触的根毛（H）细胞和与一个皮层细胞接触的非根毛（N）细胞。富含亮氨酸重复序列的类受体激酶（LRR-RLK）SCRAMBLED（SCM）通过其对下游转录因子调控网络的作用介导这一过程。在感知到位置信号后，SCM信号通路被认为优先抑制H细胞中WEREWOLF（WER）转录因子的表达，从而使H细胞和N细胞之间相互侧向抑制的结果产生偏差。然而，负责这种优先SCM信号传导的分子机制尚不清楚。在这里，我们分析了SCM受体的分布以及改变其积累模式的生物学效应。我们发现SCM在表皮细胞层中的表达和积累对于指导细胞类型模式是必要且充分的。此外，SCM优先在H细胞中积累，并且这种积累模式依赖于下游转录因子。因此，SCM参与了一个自调节反馈回路，使参与SCM信号传导的细胞能够维持高水平的SCM受体，这为增强受体介导的信号偏差以确保稳健的模式形成提供了一种简单机制。
