Department of Biology, Stanford University, Stanford, CA 94305, USA.
Department of Biology, Stanford University, Stanford, CA 94305, USA; Howard Hughes Medical Institute, Stanford University, Stanford, CA 94305, USA.
Curr Biol. 2017 Mar 20;27(6):877-883. doi: 10.1016/j.cub.2017.01.059. Epub 2017 Mar 9.
Mechanical information is an important contributor to cell polarity in uni- and multicellular systems [1-3]. In planar tissues like the Drosophila wing, cell polarity reorients during growth as cells divide and reorganize [4]. In another planar tissue, the Arabidopsis leaf epidermis [5], polarized, asymmetric divisions of stomatal stem cells (meristemoid mother cells [MMCs]) are fundamental for the generation and patterning of multiple cell types, including stomata. The activity of key transcription factors, polarizing factors [6], and peptide signals [7] explains some local stomatal patterns emerging from the behavior of a few lineally related cells [6, 8-11]. Here we demonstrate that, in addition to locally acting signals, tissue-wide mechanical forces can act as organizing cues, and that they do so by influencing the polarity of individual MMCs. If the mechanical stress environment in the tissue is altered through stretching or cell ablations, cellular polarity changes in response. In turn, polarity predicts the orientation of cellular and tissue outgrowth, leading to increased mechanical conflicts between neighboring cells. This interplay among growth, oriented divisions, and cell specification could contribute to the characteristic patterning of stomatal guard cells in the context of a growing leaf.
机械信息是单细胞和多细胞系统中细胞极性的重要贡献者[1-3]。在像果蝇翅膀这样的平面组织中，随着细胞分裂和重组，细胞极性在生长过程中重新定向[4]。在另一个平面组织，拟南芥叶表皮[5]中，气孔干细胞（分生母细胞[MMC]）的极化、不对称分裂对于多种细胞类型的产生和模式形成是基础，包括气孔。关键转录因子、极化因子[6]和肽信号[7]的活性解释了一些局部气孔模式的出现，这些模式是由少数线性相关细胞的行为产生的[6,8-11]。在这里，我们证明，除了局部作用的信号外，组织范围的机械力也可以作为组织线索，它们通过影响单个 MMC 的极性来发挥作用。如果组织中的机械应力环境通过拉伸或细胞消融而改变，细胞极性会相应改变。反过来，极性预测了细胞和组织生长的方向，导致相邻细胞之间的机械冲突增加。这种生长、定向分裂和细胞特化之间的相互作用可能有助于在不断生长的叶片中气孔保卫细胞的特征模式形成。
