Polarization along an apico-basolateral axis is a hallmark of epithelial cells and is essential for their selective barrier and transporter functions, as well as for their ability to provide mechanical resiliency to organs. Loss of polarity along this axis perturbs development and is associated with a wide number of diseases. We describe three steps involved in polarization: symmetry breaking, polarity establishment, and polarity maintenance. While the proteins involved in these processes are highly conserved among epithelial tissues and species, the execution of these steps varies widely and is context dependent. We review both theoretical principles underlying these steps and recent work demonstrating how apico-basolateral polarity is established in vivo in different tissues, highlighting how developmental and physiological contexts play major roles in the execution of the epithelial polarity program.

中文翻译：

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一个极化问题：体内顶端基底外侧极化机制的多样性。

沿顶端-基底外侧轴的极化是上皮细胞的标志，对于它们的选择性屏障和转运蛋白功能以及它们为器官提供机械弹性的能力至关重要。沿该轴失去极性会扰乱发育并与多种疾病有关。我们描述了极化涉及的三个步骤：对称破坏、极性建立和极性维持。虽然参与这些过程的蛋白质在上皮组织和物种中高度保守，但这些步骤的执行差异很大并且取决于上下文。我们回顾了这些步骤背后的理论原理和最近的工作，展示了如何在体内不同组织中建立顶基-基底外侧极性，