Epithelial cells are the most common cell type in all animals, forming the sheets and tubes that compose most organs and tissues. Apical–basal polarity is essential for epithelial cell form and function, as it determines the localization of the adhesion molecules that hold the cells together laterally and the occluding junctions that act as barriers to paracellular diffusion. Polarity must also target the secretion of specific cargoes to the apical, lateral or basal membranes and organize the cytoskeleton and internal architecture of the cell. Apical–basal polarity in many cells is established by conserved polarity factors that define the apical (Crumbs, Stardust/PALS1, aPKC, PAR-6 and CDC42), junctional (PAR-3) and lateral (Scribble, DLG, LGL, Yurt and RhoGAP19D) domains, although recent evidence indicates that not all epithelia polarize by the same mechanism. Research has begun to reveal the dynamic interactions between polarity factors and how they contribute to polarity establishment and maintenance. Elucidating these mechanisms is essential to better understand the roles of apical–basal polarity in morphogenesis and how defects in polarity contribute to diseases such as cancer.

上皮细胞是所有动物中最常见的细胞类型，形成构成大多数器官和组织的片状和管状结构。顶端-基底极性对于上皮细胞的形成和功能至关重要，因为它决定了将细胞横向固定在一起的粘附分子的定位，以及作为细胞旁扩散障碍的封闭连接。极性还必须针对特定货物分泌到顶膜、侧膜或基底膜，并组织细胞的细胞骨架和内部结构。许多细胞的顶端-基底极性由定义顶端（Crumbs、Stardust/PALS1、aPKC、PAR-6 和 CDC42）、连接（PAR-3）和横向（Scribble、DLG、LGL、Yurt 和RhoGAP19D) 域，尽管最近的证据表明并非所有上皮细胞都通过相同的机制进行极化。研究已经开始揭示极性因素之间的动态相互作用以及它们如何促进极性的建立和维持。阐明这些机制对于更好地理解顶端-基底极性在形态发生中的作用以及极性缺陷如何导致癌症等疾病至关重要。