apicalbasal

Apical-basal polarity refers to the organization of cells along an axis that extends from the apical surface, which faces the lumen or exterior, to the basal surface, which rests on the basement membrane. This arrangement creates distinct membrane domains with specialized proteins and functions, enabling directional transport, selective barriers, and organized tissue architecture. It is most extensively studied in epithelial tissues, where polarity underpins function and morphology.

Cell polarity is established and maintained by conserved protein complexes. The apical domain commonly contains the PAR complexes (PAR3, PAR6, and atypical PKC) together with the Crumbs complex, which promote apical identity and junction formation. The Scribble complex localizes to the basolateral surface and helps demarcate the boundary with the apical side. Tight and adherens junctions contribute to domain separation and tissue cohesion.

Polarity is reinforced by cytoskeletal organization and polarized vesicle trafficking. Microtubules and actin filaments orient with the apical and basolateral axes, guiding delivery of transporters, receptors, and enzymes to the correct membrane domain through Rab GTPases and SNAREs. Cell–cell adhesion at adherens junctions, mediated by E-cadherin, also helps maintain tissue-wide polarity.

During development, apical-basal polarity drives lumen formation, tissue morphogenesis, and barrier function. Loss or mislocalization of polarity components is associated with developmental defects and diseases, notably epithelial-to-mesenchymal transition in cancer, where cells lose apical-basal cues and gain migratory capacity.

Although the core concept is conserved in animals, other organisms and cell types display polarity with distinct molecular implementations. Neurons and plant cells exhibit apical-basal organization as well, though the specific polarity complexes and cues differ.