What is Apico basal polarity?

Definition. Apicobasal polarity is a type of cell polarity specific to epithelial cells, referring to a specialised apical membrane facing the outside of the body or lumen of internal cavities, and a specialised basolateral membrane localised at the opposite side, away from the lumen.

What maintains cell polarity?

Once established, cell polarity is maintained by transcytosis, in which vesicles carry incorrectly-localized membrane proteins to the correct regions in the plasma membrane. In addition, tight junctions, which act as ‘fences’ against transmembrane diffusion, lock the asymmetry in place.

What does polarity in epithelial cells mean?

Cell polarity is characterised by differences in structure, composition and function between at least two poles of a cell. In epithelial cells, these spatial differences allow for the formation of defined apical and basal membranes.

Do epithelial cells exhibit polarity?

The epithelial cells exhibit polarity with differences in structure and function between the exposed or apical facing surface of the cell and the basal surface close to the underlying body structures.

How is the apical and baso-lateral polarity maintained?

The sharp distinction between apical and baso-lateral domains is maintained by an active mechanism that prevents mixing. The nature of this mechanism is not known, but it clearly depends on the polarity determinants. In the absence of the aPKC complex, the baso-lateral determinants spread into the former apical domain.

How are basal and lateral membranes related to polarity?

Basal and lateral membranes share common determinants, the proteins LLGL1, DLG1, and SCRIB. These three proteins all localize to the basolateral domain and are essential for basolateral identity and for epithelial polarity. How epithelial cells polarize is still not fully understood.

Where are the molecules located in the apical membrane?

A variety of molecules are located at the apical membrane, but only a few key molecules act as determinants that are required to maintain the identity of the apical membrane and, thus, epithelial polarity. These molecules are the proteins Cdc42, atypical protein kinase C (aPKC), Par6, Par3 /Bazooka/ASIP.

Why are apical proteins trafficked from the Golgi to the apical membrane?

Apical membrane proteins are trafficked from the Golgi to the apical, rather than baso-lateral, membrane because apical determinants serve to identify the correct destination for vesicle delivery. A related mechanism is likely to operate for the baso-lateral membranes. The fourth principle is lipid modification.