Epithelial polarity

How epithelial cells generate and maintain polarity remains unclear, but certain molecules have been found to play a key role.

The principal function of this basolateral membrane is to take up metabolic waste products into the epithelial cell for disposal into the lumen where it is transported out of the body as urine.

A secondary role of the basolateral membrane is to allow the recycling of desirable substrates, such as glucose, that have been rescued from the lumen of the tubule to be secreted into the interstitial fluids.

In similar models, researchers have shown that epithelial cells can self-assemble into a rich set of robust biological shapes.

[3] In the yeast saccharomyces cerevisiae, there is genetic evidence that Cdc42 is subject to positive feedback of this kind and can spontaneously polarize, even in the absence of an external cue.

The sharp distinction between apical and baso-lateral domains is maintained by an active mechanism that prevents mixing.

Conversely, in the absence of any of Lgl, Dlg or Scrib, the apical determinants spread into the former baso-lateral domain.

Certain molecules, such as Integrins, localise specifically to the basal membrane and form connections with the extracellular matrix.

[4] All epithelial cells express the transmembrane adhesion molecule E-cadherin, a cadherin which localises most prominently to the junction between the apical and lateral membranes.

The intra-cellular domains of E-cadherin molecules bind to the actin cytoskeleton via the adaptor proteins alpha-catenin and beta-catenin.

Bruce Alberts; Alexander Johnson; Julian Lewis; Martin Raff; Keith Roberts; Peter Walter, eds.