Cell polarity
In biology, cell polarity is a polar morphology of a cell , i.e. a specific alignment of cell structures. Cell polarity plays a fundamental role in various cellular processes, such as cell migration, asymmetric cell division and tissue homeostasis . Accordingly, many different cell types can have polarity, e.g. B. epithelial cells, neurons and egg cells.
Polarity in epithelia
Epithelial cells can be divided into an apical and a basal pole and thus define a longitudinal axis through the cell. Since the polarity of cells not only influences the structural difference but also the functional differences between the apical and basal membrane of a cell, one speaks in this context of an apical and basolateral domain.
In the case of an epithelium , the apical pole of a cell is defined based on its orientation towards the external environment. The external environment can be the outside world (e.g. skin) or the lumen (e.g. intestines ). The basal pole, on the other hand, points to the inner milieu or the basal lamina . The lateral surfaces form those that border the neighboring cells. A good example of this is the intestinal lining . The apical side of the epithelial cells in the intestine faces the intestinal contents. To increase the surface area, these cells have a so-called brush border, so-called microvilli, on their apical side . The basal side, on the other hand, faces a delicate layer of connective tissue (Lamina propria mucosae) and a fine muscle layer ( Lamina muscularis mucosae ).
In other cells without a “milieu”, the cell polarity is determined on the basis of characteristic subcellular structures. Like the already mentioned microvilli, stereocilia or cinema cilia , for example, are always at the apical pole. An example of this are sensory cells such as photoreceptors in the eye . The cuticula or crusta on the apical side are also excreted (e.g. adamantoblasts ). The side surfaces, however, often have tight junctions or adherent junctions .
literature
- M. Simons, M. Mlodzik: Planar Cell Polarity Signaling: From Fly Development to Human Disease. In: Annu Rev Genet. 2008 Aug 18. PMID 18710302
- E. Assémat et al: Polarity complex proteins. In: Biochim Biophys Acta . 2008 Mar; 1778 (3), pp. 614-630. PMID 18005931
Individual evidence
- ^ Enrique Rodriguez-Boulan, Ian G. Macara: Organization and execution of the epithelial polarity program . In: Nature Reviews Molecular Cell Biology . tape 15 , no. 4 , April 2014, ISSN 1471-0072 , p. 225–242 , doi : 10.1038 / nrm3775 ( nature.com [accessed May 27, 2018]).