The cadherin superfamily: diversity in form and function.

Over recent years cadherins have emerged as a growing superfamily of molecules, and a complex picture of their structure and their biological functions is becoming apparent. Variation in their extracellular region leads to the large potential for recognition properties of this superfamily. This is demonstrated strikingly by the recently discovered FYN-binding CNR-protocadherins; these exhibit alternative expression of the extracellular portion, which could lead to distinct cell recognition in different neuronal populations, whereas their cytoplasmic part, and therefore intracellular interactions, is constant. Diversity in the cytoplasmic moiety of the cadherins imparts specificity to their interactions with cytoplasmic components; for example, classical cadherins interact with catenins and the actin filament network, desmosomal cadherins interact with catenins and the intermediate filament system and CNR-cadherins interact with the SRC-family kinase FYN. Recent evidence suggests that CNR-cadherins, 7TM-cadherins and T-cadherin, which is tethered to the membrane by a GPI anchor, all localise to lipid rafts, specialised cell membrane domains rich in signalling molecules. Originally thought of as cell adhesion molecules, cadherin superfamily molecules are now known to be involved in many biological processes, such as cell recognition, cell signalling, cell communication, morphogenesis, angiogenesis and possibly even neurotransmission.