PROTOCADHERINS - A LARGE FAMILY OF CADHERIN-RELATED MOLECULES IN CENTRAL-NERVOUS-SYSTEM

Using the polymerase chain reaction, we have isolated numerous rat and human cDNAs of which the deduced amino acid sequences are highly homo logous to the sequences of the extracellular domain of cadherins. The entire putative coding sequences for two human proteins defined by two of these cDNAs have been determined. The overall structure of these m olecules is very similar to that of classic cadherins, but they have s ome unique features. The extracellular domains are composed of six or seven subdomains that are very similar to those of cadherins, but have characteristic properties. The cytoplasmic domains, on the other hand , have no significant homology with those of classic cadherins. Since various cDNAs with almost identical features were obtained also from X enopus, Drosophila and Caenorhabditis elegans, it appears that similar molecules are expressed in a variety of organisms. We have tentativel y named these proteins protocadherins. They are highly expressed in br ain and their expression appears to be developmentally regulated. The proteins expressed from the two full-length cDNAs in L cells were appr oximately 170 or 150 kDa in size, and were localized mainly at cell-ce ll contact sites. Moreover, the transfectants showed cell adhesion act ivity.