Protocadherin-17 (Pcdh17) belongs to the delta-2 subfamily of nonclustered protocadherins. The non-clustered PCDHs appear to have homophilic/heterophilc cell-cell adhesion properties [], and the delta-2 subfamily (comprising protocadherin-8, -10, -17, -18, and -19) is widely expressed in the nervous system [, ]. Pcdh17 mediates collective axon extension in amygdala neurons [], regulates presynaptic assembly in corticobasal ganglia circuits [], and is involved in brain vascular development []. In addition, it has been shown to have a role in the formation of the zebrafish retina []and to act as a tumour suppressor [, ].The cadherin family consists of a large group of cell adhesion proteins. It can be classified into three subfamilies: classical cadherins, desmosomal cadherins and protocadherins (PCDHs). Based on the genomic structure, the PCDH family can be divided into two groups, clustered PCDHs and non-clustered PCDHs. Non-clustered PCDHs can be further classified into three subgroups: delta1 (PCDH1, PCDH7, PCDH9, PCDH11 and PCDH20), delta2 (PCDH8, PCDH10, PCDH12, PCDH17, PCDH18 and PCDH19) and epsilon (PCDH15, PCDH16, PCDH21 and MUCDHL). Non-clustered PCDHs are expressed predominantly in the nervous system and have spatiotemporally diverse expression patterns [].
