al., 2002; Wang et al., 2002a), which provides precise spatial and temporal controls over gene expression. As noted earlier, the C-type isoforms are phylogenetically unique among Pcdhs and exhibit distinct expression patterns. It remains to be seen whether just one of the three C-type genes is solely responsible for this function, or whether they work synergistically. We note that the two other C-type isoforms in the Pcdha cluster (Pcdhac1 and Pcdhac2) are dispensable for neuronal survival (Hasegawa et al., 2008; Katori et al., 2009), but they may play other specific roles yet to be identified. Further functional studies specifically targeting each of these C-type isoforms would be required to address these possibilities.
