 Moreover, these clustered Pcdh genes are predominantly expressed in the developing nervous system and since different subsets of Pcdhs genes are differentially expressed in individual neurons, a vast cell surface diversity may arise from this combinatorial expression.This has led to speculation and further to the proposal that Pcdhs may provide a synaptic-address code for neuronal connectivity or a single-cell barcode for self-recognition/self-avoidance similar to that ascribed to DSCAM proteins of invertebrates.Although vertebrate DSCAMs lack the diversity of their invertebrate counterparts, the selective transcription of individual Pcdh isoforms can be achieved by promoter choice followed by alternative pre-mRNA cis-splicing thus increasing the number of possible combinations.