We considered the possibility that the indistinguishable phenotypes of Pcdhgtcko/tcko and Pcdhgdel/del mutants arise because the deletion of C-type exons, which are located immediately upstream of the constant exons, interferes with transcription and splicing of other Pcdhg genes, leading to a severely hypomorphic Pcdhg allele. To address this possibility, we first examined the expression of the remaining 19 A- and B-type Pcdhg genes in Pcdhgtcko/tcko brains. RT-PCR using exon-specific primers revealed that all 19 variable exons are expressed and correctly spliced to constant exons (Figures 4A-B). Western blotting indicated that Pcdhg total protein levels in Pcdhgtcko/tcko brains are similar to the wild type and even higher than those in Pcdhg full cluster deletion heterozygotes, which are phenotypically normal (Figure 4C). We next asked whether the remaining A- and B-type proteins in Pcdhgtcko/tcko mutants are functional. Several studies indicate that Pcdhg and Pcdha proteins interact, and may form multimeric complexes with Pcdhb proteins (Han et al., 2010; Murata et al., 2004; Schalm et al., 2010). Moreover, both Pcdha and Pcdhg proteins are tyrosine phosphorylated in mature neurons, suggesting that they mediate
