(Figures 3D–F). Like the 3 C-type genes, the 3 A-type genes are also expressed in these cell types in the developing retina (Figures S3A-B), indicating that the full spectrum of Pcdhg isoforms are not required for neuronal survival. Increased levels of apoptosis observed in Pcdhgfcon3/tcko trans-heterozygous retinas (Figures 3G-G’) are consistent with the previous finding in Pcdhgfcon3/fcon3 mutants that cell loss and the consequent thinning of IPL is due to elevated programmed cell death (Lefebvre et al., 2008). As with Pcdhgfcon3/fcon3 mutants, targeting of interneurons and RGC dendrites to appropriate IPL laminae was intact in Pcdhgfcon3/tcko trans-heterozygous mutants (Figures 3H-H’). Therefore, in the retina as in the spinal cord, removal of the 3 C-type isoforms results in elevated neuronal apoptosis and loss of specific neuronal subtypes at similar levels and patterns as deletion of all 22 Pcdhg isoforms.
