The Pcdhg fcon3 conditional mutant allele, in which the third constant exon is flanked by loxP sequences and which generates a functionally null allele following Cre recombination, was described previously21,22. Retina-specific Chx10-cre31 and Six3-cre transgenic mice32 were provided by Constance Cepko (Harvard) and William Klein (M.D. Anderson Cancer Center) respectively. Bax−/− mutants33, Purkinje-specific L7Bac-cre transgenic mice34, Chat-cre, in which the Cre recombinase gene was targeted to the endogenous ChAT gene35, and Rosa-CAG-LoxP-STOP-LoxP-tdTomato-WPRE reporter mice36 were obtained from Jackson Laboratories. A line of BAC transgenic mice in which regulatory elements from the fstl4 gene drive expression of CreER was generated as described in ref. 37. In this line, called line 1 to distinguish it from the line called “BD” in ref. 37, CreER was expressed in SACs, as well as sparse other amacrine cells. We believe that expression reflects influences at the site of transgene integration rather than expression of fstl4. Thy1-OFP3 transgenic mice, in which Thy1 promoter and regulatory elements direct expression of Kusabira Orange (OFP) in SACs and subset of RGCs, were described previously37. Pcdhgtcko and Pcdhgtako mice were
