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 generated using standard gene targeting techniques28. Mice were maintained on a C57/B6J background. All experiments were carried out in accordance with protocols approved by the Harvard University Standing Committee on the Use of Animals in Research and Teaching.
