All animal work was done in accordance to the ARVO statement for the Use of Animals in Ophthalmic and Vision Research, and with approval from the Institutional Animal Care and Use Committee at the University of Colorado. Animals of both genders were used for all studies. The following Cre-driver lines were used: Tg(Cdh5-cre/ERT2)1Rha 50 (link), Pdgfrb(BAC)−CreERT2 51 (link), and Rx-Cre 52 (link), the latter kindly provided by Drs. Eric Swindell and Milan Jamrich. mT/mG reporter mice were obtained from Jackson Laboratories. Conditional knock out mice were generated by first breeding Tspan12+/− mice with each Cre driver line (heterozygous for the transgene), then breeding Tspan12+/−; Cre+ mice with Tspan12flox/flox mice. The alleles Tspan12flox (Tspan12tm1.1Hjug) and Tspan12- (Tspan12tm1.2Hjug) were generated by gene targeting as described below.