Figure 1. Evaluation of enhancer trap vectors. To test background expression from the enhancer trap vectors Hsp68-LacZ, ptkEGFP, or Stagia3, embryonic chicken retinas were electroporated, and reporter gene expression analyzed. A: Chicken embryonic development indicated by days and stages, according to Hamburger and Hamilton [38]. Important time points in neurogenesis [28] are indicated by arrows. B–E: Diagrams of the trap vectors and fluorescence micrographs of the retinal explants electroporated at stages 22–25 and analyzed after 24 h.