Fig. 1. ptf1a regulatory elements drive expression of GFP in amacrine cells in transgenic zebrafish. (A) Confocal images of a cryosectioned retina from a ptf1a::GFP fish at 76 hpf reveal a population of GFP⁺ cells in the inner portion of the INL and a population of cells in the GCL that are immunoreactive for the 5E11 antigen, suggesting they are amacrine cells (arrows in the GCL indicate displaced amacrine cells). The arbors of both amacrine cell populations ramify in the IPL, forming a laminated plexus. Horizontal cells (H) located in the outer part of the INL also express GFP. (B) In vivo confocal time-lapse images of a vitreally located GFP⁺ amacrine cell co-labeled with membrane-targeted mCherry (red) driven by an -tubulin promoter reveal that its neurites are oriented towards the INL. (C) In vivo confocal time-lapse images reveal that both populations of GFP⁺ amacrine cells (green) can be identified as early as 39 hpf. The vitreally located GFP⁺ cells with rounded or flattened somata (arrows) become displaced to the GCL as a plexus forms (black arrowheads, 51 hpf) between them and the INL population of GFP⁺ amacrine cells (46 and 51 hpf). Counterstaining with BODIPY Texas Red demonstrates that the GFP⁺ plexus lies within the forming IPL. Gray-scale images of GFP⁺ amacrine cells are shown to permit better visualization of GFP⁺ processes.