A novel zebrafish glra4a gene trap reveals expression in the zebrafish brain and spinal cord. (A) The zebrafish SAIGFF16B line contains the gene trap construct T2KSAGFF inserted between exons 1 and 2 of glra4a. This cassette contains a splice acceptor (SA), followed by an internal ribosome entry site (IRES), the coding region for the Gal4FF transcription activator and a polyadenylation site (pA). Gal4FF expression in SAIGFF16B was visualized by creating double transgenic fish carrying the Gal4FF transgene and a GFP reporter gene placed downstream of the Gal4-recognition sequence (UAS:GFP). (B,C) GFP expression in the glra4a gene-trap line at 48 hours post fertilization (hpf) reveals that glra4a is predominantly expressed four clusters of hindbrain commissural neurons and selected spinal commissural interneurons. (D) High magnification dorsal view of neurons indicated by arrows in (C). (E,F) Images show a portion of the zebrafish spinal cord at 48 hpf (E) and 72 hpf (F) showing glra4a expression in commissural primary (CoPA, white arrows) and secondary (CoSA, orange arrows). Scale bars: (B): 500 μm; (C); 250 μm; (D): 150 μm; (E,F): 50 μm.