Fig. 2. Development of the zebrafish retinotectal projection in vivo. EGFP expression signals in RGCs of transgenic zebrafish embryos were followed at various developmental stages by confocal laser scanning microscopy.e, Eye; h, hypophysis; tg, trigeminal ganglion cells; y, yolk; t, tectum. Scale bars: A–F, 100 μm; D,inset, 30 μm; G–J, 50 μm. A, B, Lateral (A) and frontal (B) views of the head of an embryo at 30 hpf. EGFP signals were detected at the ventral retina (arrowheads). C, D, Lateral (C) and frontal (D) views of the head of an embryo at 36 hpf. D,Inset, RGC axons crossing optic chiasm. E, F, Lateral (E) and frontal (F) views of the head of an embryo at 48 hpf.G–L, Lateral views of the tectum of an embryo at 54 (G), 60 (H), 76 (I), 84 (J), 100 (K), and 124 (L) hpf.Dashed lines indicate the area of the tectal neuropil, and asterisks indicate the pretectal arborization field of RGC axons. Arrows point to the rostrolateral margin in which RGC axons entered the tectum. G,Inset, Lateral view of the head of the embryo at 54 hpf.r, Rostral; l, lateral; c, caudal; m, medial. Arrowhead inL indicates the axonal bundle in the tectum.