To facilitate the identification and characterization of mutations
affecting the retina and photoreceptors in the zebrafish, a
transgene expressing green fluorescent protein (GFP) fused to
the C-terminal 44 amino acids of Xenopus rhodopsin
(Tam et al., 2000) under the control of the 1.3-kb proximal
Xenopus opsin promoter was inserted into the zebrafish
genome. GFP expression was easily observed in a ventral patch
of retinal cells at 4 days postfertilization (dpf). Between
45–50% of the progeny from the F1, F2, and F3 generations
expressed the transgene, consistent with a single integration
event following microinjection. Immunohistochemical analysis
demonstrated that GFP is expressed exclusively in rod
photoreceptors and not in the UV, blue, or red/green double
cones. Furthermore, GFP is localized to the rod outer segments
with little to no fluorescence in the rod inner segments, rod
cell bodies, or rod synapse regions, indicating proper targeting
and transport of the GFP fusion protein. Application of exogenous
retinoic acid (RA) increased the number of GFP-expressing cells
throughout the retina, and possibly the level of expressed
rhodopsin. When bred to a zebrafish rod degeneration mutant,
fewer GFP-expressing rods were seen in living mutants as compared
to wild-type siblings. This transgenic line will facilitate
the search for recessive and dominant mutations affecting rod
photoreceptor development and survival as well as proper rhodopsin
expression, targeting, and transport.
Perceptual classification of chromatic modulation