Fig. 4

Production of pure L cones is regulated by trβ2 expression in cone precursors. (A) L-opsin–expressing cone numbers are diminished, whereas UV-opsin–expressing cone numbers are increased in animals injected with trβ2 morpholino (MO). L-opsin expression is rescued in the morphant when trβ2 is constitutively active under the crx or gnat2 promoters in the stable transgenic lines. Images were acquired at 5 dpf. (B) Quantification of the density of cones expressing each opsin type for the conditions in A (mean ± SEM). Numbers in parentheses indicate number of eyes. Significant differences are noted by asterisks (*P < 0.001); for each cone type, comparisons were made between trβ2 MO and the GeneTools standard control MO (Std MO) and between trβ2 MO and crx:trβ2/ trβ2 MO or gnat2:trβ2/ trβ2 MO. There was no significant difference in total photoreceptor density among Std MO (mean ± SEM in 100 μm², 18.6 ± 0.3; n = 9 eyes), trβ2 MO (18.9 ± 0.2; n = 7), and gnat2:trβ2/ trβ2 MO (19.1 ± 0.3; n = 7). However, compared with the trβ2 MO, the density of photoreceptors in crx:trβ2/ trβ2 MO was increased (21.6 ± 0.7; n = 6; P = 0.005). (C) Double immunostaining for L-opsin and M-, S-, or UV-opsin in 5 dpf Tg(gnat2:MYFP-2A-trβ2) fish injected with trβ2 MO. Examples of cones expressing L-opsin and M- or UV-opsin are indicated by arrowheads. (D) Quantification of the proportion of each cone type that also expressed L-opsin (mean ± SEM). For example, (M + L)/M is the proportion of M cones coexpressing L-opsin. Numbers in parentheses indicate number of eyes.