Figure 2

Zebrafish Nrl is Conserved and Sufficient to Induce Rod Photoreceptors in Zebrafish

(A) Wild-type zebrafish larval retina in en face view has a dense forest of UV cone photoreceptor cells (magenta) and fewer rod cells (green) scattered throughout. (A’) Ectopic expression of zebrafish Nrl in differentiating UV cones transmutes these cells to a rod cell fate as determined by 4C12 immunoreactivity (green; 4 days postfertilization [dpf] larva). Inset: UV cones (magenta) are 4C12+ (green).

(B) Rods are more abundant in wild-type zebrafish by 6dpf. (B”) Expression of mouse Nrl reroutes cones to a rod cell fate (defined as GFP + cells in Tg[rh1:gfp]) in a manner indistinguishable from zebrafish Nrl (B′). Note the increase in GFP-positive rods apparent in both lines (B′ & B″) relative to wild-type retina.

(C) Cellular morphology of UV cones vs. rods (C vs. C′) is readily distinguishable by 7dpf in photoreceptor cells expressing GFP. (C″) Ectopic expression of zebrafish Nrl causes UV cones to take on a rod-like cell morphology. Larvae in (C″) are on a nrl^−/− null background (and thus lack native rod cells, described in Figure 3) to ensure the source of GFP-positive rod-like cells visualized here is the UV cones ectopically expressing the transgenic Nrl.