To further analyze the expression of
capn5a/b in the adult zebrafish retina, we performed FISH with
capn5a/b probes on sections of adult WT zebrafish retina. Expression of
capn5a and
capn5b was again observed in the photoreceptor inner segments (
Fig. 3). The rod and cone photoreceptors in the adult zebrafish retina are highly tiered and morphologically distinguishable, such that (moving from the vitreal to scleral direction) the round rod nuclei are located most proximal to the OPL, followed by the UV and blue cones, then the ellipsoid red/green double cone nuclei interspersed with rod inner segments, the red/green cone outer segments, and finally the rod outer segments located most proximal to the RPE.
29 Interestingly, the FISH expression pattern for
capn5a/b appeared to localize primarily to the cone, but not rod inner segments. To determine whether this was the case, we used the TαC-GFP transgenic line, in which green fluorescent protein (GFP) is expressed specifically in the cones,
28,43 and performed FISH for
capn5a in combination with IHC for GFP. We observed extensive colocalization of GFP and
capn5a expression (
Figs. 3D–D″). We then performed the same experiment using the XOPS:GFP transgenic line, which expresses GFP specifically in the rods.
29 We did not observe any colocalization of the rod GFP signal and
capn5a expression (
Figs. 3E–E″), which we confirmed using confocal microscopy (
Figs. 3F–F″).
Capn5b displayed the same colocalization pattern as
capn5a (not shown). We confirmed the expression of Capn5 protein in the adult retina using the CAPN5 antibody (
Figs. 3C–C″). Capn5 expression was observed in the cone inner segments, outer segments, and in the synaptic terminals of the adult retina. Taken together, these results suggest that, similar to mammals, zebrafish Capn5 is expressed in retinal photoreceptors. However, zebrafish Capn5 expression appears to be cone-specific, which has not been reported for CAPN5 in the mammalian retina.