Fig 2: Kcne2 expression in the OPL of the mouse retina. Cross-sections from mouse retina double labeled with Kcne2 (red) and the presynaptic marker Snap25 (A–D, green), the cone marker cone-arrestin (E–H, green), peanut agglutinin labeling cone pedicles (I–L, green), and the rod bipolar cell (rod-BC) marker PKCa (M–S, green). Overview images of the entire retinal cross-section are shown in (A), (E), (I), and (M). Data show that Kcne2 co-localizes with Snap25 in the outer portion of the OPL (A–D). A portion of this Kcne2 immunoreactivity was localized at the distal surface of the cone pedicles (E–L, white arrows). In addition U-shaped Kcne2-immunopositive structures were observed (white circles) that showed spatial association with dendritic terminals of rod-BCs (M–S). A subset of bipolar cells with somata that are positive for Kcne2 but negative for PKCa (N, O, Q, R, asterisks) can also be observed. Note that immunostaining against PKCa was performed with two different antibodies, one risen in rabbit (M–P) and one risen in mouse (Q–S). GCL, ganglion cell layer; IPL, inner plexiform layer. Scale bar: 10 µm.

Fig 3: Kcne2 immunoreactivity in the soma of cone ON-BCs. Cross-sections from mouse retinae double labeled with Kcne2 (red) and the cone marker Chx10 (A–D, green). Cells immunopositive for Kcne2 in the membrane around the soma are primarily located at the outer portion of the INL and are also weakly positive for Chx10. GCL, ganglion cell layer; IPL, inner plexiform layer. Scale bar: 10 µm.

Fig 4: Kcne2 expression in the OPL is conserved among vertebrates. (A) Phylogenetic tree for the five vertebrate species included in this study spanning 435 million years of evolution. Note that the zebrafish (Danio rerio) is shown in gray to highlight the relatively low sequence homology of its closest relative to Kcne2 (Kcne2-like protein) to the antigen epitope used to raise the Kcne2 antibody. (B–E) Immunohistochemistry performed on retinal cross-sections consistently shows immunoreactivity for Kcne2 (red) in the OPL of all studied species. In the Argentinian cowbird (Molothrus rufoaxillaris), immunoreactivity can also be observed in the IS/OS layer. Note that data from the mouse are shown in Figure 1. GCL, ganglion cell layer; IPL, inner plexiform layer. Scale bar: 10 µm.

Fig 5: Kcne2 expression in cone inner segments of the mouse retina. Cross-sections from mouse retinae double labeled with Kcne2 (red) and the cone marker cone arrestin (A–D, green). Overview images of the entire retinal cross-section are shown in the left column (A). Kcne2 immunoreactivity was seen in cone photoreceptor inner segments. Rod inner segments exhibited an unspecific fluorescence mostly not above levels of fluorescence commonly observed in this layer plus some punctate signal unrelated to any anatomical structure, conceivably minor unspecific binding of the antibody employed. GCL, ganglion cell layer; IPL, inner plexiform layer. Scale bar: 10 µm.