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Fig. 2
Spatial arrangement of cones is already patterned in the differentiating pre-column zone. (A-C) Retinal cross-section, juvenile zebrafish, Tg(trβ2: tdTomato) (red). Nuclei stained with Hoechst (gray). (A, A’) Proliferating retinal progenitors in the germinal zone (asterisks) and differentiated retina to the left: ganglion cell layer (gcl), inner nuclear layer (inl), and outer nuclear layer (onl). Immature, post-mitotic tdTomato+ Red cones (arrow) in the photoreceptor layer (onl) adjacent to Red cone progenitors (bracket) at the apical surface. (B, B’) Mitotic tdTomato+ progenitor (grey). (C, C’) Most peripheral tdTomato+ cells migrate basally toward inner retina (arrows). (D-D”’) Live-imaging 3D reconstruction of dorsal retinal margin of a trβ2: tdTomato (red);crx: mCFP (cyan);ruby juvenile fish. (See Additional file 4: Movie S2 for complete z-stack series.) (D) Single z-level focal plane (blue box); xy-crosshair is on tdTomato+ cell located in the proliferative germinal zone. (See also Additional file 4: Movie S2, white asterisks.) The flanking panels are slice views of the 3D reconstruction in the yz plane (red box), perpendicular to the retinal margin and the xz plane (green box), planar view of the retinal surface. (D’) Single, deeper z-level focal plane; xy-crosshair on a tdTomato+ immature Red cone in first cone column. In the yz plane (red box), axonal processes of immature cones separate the onl and inl (cyan, arrow). In the xz plane (green box), the xz -crosshair is on a Red cone in the first column. (D”) Higher magnification view in the xy plane of the first cone column (arrow); rounded, immature cone profiles (white dots). (See also Additional file 4: Movie S2.) (D”’) Higher magnification view in the xz plane of Red cones in first column (xz-crosshair) incorporated into the hexagonal pattern of the mature mosaic. (E-E”) Retinal flat-mount of a Tg(trβ2: tdTomato) fish (red) with anti-ZO1 (green). (E) Maximum intensity z-projection of ZO1 (green). (E’) Single z- focal plane at ZO1 level of trβ2:tdTomato label in the pre-column zone. Large immature UV cone profiles (white dots in the inset) centered in Red cone hexagons. (E”) Merged image. Scale bars: 20 μm (A’); 5 μm (B’); 10 μm (C’, D”, D”’, E”)