1°NC cells cover the proximal but not the distal side of the optic cup.

(A-C’) 3D rendered images of a Tg(sox10:mem-tdEosFP) embryo are shown from three different angles: dorsal views (A-A’), lateral views (B-B’) and ventral views (C-C’). Anterior, left. Two selected time points (A-C: 15 hpf; A’-C’: 18 hpf) are shown. The grey spheroid represents the optic cup (OC). One side of the eye (rectangular region) in the dorsal view (A-A’) is highlighted in lateral (B-B’) and ventral views (C-C’). (A-C) At 15 hpf, 1°NC cells start covering the optic cup from its posterior end and its proximal side (arrowheads, A). Only a small dorsal portion of the eye is covered by 1°NC cells (arrowheads in B, arrow in C), while the ventral half of the eye is not covered with 1°NC cells (C). The arrow in C points at 1°NC cells on the dorsal side of the eye. (A’-C’) By 18 hpf, 1°NC cells have reached the rostral end of the optic cup (arrowhead in A’), with the proximal side of the eye covered roughly halfway (arrows in B’ and arrowheads in C’). Importantly, 1°NC cells exclusively migrate over the proximal side of the eye (arrows, B’) and do not migrate over the lens side (distal side; arrowheads, B’). Note that 2°NC cells in clusters (asterisks in A’) have not yet reached the eye at 18 hpf. (D-F) Ultrastructure of 1°NC cells (magenta). (D) 1°NC cells are located on the proximal side of the optic cup (blue; transverse view at 18 hpf). The regions indicated by squares are shown in E and F. Black honey comb pattern is from the grid. (E) 1°NC cells form a mono-layered sheet. (F) A 1°NC cell (coloured in magenta) show a large cell-cell contact plane with neighbouring 1°NC cells. OSE: optic surface epithelium; Br: brain. (PDF)