Figure 3: Soluble RA levels are higher in the distal half of the BPs at E10.

Bright-field images of LacZ expression in RA reporter cells (F9-RARE-LacZ) that were co-cultured with proximal (a) and distal halves (b) from the same E10 BP. Many cells in the vicinity of the distal samples were positive for the blue LacZ signal while few in the vicinity of the proximal sample were. (c) E10 retinal tissue was used as a tissue control. (d) As pharmacological controls, reporter cells in separate wells were exposed to 0 nM, 5 nM and 100 nM RA. Scale bar, 1 mm.