Figure 12. The rSC begins to express Prox1 and to acquire a tube-like morphology.

Z-projection of confocal stacks encompassing the rSC from a Prox1-GFP eye at P4.5. VECAD immunostaining shows a region with branching of the rudimentary vessel (block arrows, equivalent to stage D in Figure 11). Prox1 is first expressed in the rSC at late P4. The branching rSC begins to acquire Prox1 expression as indicated by GFP⁺ cells (arrowhead). Higher Prox1 expression correlates with transition of rSC morphology from a sprouting chain of cells to a flattened tube (arrows). (Inset) DIC merged image showing that the tubular regions of the rSC have pockets of space filled with RBCs (black arrows). Scale bar, 50 µm.