Fig 3

(A) Flat-mounted retina in which UV cones express a transgenic reporter (pseudo-colored magenta) under control of the UV cone opsin promoter. The dorsal side of the retina is left, ventral is right, temporal is down, and nasal is up. White lines: rows of UV cones. Yellow dots: Y-Junctions. Red dots: reverse Y-Junctions, generating row deletions. (B) Row tracing and identification of defects from retina in panel A. (C) Grain boundary from the retina in panel A. White squares indicate onset of patterning. Gray arrows indicate rotation of crystallographic orientation at the grain boundary. (D) Grain boundary presented in panel C with only the row tracing. White squares indicate onset of patterning. (E) Illustration of potential role of defect motion in generating the final spatial distribution of defects. Black region: photoreceptor epithelium. Gray region: retinal margin, where photoreceptor epithelium grows. Yellow circles: Y-Junctions. If defect motion does occur, it could allow defects to move together to form grain boundaries, as indicated by the white arrows. If defect motion is too slow, the patterning mechanism would instead have to generate grain boundaries during initial mosaic formation (not shown).