Fig 1: The pigment cells of the Fz5 mutant vitreous are melanocytes. (A–N) P3 retinal sections. (A–D), Sox10 is in red, and Tyrp1 is in green. (A–D) Co-labeling of neural crest marker Sox10 and melanin biosynthetic enzyme Tryp1. Boxed areas (A) and (B) are magnified in (C) and (D), respectively. (C) Wild-type vitreous showed background staining in hyaloid vessels. (D) Intense Tyrp1 cytoplasmic staining colocalized with Sox10-positive cells of the vitreous mass. (E, F) Bright-field microscopy of the same sections of (A, B). Boxed areas are pigmentary regimental mass (M) and choroid melanocytes and RPE (N), respectively, which are magnified in (M) and (N). (G–J) Pax3 is in red, and Tyrp1 is in green. Boxed areas in (G) and (H) are magnified in (I) and (J) respectively. (I) Pax3 expression is detected in endothelial cells. Note that the Tryp1 staining is considered background. (J) Strong Tyrp1 cytoplasmic staining appeared inversely correlated with the Pax3 intensity (arrows). (K, L) Bright-field microscopy of the same sections (G, H). The arrow in (L) points to the regimental mass. (M) High magnification of vitreous pigmentary cells. (N) High magnification of RPE and choroid melanocytes. The red arrow points to RPE, and the black arrow point to choroid melanocytes. (O, P) Transmission electron microscopy of P60 mutant vitreous (O) and RPE and choroid (P).