Defective melanosomes in homozygous cappuccino mice.

(A) A cno/cno mouse (foreground) and a normal littermate. Note marked coat-color dilution in the mutant. (B, C) Plastic embedded light microscopy images of normal (panel B) andcno/cno (panel C) eyes showing the profound reduction in the choroid layer (asterisk) characteristic of cno homozygotes. Other layers are normal. (Note: The photoreceptor and outer-segments layers are missing in the C3H/HeJ strain.) (D) Electron photomicrograph of a normal (+/cno) eye with the retinal pigmented epithelial (PE) layer toward the top and the choroid (CH) below. CC, chorio-capillaries. (E) cno/cnoretinal PE layer. Note severe reduction in number and size of the melanosomes (arrows). (F) cno/cno choroid layer at higher magnification showing small, incompletely melanized melanosomes (arrows). Bars, 10 μm (B-C), 1 μm (D-F).