Fig. 5. The Mitf^mi-rw allele allows for the expression of Mitf and its target gene tyrosinase in the anterior RPE as well as for residual pigmentation in the iris but leads to an abnormal RPE dorsally. Sections of wild-type (wt) and Mitf^mi-rw/mi-rw mutant mouse eyes of the indicated ages were stained with a pan-Mitf in situ probe (A,B,E,F), a pan-MITF antiserum (C,D,G,H), antibodies against tyrosinase (I-L), or against PAX6 (green) and TUJ1 (red) (Q-T). Note that the mutant eye expresses Mitf RNA (B,F) and low levels of MITF protein, along with tyrosinase, particularly at later stages (compare G with H, arrows; K with L). Also note that in the mutant at E17.5, the distal ciliary margin, although positive for Mitf RNA (F), is relatively free of MITF and tyrosinase (arrowhead in H and L, compare with arrowhead in G and K). (M,N) Strong pigmentation at P0 in wild type (M) and weak pigmentation in rw (N). (O,P) Pigmentation in adult wild-type iris (O) and rw iris (P). (Q,R) Dorsal thickening of the E12.5 RPE in rw (R) compared with wild type (Q). (S,T) RPE abnormalities in rw at E17.5. Arrowheads in S mark the location of the wild-type RPE, which now is free of PAX6 staining. By contrast, mutant RPE retains PAX6 staining and in this eye showed epihelial folds rather than homogeneous thickening (arrowhead in T).