Fig. 5. Cochlear hair cells degenerate rapidly in Gfi1 mutants. Math1/ß-Gal expression (blue) and hair cell placement are visualized by the ß-galactosidase cassette driven by the Math1 promoter in whole mounts of the cochlea. (A,C,E,I) Gfi1 wild type (+/+). (B,D,F-H,J-L) are Gfi1 null (-/-). (A,B) Math1/ß-galactosidase at E15.5. (A) Gfi1 wild-type (+/+) region of the basal cochlea, showing the development of the orderly arrangement of three outer and one inner row of hair cells. (B) Gfi1 null (-/-) basal cochlea showing Math1 expression and hence specification of hair cells is unaffected in the null cochlea. However, the characteristic rows of inner and outer hair cells are not as clearly defined as in wild type. (C,D) Math1/ß-Gal expression at E17.5. (C) Gfi1 wild-type region of the basal cochlea showing the orderly arrangement of three outer and one inner row of hair cells. In the wild-type mouse, these orderly rows are continuous along the entire length of the cochlea. (D) Gfi1-null basal cochlea showing persistent disorganization of hair cells and decreased hair cell numbers. (E-H) Math1/ß-galactosidase at P0. (E) Gfi1 wild-type region of the basal cochlea showing the orderly arrangement of three outer and one inner row of hair cells. (F) Gfi1 null basal cochlea, (G) Gfi1 null medial cochlea, (H) Gfi1 null apical cochlea. Note the degeneration of the cochlea in a basal to apical gradient. (I-L) Math1/ß-galactosidase at P3. (I) Gfi1 wild-type region of the basal cochlea showing the orderly arrangement of three outer and one inner row of hair cells. (J) Gfi1 null basal cochlea; (K) Gfi1 null medial cochlea; (L) Gfi1 null apical cochlea. Note the degeneration of the cochlea in a basal to apical gradient.

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