Fig. 5. Formation of the IRS in Hair-Bmpr1a KO mice and control mice. Frozen sections of hindlimb skin were prepared from control mice (A-D) and Hair-Bmpr1a KO mice (E-H) at P14. Expression of keratin 6 (A,B,E,F) in the IRS, and expression of keratin 5 (C,D,G,H) in the ORS were detected by immunofluorescence staining. B,D,F and H are merged with Hoechst (blue) for nuclear staining. Formation of IRS characterized by the expression of IRS-keratin 6 was severely reduced in Hair-Bmpr1a KO mice (E,F). (I,J) Ultrastructure of hair follicle in control mice (I) and Hair-Bmpr1a KO mice (J) at P30. Insets show keratin 5 (red) and Hoechst (blue) signals at P30. Absence of IRS cells resulted in proliferation of keratin-5-positive ORS cells. c, cortex; ci, cuticle of IRS; he, Henle's layer; hu, Huxley's layer; irs, inner root sheath; me, medulla; ors, outer root sheath; th, trichohyalin granule. Scale bars: 100 µm in A-H and insets in I,J; 5 µm in I,J.