Fig. 2. Expression of keratin 5, trychohyalin and acidic hair keratins in transgenic and wild-type hair follicles. Frozen sections were prepared from wild-type (A and C) and transgenic (B and D) P12 dorsal skin and assayed by indirect immunofluorescence staining for the expression of keratin 5 (MK5, red) in the ORS, and trychohyalin (AE15, green) in the IRS and medulla (A and B), or acidic hair keratins (AE13, green) in the cortex and cuticle (C and D). Keratin 5 expression in the ORS is normal in Msx2–Noggin hair follicles. Trychohyalin is present in the IRS, but absent from the center of the transgenic hair follicles, where the medulla should have formed (arrowhead in B). Expression of acidic hair keratins in the cortex and cuticle is completely lost in the transgenic hair follicles (D).