<i>In situ</i> hybridization of <i>KRT75</i> in embryonic and adult feather filaments.

<p>(A) Cross section of E13 feather filaments. <i>KRT75</i> is expressed in the region that is destined to become the ramus. Note that embryonic downy feathers do not have a rachis. (B) <i>KRT75</i> is expressed in the rachis and ramus in adult normal regenerating feathers. (C) <i>KRT75</i> is expressed in the rachis and ramus in adult frizzle regenerating feathers. (D) A nearly mature rachis expresses <i>KRT75</i> in the ventral part of the rachis. In comparison, feather keratin is expressed in the dorsal part of the rachis. (E) Sections of a rachis from adult wing feathers at different levels of maturity from the feather base (immature) to the feather tip (mature). <i>KRT75</i> is expressed in the ventral part of the rachis. In comparison, feather keratin is expressed in the distal part of the rachis. (F) Schematic drawing which summarizes the expression pattern of <i>KRT75</i> and feather keratin adult feather rachis. (G) Barb ridge of adult wing feathers at different levels of maturity. <i>KRT75</i> is expressed in the ventral part of the ramus. In comparison, feather keratin is expressed in the distal part of the rachis. (H) Schematic drawing which summarizes the expression pattern of <i>KRT75</i> and feather keratin in adult feather ramus. (I) Double immunostaining for K75 (green) and feather keratin (red) in the rachis of normal and frizzle feathers. The yellow dotted line outlines the rachis and the white dotted line indicates the medulla. D, dorsal; V, ventral; bb, barbule; rc, rachis; rm, ramus.