Fig. 4. Hair shaft production is severely impaired in Catnb^ex3K14/+ skin. (A,B) Advancing hair development was examined by transplanting back skin from E17 embryos to nude mice. After 5 weeks, dense hair was present in control graft, whereas the Catnb^ex3K14/+ mutant graft had produced only a few hairs. (C-F) Light microscopic examination revealed no major differences in hair structure between control and mutant grafts. Arrows indicate zig-zags and arrowheads indicate awl hairs (C,E). High-magnification pictures (D,F) show internal structure of awl hairs. (G-N) Histological analysis of control (G,I) and mutant (H-N) grafts after 3 (G,H,K,L) or 5 weeks (I,J,M,N). Control skin showed regular row of catagen (G) and anagen-stage hair follicles (I), but in the mutant graft only few well-developed follicles were observed (arrows in H and J). In the mutant skin grafts, the down-growth of hair follicles was dramatically impaired and a variety of abnormalities were obvious (K-N): extra sebocytes in large clusters (arrows in K and L), epithelial budding from the outer root sheath of aberrant follicles (arrows in M) and large epithelial cysts filled with keratin-like material (arrowheads in J,L,N). Scale bars: 2 mm in A; 200 µm in C,E,G,I; 100 µm in D,F,L-N; 50 µm in K.