Fig. 7. Abnormal follicular cycling and proliferation in epithelial Bmpr1a mutants. (A-F,G,H) Histology of dorsal skin from K14-Cre40; Bmpr1a^cl/+ control littermates (A,E,G) and K14-Cre40; Bmpr1a^cl/cl mutants (B,F,H), and ventral skin from bcre-32; Bmpr1a^cl/+ control littermate (C) and bcre-32; Bmpr1a^cl/null mutant (D) at P12 (A,B), P17 (C,D), P21 (E,F) and P34 (G,H). Control skin progresses through anagen (A), catagen (C), telogen (E) and first postnatal anagen (G), but mutant skin remains in an abnormal anagen-like state. Arrow in B indicates misshapen, expanded dermal papilla; arrow in F indicates abnormal, undifferentiated cells in the center of a mutant follicle. (E',F') Alkaline phosphatase staining of skin sections from the samples shown in E and F, revealing locations of dermal papillae (DP; blue arrows). Red arrow (F') indicates a pigmented cast being extruded to the epidermis. (E'',F'') Anti-BrdU staining of skin sections from the samples shown in E and F, revealing continued proliferation of mutant follicles (arrow in F''). (G',H') Anti-BrdU staining of sections from the samples shown in G and H, showing proliferation in the bulbs of control anagen follicles (G'; yellow arrow), and in the bulbs and outer root sheaths (yellow arrows), and epidermis (white arrow) of mutant skin (H'). Scale bars: in F' applies to A-F'; in F'' applies to E'',F''; in H applies to G,H; in H' applies to G',H'. SG, sebaceous gland.