Fig. 3. Abnormal hair follicle formation in Hair-Bmpr1a KO mice. Hematoxylin-Eosin (HE)-stained sections of hindlimbs from Hair-Bmpr1a KO mice are shown in the developmental stage of HF. First anagen phase of P14 control mice (A). Hair follicles in the control skin retract into dermis, maintaining close contact between the dermal papilla and the epithelial hair shaft in P14 control mice (arrow). Abnormally differentiated hair shafts were observed in P14 Hair-Bmpr1a KO mice (B-D). Retracting epithelial hair shafts that separate from the dermal papilla and form cysts in hair canals were observed in P14 Hair-Bmpr1a KO mice (arrow, B). Section from P30 control mice shows second anagen phase of HF (E). In P30 Hair-Bmpr1a KO mice (F-H), nearly all of the canals have small cysts (arrowhead, H) in the HF. Section from older (10-month-old) control mice was processed with HE staining (I). The hair canals were wider and large cysts (arrowhead) were observed in hair canals in older Hair-Bmpr1a KO mice (J-L). The number of HFs per mm² was counted in P14, P30 and mature mice (n=7 per group) (M). Data are given as mean±s.e.m.; * P<0.05; **P<0.01; Student's t-test. d, dermis; s, subcutis; pc, panniculus carnosus. Scale bars: 100 µm in A,B,E,F,I,J; 50 µm in C,D,G,H,K,L.