Fig. 5. Histological analyses of the hair cycle. Skin sections from mice stained with hematoxylin and eosin were analyzed at days 0-21. (A) Wild-type (WT) tissues at day 15 displayed hair morphology typical of the late postnatal hair follicle morphogenesis phase, with well-differentiated hair follicles characterized by large oval hair bulbs surrounding the dermal papillae (arrow). At the same day after birth, the ECR3E-Myc transgenic follicles had already entered the catagen phase as evidenced by the regressing follicles with the papilla outside of the hair bulb (arrow). (B) The control ECR3E-1-2-Myc skin had a hair cycle similar to that of the wild-type skin as illustrated by the fact that the hair was in late postnatal hair follicle morphogenesis phase at day 15 and was not distinguishable from wild-type follicles of the same age.