B5.3 Epithelial-Mesenchymal Regulation of Feather Follikular Stem Cells

Cheng-Ming Chuong, Zhicao Yue

Department of Pathology, Keck School of Medicine, University of Southern California, Los Angeles, CA 90033

Development and regeneration of skin appendages depend on interactions between epithelia and mesenchyma. During development, the location and phenotype of feathers are determined by the mesenchyme, while the orientation is determined by the epithelium. In adult, both hairs and feathers show robust regenerative ability. While stem cells in hair follicles have been studied, none has been carried out in the feather - and feathers do not have bulge region in ORS. Where could the stem cells be? Here we identify a novel "collar bulge" region in the proximal follicle that contains skin stem cells as judged by slow cycle labeling, DiI tracing and chicken/quail transplantation. Cell kinetics and molecular expression change dynamically during the growth, resting, and initiation phases of the feather cycle. Following plucking, cell flux reverses and follicle sheath epithelia migrate back into the follicle to repopulate the stem cell niche. Perturbations of signaling molecules in the follicular micro-environment alter the fates of epidermal stem cells. Thus the status of feather epithelia is actively regulated by epithelial-mesenchymal interactions in the micro-niche of proximal follicles during molting and regeneration.