018 Targeted Disruption of LIG-1 Gene Provides New Insight into Keratinocyte Stem Cells.

H. Miura1, Y. Suzuki2, K. Kobayashi3, G. Kondoh4, S. Sano1, K. Ozawa1, S. Inui1, A. Nakata2, T. Takagi2, M. Tohyama5, K. Yoshikawa1 and S. Itami1. 1Department of Dermatology, 4Department of Social and Environmental Medicine, 5Department of Anatomy and Neuroscience, Graduate School of Medicine, Osaka University, Osaka, Japan, 2Read generation Laboratory, 3Safety Research Laboratory, Tanabe Seiyaku Co. Ltd., Osaka, Japan.

Epidermis that covers the skin surface is continuously regenerated throughout the lifetime of the mammalian adult through proliferation of keratinocyte stem cells. While keratinocyte stem cells play a central role in tissue homeostasis, wound healing, cancers, and skin-based gene therapy, the precise in vivo localization of the cells is not yet settled because of the scarcity of appropriate molecular markers. LIG-1, a transmembrane glycoprotein of which extracellular region is uniquely organized with the leucine-rich repeats and immunoglobulin-like domains, is expressed predominantly in the brain. Here we show that the cutaneous expression of LIG-1 was restricted to the cells in the bulge of hair follicles and the subpopulation of epidermal basal cells that were considered to be the keratinocyt stem cells in mice and human. About 40 % of á6-integrin positive rapidly adherent keratinocytes that were enriched in keratinocyte stem cells strongly expressed LIG-1 on their cell-surface. To clarify the physiological roles of LIG-1 in vivo, we disrupted the gene in mice by gene targeting. The LIG-1 deficient mice developed a skin change on their tail and facial area after birth. The affected skins were histologically characterized by epidermal hyperplasia, hyperkeratosis with parakeratosis, neutrophil influx, and the subcorneal pustules similar to Munro’s microabscesses. The keratinocytes in the lesion were highly proliferative with perturbed terminal differentiation. Therefore, we infer that LIG-1 is a new cell-surface marker for keratinocyte stem cells and regulates the growth and differentiation of keratinocyte stem cells.