1. ^*Pathology Department, Beth Israel Deaconess Medical Center, Boston, Massachusetts, USA
2. ^†Departments of Cancer Biology and Pathology, University of Massachusetts Medical School, Worcester, Massachusetts, USA

Correspondence: Stephen Lyle, MD, PhD, UMass Medical School, Lazare Research Building, Worcester, Massachusetts 01605, USA. Email: stephen.lyle@umassmed.edu

Received 3 April 2005; Revised 6 July 2005; Accepted 22 July 2005; Published online 15 November 2005.

Abstract

Epithelial stem cells within the human hair follicle are critical for hair development, hair cycling, wound healing, and tumorigenesis. We and others have previously shown that the hair follicle bulge area contains keratinocyte stem cells, whereas the hair matrix represents the proliferating and differentiating transit-amplifying (TA) cell compartment. In order to better characterize the phenotypic differences between human keratinocyte stem cells and their daughter TA cells, we compared the in vitro properties of cell adhesion, cell migration, clonogenicity, and in vitro life span. Epithelial outgrowths from the hair matrix appeared within 2 d of explant, whereas stem cell outgrowths appeared between 7 and 10 d after explant. Both populations form colonies; however, stem cells from telogen follicles formed more total colonies, and more colonies greater than 3 mm. Upon subculture, stem cells formed colonies until passage 6 and terminally differentiated at passage 7, whereas TA cells only formed colonies until passage 2. Stem cells express more 1 integrin and adhere more rapidly to collagen IV. Most strikingly, TA cells showed a 7-fold greater mobility on migration assays than stem cells (0.704 vs 0.102 m per min). These results help define the human hair follicle stem cell and TA cell phenotypes and correlate with the in vivo properties of these compartments.