title: A Guide to Studying Human Hair Follicle Cycling In Vivo.
abstract: Hair follicles (HFs) undergo lifelong cyclical transformations, progressing through stages of rapid growth (anagen), regression (catagen), and relative "quiescence" (telogen). Given that HF cycling abnormalities underlie many human hair growth disorders, the accurate classification of individual cycle stages within skin biopsies is clinically important and essential for hair research. For preclinical human hair research purposes, human scalp skin can be xenografted onto immunocompromised mice to study human HF cycling and manipulate long-lasting anagen in vivo. Although available for mice, a comprehensive guide on how to recognize different human hair cycle stages in vivo is lacking. In this article, we present such a guide, which uses objective, well-defined, and reproducible criteria, and integrates simple morphological indicators with advanced, (immuno)-histochemical markers. This guide also characterizes human HF cycling in xenografts and highlights the utility of this model for in vivo hair research. Detailed schematic drawings and representative micrographs provide examples of how best to identify human HF stages, even in suboptimally sectioned tissue, and practical recommendations are given for designing human-on-mouse hair cycle experiments. Thus, this guide seeks to offer a benchmark for human hair cycle stage classification, for both hair research experts and newcomers to the field.
authors.affiliation: Hair Transplantation Center, Kyungpook National University Hospital, Daegu, Korea; Department of Immunology, Kyungpook National University School of Medicine, Daegu, Korea; Department of Developmental and Cell Biology, University of California, Irvine, Irvine, California, USA; Sue and Bill Gross Stem Cell Research Center, University of California, Irvine, Irvine, California, USA; Center for Complex Biological Systems, University of California, Irvine, Irvine, California, USA.
authors.forename: Ji Won
authors.initials: JW
authors.lastname: Oh
authors.affiliation: Department of Dermatology, University of Lübeck, Lübeck, Germany.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Kloepper
authors.affiliation: Department of Dermatology, University of Lübeck, Lübeck, Germany; Comprehensive Centre for Inflammation Research, University of Lübeck, Germany.
authors.forename: Ewan A
authors.initials: EA
authors.lastname: Langan
authors.affiliation: Division of Molecular Pathology, the Netherlands Cancer Institute, Amsterdam, the Netherlands.
authors.forename: Yongsoo
authors.initials: Y
authors.lastname: Kim
authors.affiliation: Institute for Computational and Mathematical Engineering, Stanford University, Stanford, California, USA.
authors.forename: Joongyeub
authors.initials: J
authors.lastname: Yeo
authors.affiliation: Department of Dermatology, Kyungpook National University School of Medicine, Daegu, Korea.
authors.forename: Min Ji
authors.initials: MJ
authors.lastname: Kim
authors.affiliation: Department of Developmental and Cell Biology, University of California, Irvine, Irvine, California, USA; Sue and Bill Gross Stem Cell Research Center, University of California, Irvine, Irvine, California, USA; Center for Complex Biological Systems, University of California, Irvine, Irvine, California, USA.
authors.forename: Tsai-Ching
authors.initials: TC
authors.lastname: Hsi
authors.affiliation: Dermatohistologisches Labor Rose/Bartsch, Lübeck, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Rose
authors.affiliation: Department of Pathology, Kyungpook National University School of Medicine, Daegu, Korea.
authors.forename: Ghil Suk
authors.initials: GS
authors.lastname: Yoon
authors.affiliation: Department of Dermatology, Kyungpook National University School of Medicine, Daegu, Korea.
authors.forename: Seok-Jong
authors.initials: SJ
authors.lastname: Lee
authors.affiliation: Department of Dermatology, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
authors.forename: John
authors.initials: J
authors.lastname: Seykora
authors.affiliation: Hair Transplantation Center, Kyungpook National University Hospital, Daegu, Korea; Department of Immunology, Kyungpook National University School of Medicine, Daegu, Korea.
authors.forename: Jung Chul
authors.initials: JC
authors.lastname: Kim
authors.affiliation: Department of Immunology, Kyungpook National University School of Medicine, Daegu, Korea.
authors.forename: Young Kwan
authors.initials: YK
authors.lastname: Sung
authors.affiliation: Hair Transplantation Center, Kyungpook National University Hospital, Daegu, Korea; Department of Immunology, Kyungpook National University School of Medicine, Daegu, Korea. Electronic address: moonkim@knu.ac.kr.
authors.forename: Moonkyu
authors.initials: M
authors.lastname: Kim
authors.affiliation: Dermatology Research Centre, Institute of Inflammation and Repair, University of Manchester, Manchester, UK; Department of Dermatology, University of Münster, Münster, Germany. Electronic address: ralf.paus@manchester.ac.uk.
authors.forename: Ralf
authors.initials: R
authors.lastname: Paus
authors.affiliation: Department of Developmental and Cell Biology, University of California, Irvine, Irvine, California, USA; Sue and Bill Gross Stem Cell Research Center, University of California, Irvine, Irvine, California, USA; Center for Complex Biological Systems, University of California, Irvine, Irvine, California, USA. Electronic address: plikus@uci.edu.
authors.forename: Maksim V
authors.initials: MV
authors.lastname: Plikus
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000502:physiology; D001707:Biopsy, Needle; D002453:Cell Cycle / Q000502:physiology*; D002478:Cells, Cultured; D017408:Guidelines as Topic; D006197:Hair / Q000502:physiology*; D018859:Hair Follicle / Q000033:anatomy & histology / Q000254:growth & development*; D064593:Heterografts; D006801:Humans; D007150:Immunohistochemistry; D051379:Mice; D016513:Mice, SCID