Talveen S Purba, Lars Brunken, Nathan J Hawkshaw, Michael Peake, Jonathan Hardman, Ralf Paus

The cell cycle is of major importance to human hair follicle (HF) biology. Not only is continuously active cell cycling required to facilitate healthy hair growth in anagen VI HFs, but perturbations in the cell cycle are likely to be of significance in HF pathology (i.e. in scarring, non-scarring, chemotherapy induced and androgenic alopecias). However cell cycle dynamics of the human hair follicle (HF) are poorly understood in contrast to what is known in mouse. The aims of this method review are two fold; principally to address this gap we present a primer to introduce histological techniques to study the cell cycle in the human HF whilst concurrently encouraging the exploitation of the human HF as a powerful and clinically relevant tool to investigate mammalian cell cycle biology in situ. To achieve this we describe methods to study general 'proliferation' (nuclei count, Ki-67 expression), apoptosis (terminal deoxynucleotidyl transferase dUTP nick end labelling, cleaved caspase 3), mitosis (phospho- histone H3, 'pS780'), DNA synthesis (5-ethynyl-2'-deoxyuridine) and cell cycle regulation (Cyclins) in the human HF, whilst also providing specific examples of dual labelling to further provide instructive cell cycle analyses or to investigate the cell cycle behaviours of specific HF keratinocyte sub-populations (i.e. Keratin 15+ stem / progenitor cells). This article is protected by copyright. All rights reserved.