Identification of novel telogen markers underscores that telogen is far from a quiescent hair cycle phase Mikhail Geyfman 1,* , William Gordon 1,2,* , Ralf Paus 3 , and Bogi Andersen 1,2 1 Departments of Medicine and Biological Chemistry, University of California, Irvine 2 Center for Complex Biological Systems, University of California, Irvine 3 Department of Dermatology, University of Lübeck, Lübeck, Germany & School of Translational Medicine, University of Manchester, Manchester, UK To the Editor In contrast to the dynamic and striking changes in hair follicle (HF) morphology during the anagen and catagen phases of the hair cycle, the telogen follicle appears static. However, it has been argued that the quiescent appearance of telogen HFs is deceptive (Davis 1962, Stenn, Paus 2001, Higgins, Westgate 2009). For example, the expression of some genes clearly peaks during telogen (Greco, Chen et al. 2009). Also, functionally distinct sub- phases of telogen have been identified (“competent” versus “refractory telogen”) based on the ability to initiate anagen after plucking (Plikus, Mayer et al. 2008). To gain further insights into the biological activities of telogen and to further probe the concept that telogen represents an important hair cycle-regulatory phase, we profiled skin mRNA expression patterns in mid (P54) and late (P59) second telogen in C57BL6 male mice with highly synchronized HF cycling. This data was analyzed in combination with previously published hair cycle gene expression profiling data that included an early telogen sample (P44) (Lin, Kumar et al. 2009). Microarray hybridization and data analyses are described in Supplementary Methods online. As RNA was prepared from whole skin, subtle transcriptional changes occurring in a small population of follicular cells may not be detected and opposite changes in different cell populations may cancel each other. Also, skin samples used in our study contain subcutaneous adipose tissue, recently identified as critical for extrinsic modulation of hair follicle behavior (Plikus, Baker et al. 2011, Festa, Fretz et al. 2011). While many genes reach their highest or lowest expression in telogen skin, we defined the telogen gene expression signature more rigorously as genes with expression 1.5-fold higher Users may view, print, copy, and download text and data-mine the content in such documents, for the purposes of academic research, subject always to the full Conditions of use:http://www.nature.com/authors/editorial_policies/license.html#terms Correspondence: Bogi Andersen, Sprague Hall, Room 206, University of California, Irvine, Irvine, CA 92697, Phone: 949-824-9093, bogi@uci.edu. * Equal authorship contribution Conflict of Interest: The authors state no conflict of interest HHS Public Access Author manuscript J Invest Dermatol. Author manuscript; available in PMC 2012 September 01. Published in final edited form as: J Invest Dermatol. 2012 March ; 132(3 0 1): 721–724. doi:10.1038/jid.2011.367. Author Manuscript Author Manuscript Author Manuscript Author Manuscript