C2   HISTOLOGY OF THE MURINE HAIR CYCLE

¹Paus R., ²Müller-Röver S. ¹Dept. of Dermatology, University Hospital Eppendorf, University of Hamburg, Hamburg, Germany; ²Dept. of Dermatology, St. Bartholomew’s and the London Royal School of Medicine and Dentistry, Queen Mary and Westfield College, London, UK

Numerous strains of mice with defined mutations display pronounced alterations of hair follicle cycling,  even in the absence of macroscopical abnormalities of the hair phenotype. In order to recognise even subtle, hair cycle-related abnormalities in such mouse mutants, and in order to evaluate discrete effects of hair growth-modulating agents in the murine system, it is critically important to be able to accurately determine and classify all the substages of the normal murine hair cycle. In this course, we present pragmatic basic and auxiliary criteria for identifying key stages of hair follicle growth (anagen), regression (catagen) and quiescence (telogen) in C57BL/6 mice. For each hair cycle stage, a schematic drawing and representative micrographs are provided in order to illustrate these criteria. The basic criteria can be employed for most mouse strains and require only routine histochemical techniques, while the auxiliary criteria rely on the immunohistochemical analysis of three markers: interleukin-1 receptor type I, transforming growth factor beta receptor type II, and neuronal cell-adhesion molecule. These markers allow a precise analysis of anatomical hair follicle compartments during all hair cycle stages. In contrast to prior staging systems (Chase, Straile), we divide anagen III into three distinct substages, based on morphological differences, onset and progression of melanogenesis and the position of the dermal papilla in the subcutis. Computer-generated schematic representations of each hair cycle stage are provided with the aim of standardising further reports on follicular gene and protein expression patterns. The staging method provided here should become a useful tool when screening new mouse mutants or mice treated with pharmaceuticals even for discrete abnormalities of hair follicle cycling in a highly reproducible, easily applicable, and quantifiable manner.