FGF22 in Skin Development and Repair Figure 3. Normal wound repair in fgf22 knockout mice. A) H&E stained tissue sections of 3 mm punch biopsy wounds 5 days after wounding. B1–B2) Tissue sections immunostained for 5-bromo-2-deoxyuridine. High power fields in B2) focus on BrdU-positive cells (brown) at the wound site. C and D) Sirius red staining of sections from wild type and fgf22 knockout male mice skin 14 days post-wounding. C) represents the same section in bright field as D) in dark field. The spectrum of colours from green, yellow, orange and red progressively exhibits the packing of collagen molecules. (D dermis, HE hyperproliferative epidermis, HF hair follicle, G granulation tissue, BC blood clot. Wound margins are indicated by arrows). Scale bar (200 mm) in A, B1, C, D; (50 mm) in B2. E). The percentage positive BrdU score was calculated from immunostained sections from B1 by counting the total number of positive and negative cells within the wound margins and then deriving the percentage of positive cells. Plots represent mean of three independent wounds per genotype per time point where two slides per wound were counted. Error bars represent SEM. F) and G) Morphometric analysis of wound repair. Morphometric measurements of wounds were performed on three independent wounds for each genotype and each time point. F) Wound gap was calculated as the distance between two margins of the inward growing epithelium and was measured three times for each wound section. G) The area of migrating epithelial tongue was also measured. Error bars represent SEM. doi:10.1371/journal.pone.0039436.g003 little is known about the role and importance of FGF22 in these processes. Previous studies have shown that FGF22 is expressed in the brain, where it is essential for the development of excitatory synapses [28]. Furthermore, FGF22 deficient mice, generated commercially (Deltagen, San Mateo, CA), are resistant to pentylenetetrazol-induced epileptic seizures [29], though lack of FGF22 does not affect behaviour in unchallenged mice. FGF22 is expressed in the inner root sheath of the hair follicle [11] and has been shown to bind to FGFR2b [4]. Since there was a clear defect in hair development in fgfr2b skin [19], we analysed the hair of fgf22 knockout mice. All three major hair types were present in identical proportions to those seen in wild type littermates and no effects on sebaceous gland morphology were observed, suggesting either that redundancy prevents occurrence of an overt phenotype in the fgf22 knockout mouse, or that its role is non-essential in unchallenged skin. Recent studies have established that signaling downstream of FGFR2b and FGFR1b is essential for skin homeostasis and epidermal barrier function, PLoS ONE | www.plosone.org 5 June 2012 | Volume 7 | Issue 6 | e39436