Fgf20 governs formation of primary and secondary dermal condensations in developing hair follicles - PubMed (original) (raw)

Fgf20 governs formation of primary and secondary dermal condensations in developing hair follicles

Sung-Ho Huh et al. Genes Dev. 2013.

Abstract

In hair follicle development, a placode-derived signal is believed to induce formation of the dermal condensation, an essential component of ectodermal organs. However, the identity of this signal is unknown. Furthermore, although induction and patterning of hair follicles are intimately linked, it is not known whether the mesenchymal condensation is necessary for inducing the initial epithelial pattern. Here, we show that fibroblast growth factor 20 (Fgf20) is expressed in hair placodes and is induced by and functions downstream from epithelial ectodysplasin (Eda)/Edar and Wnt/β-Catenin signaling to initiate formation of the underlying dermal condensation. Fgf20 governs formation of primary and secondary dermal condensations in developing hair follicles and subsequent formation of guard, awl, and auchene hairs. Although primary dermal condensations are absent in Fgf20 mutant mice, a regular array of hair placodes is formed, demonstrating that the epithelial patterning process is independent of known histological and molecular markers of underlying mesenchymal patterns during the initial stages of hair follicle development.

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Figures

Figure 1.

Figure 1.

Fgf20 is a target of Eda/Edar and Wnt/β-Catenin signal during hair placode formation. (A) Real-time quantitative PCR (qPCR) for Fgf20 from E14.5 Eda−/− skin explants with or without EDA treatment for 2 h (n = 12; P = 0.008) or 4 h (n = 6; P = 0.03). Data are shown as mean ± SD. (B) βGal staining indicating Fgf20βGal expression in K14-Eda;Fgf20βGal/+ and Eda−/−;Fgf20βGal/+embryos. (C) Assay showing that a 5.2-kb genomic DNA fragment upstream of the Fgf20 transcription initiation site driving luciferase was induced by transfection of a β-Catenin-Lef1 fusion protein (n = 9; P < 0.001). The vector control pGL3 showed no induction. Data are shown as mean ± SD. (D) βGal staining indicating Fgf20βGal expression in K14-Cre;β-CatΔEx3(βCatact);Fgf20βGal/+ and K14-Cre;β-CatF/F(βCatCKO);Fgf20βGal/+ embryos.

Figure 2.

Figure 2.

Loss of Fgf20 results in guard hair agenesis. (A) Image of 4-wk-old mice showing guard hair shafts sprouting from back skin in a Fgf20βGal/+ mouse (arrow, left) but not in a Fgf20βGal/βGal mouse (right). (B) Image of hairs from back skin of a Fgf20βGal/+ (left) or Fgf20βGal/βGal (right) mouse. (C) Quantification of hair types from 3-wk-old mice. Fgf20βGal/βGal mice show complete loss of guard hairs and decreased awl and auchene hairs. (D) Scanning electron micrograph showing primary hair follicle primordia as round protrusions in a Fgf20βGal/+ embryo, but the surface of a Fgf20βGal/βGal embryo appears flat. (E) Histology of E14.5, E15.5, E16.5, and E18.5 skin from Fgf20βGal/+ and Fgf20βGal/βGal embryos. Arrows indicate dermal condensations. (Bottom right panel) Note the bifurcated hair follicle. (au) Auchene; (g) guard; (aw) awl; (z) zigzag. Bar, 100 μm.

Figure 3.

Figure 3.

Fgf20 is required for dermal condensation development. (A) Phospho-Erk1/2 staining showing loss of Erk1/2 activity in dermis from Fgf20βGal/βGal skin (left) compared with control (right). (B–E) Coimmunostaining for Sox2 and P-Cadherin (Pcad) showing Sox2+ dermal condensations at E14 (B), E14.5 (C), E15.5 (D), and E16.5 (E) in Fgf20βGal/+ (left) but not in Fgf20βGal/βGal (right) embryo skin. (F–I) In situ hybridization of Bmp4 (F), p21 (G), Dkk1 (H), and Inhba (I) showing normal dermal expression in Fgf20βGal/+ (left) embryos and loss of expression in Fgf20βGal/βGal embryos (right). Bar, 100 μm.

Figure 4.

Figure 4.

Fgf20 modulates epithelial and mesenchymal Wnt/β-Catenin signaling during primary hair placode formation. (A–C) In situ hybridization for Wnt10b (A), Lef1 (B), and β-Catenin (C) showing stripe-like expression in Fgf20βGal/βGal embryos compared with Fgf20βGal/+ embryos. (D) Fgf20βGal staining showing increased interfollicular βGal staining in Fgf20βGal/βGal embryos compared with Fgf20βGal/+ embryos. (E) In situ hybridization of Axin2 showing increased expression in placodal cells but decreased expression in dermal cells in Fgf20βGal/βGal embryos compared with Fgf20βGal/+ embryos. (F) Immunostaining for β-Catenin showing loss of β-Catenin nuclear localization (arrows) in dermal cells in Fgf20βGal/βGal embryos compared with Fgf20βGal/+ embryos. (G) Immunostaining for Lef1 shows strong nuclear expression in the dermal condensation of Fgf20βGal/+ but not in Fgf20βGal/βGal embryos at E14.5. (H,I) In situ hybridization for Dkk4 (H) and Sostdc1 (I) showing severely reduced expression in Fgf20βGal/βGal embryos compared with Fgf20βGal/+ embryos. Bar, 100μm.

Figure 5.

Figure 5.

Fgf20 modulates Eda/Edar but not Shh signaling during primary hair placode formation. (A–B) In situ hybridization for Edar (A) and Iκ-Bα (B) showing decreased expression in Fgf20βGal/βGal embryos compared with Fgf20βGal/+ embryos. (C,D) In situ hybridization of Shh (C) and Patched1 (Ptch) (D) showing unaltered expression in Fgf20βGal/βGal embryos compared with Fgf20βGal/+ embryos. Bar, 100 μm.

Figure 6.

Figure 6.

Eda/Edar and Wnt/β-Catenin signaling-induced dermal condensation is _Fgf20_-dependent. (A) Coimmunostaining for Sox2 and P-Cadherin showing that Sox2+ dermal condensation induced by Eda overexpression (K14-Eda) has been abolished in Fgf20βGal/βGal embryos compared with Fgf20βGal/+ embryos at E14.5. (B) In situ hybridization for Iκ-Bα showing increased expression in K14-Eda and K14-Eda;Fgf20βGal/βGal embryos at E14.5. (C) Coimmunostaining for Sox2 and P-Cadherin at E13.5 showing that Sox2+ dermal condensations induced by K14-Cre;β-CatΔEx3 (βCatact) were absent in Fgf20βGal/βGal embryos compared with Fgf20βGal/+ embryos, yet premature induction of placodes was unaffected by loss of Fgf20 (cf. Supplemental Fig. S1A). Bar, 100 μm.

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