Expression of Fgf signalling pathway related genes during palatal rugae development in the mouse Thantrira Porntaveetus, Shelly Oommen, Paul T. Sharpe, Atsushi Ohazama * Department of Craniofacial Development, Dental Institute, King’s College London, Guy’s Hospital, London Bridge, London SE1 9RT, UK article info Article history: Received 21 January 2010 Received in revised form 16 March 2010 Accepted 21 March 2010 Available online 27 March 2010 Keywords: Palatal rugae development Placode Interplacode Epithelium Mesenchyme Fgf Fgfr Sprouty Etv abstract Fgf signalling plays critical roles in the development of many ectodermal organs. Palatal rugae are ecto- dermal corrugated structures of the hard palate and in common with other ectodermal appendages, their development is initiated as epithelial thickenings that form placodes as the underlying mesenchy- mal cells condense. The placode regions then bulge towards to oral cavity to form an overall corrugated appearance. We carried out comparative in situ hybridization analysis of 18 Fgf ligands (Fgf1–Fgf10, Fgf15–Fgf18, Fgf20–Fgf23), four Fgf receptors (Fgfr1–Fgfr4) and four other Fgf signalling related mole- cules (Spry1, Spry2, Spry4 and Etv5) during murine palatal rugae development. Fgfr1 and Etv5 showed restricted expression in the interplacode epithelium whereas Fgf18 expression was localized to mesen- chyme underneath the interplacode epithelium. The expression of Fgf9 was restricted to epithelial ruga placodes whereas Spry4 expression was observed in mesenchyme underneath the placodes. The local- ized expression of Fgf2, Fgf8, Fgf16, Fgfr4 and Spry1 were found in bulge mesenchyme. Fgf3, Fgf6, Fgfr2 and Spry2 showed expression in the entire epithelium whereas Fgf10 was expressed throughout the mesenchyme. Fgf signalling thus shows dynamic temporo-spatial expression in murine palatal rugae development. Ó 2010 Elsevier B.V. All rights reserved. All ectodermal appendages (e.g. hair, teeth, nails, feathers, scales and glands) are derivatives of the embryonic ectoderm and develop through epithelial–mesenchymal interactions. De- spite the diversity and the highly specialized functions of these organs, they share common features during early stages of devel- opment where epithelium thickens to form placodes and the underlying mesenchymal cells condense (Thesleff et al., 1995; Pispa and Thesleff, 2003; Mikkola, 2007). In addition to structural features, these organs also utilize similar signalling pathways including Wnt, Shh, Bmp and Fgf during early stages of their development (Thesleff et al., 1995; Pispa and Thesleff, 2003; Mikkola, 2007). Palatal rugae are corrugated structures of the hard palate. They are thought to assist the holding and crushing of food between the tongue and the palate and aid the tongue’s correct placement for the production of certain speech sounds. Numerous nerve fi- bers are found to assemble in the rugae, which are considered to respond to touch and pressure on the palate during chewing, swallowing and speech (Mitsui et al., 2000; Ichikawa et al., 2001; Kido et al., 2003; Nunzi et al., 2004). Chemosensory taste bud-like structures are also localized on the hard palate, suggest- ing that rugae may serve for exteroception (Tachibana et al., 1990, 1991). Eight or nine palatal rugae are observed in mice. Three transverse ridges called antemolar rugae are formed just behind the incisor teeth. Five or six intermolar rugae are dis- played between the molar tooth fields. These rugae are shorter, more oblique and do not cross the midline (Fig. 1A; Sakamoto et al., 1989). The first morphological sign of rugae development is local thickening of the palatal epithelium to form placodes whilst the underlying mesenchymal cells condense (Fig. 1B). The placodes can be detected as slight protrusions on the surface of the develop- ing palate as the thickened epithelium protrudes over the surface. The placode regions then bulge towards to oral cavity to form an overall corrugated appearance (Fig. 1B; Peterkova et al., 1987). Placode formation and subsequent swelling are thus crucial events in palatal rugae development. Although palatal rugae development is under strict genetic control, since their number and the patterns are species specific, the molecular mechanisms regulating their development are largely unknown (Charles et al., 2007; Pantalacci et al., 2008, 2009; Welsh and O’Brien, 2009). Fibroblast growth factor (Fgf) signalling pathway is highly con- served in evolution and plays critical roles in many different bio- logical processes (Mason, 2007; Powers et al., 2000). Twenty-two 1567-133X/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.gep.2010.03.004 * Corresponding author. Address: Department of Craniofacial Development, Floor 27, Dental Institute, Guy’s Hospital, London Bridge, London SE1 9RT, UK. Tel.: +44 20 7188 8029; fax: +44 20 7188 1674. E-mail address: atsushi.2.ohazama@kcl.ac.uk (A. Ohazama). Gene Expression Patterns 10 (2010) 193–198 Contents lists available at ScienceDirect Gene Expression Patterns journal homepage: www.elsevier.com/locate/gep