Fgf8 is Necessary for Normal Frontonasal Development

Abstract

Problem Craniofacial development is a complex process. We explore the role of ectodermal Fgf8 during craniofacial development in mice. Fgf8 is a multi-functional growth factor known to induce cell migration and differentiation. We hypothesize that Fgf8 is necessary for frontonasal development. To determine its role, we selectively removed Fgf8 signaling in cells expressing the AP2 gene. Methods We generated AP2 Cre Fgf8 f/f R26R mice at e13–18. The embryos are harvested and fixed. They are dehydrated or saturated in 30% sucrose, then embedded in paraffin or OCT compound, respectively, for sectioning. The paraffin sections are used for morphologic examination following H&E and PAS staining. The cryosections are used for X-gal staining and immunofluorescence. Skeletal preparations are used to assess the craniofacial skeleton. Results AP2 Cre mice are examined identifying AP2 expression in the developing epithelium. Gross examination of the AP2 Cre Fgf8 f/f mice reveals severe mid-face shortening and micrognathia. These mice are nonviable due to their severe facial abnormalities. Close inspection reveals prominent eyes that appear normally formed but lack eyelids. The skeletal preparation of the AP2 Cre Fgf8 f/f mouse demonstrates almost absent mandibular development and hypoplastic maxilla. This correlates with the hypoplastic, ill-organized sinus cavities with lack of nasal septum development seen on histologic sections. Examination of the epithelium and oral mucosa of these mutant mice demonstrates a verrucous morphology with poor differentiation. Conclusion Fgf8 expression in the ectoderm appears to be necessary for frontonasal development in mice. Without epithelial Fgf8 expression, the craniofacial and epidermal development is severely affected. Future studies will further characterize the epithelial and mesenchymal phenotype of the AP2 Cre Fgf8 f/f mutant mice. Significance The Fibroblast Growth Factor (Fgf) family is involved in multiple steps of craniofacial formation. Further studies elucidating the specific roles of its members, including Fgf8, will help better understand and manage craniofacial malformations.