title: Analysis of theFgfr2C342Ymouse model shows condensation defects due to misregulation ofSox9expression in prechondrocytic mesenchyme.
abstract: Syndromic craniosynostosis caused by mutations inFGFR2is characterised by developmental pathology in both endochondral and membranous skeletogenesis. Detailed phenotypic characterisation of features in the membranous calvarium, the endochondral cranial base and other structures in the axial and appendicular skeleton has not been performed at embryonic stages. We investigated bone development in the Crouzon mouse model (Fgfr2C342Y) at pre- and post-ossification stages to improve understanding of the underlying pathogenesis. Phenotypic analysis was performed by whole-mount skeletal staining (Alcian Blue/Alizarin Red) and histological staining of sections of CD1 wild-type (WT),Fgfr2C342Y/+heterozygous (HET) andFgfr2C342Y/C342Yhomozygous (HOM) mouse embryos from embryonic day (E)12.5-E17.5 stages. Gene expression (Sox9,Shh,Fgf10andRunx2) was studied byin situhybridisation and protein expression (COL2A1) by immunohistochemistry. Our analysis has identified severely decreased osteogenesis in parts of the craniofacial skeleton together with increased chondrogenesis in parts of the endochondral and cartilaginous skeleton in HOM embryos. TheSox9expression domain in tracheal and basi-cranial chondrocytic precursors at E13.5 in HOM embryos is increased and expanded, correlating with the phenotypic observations which suggest FGFR2 signalling regulatesSox9expression. Combined with abnormal staining of type II collagen in pre-chondrocytic mesenchyme, this is indicative of a mesenchymal condensation defect. An expanded spectrum of phenotypic features observed in theFgfr2C342Y/C342Ymouse embryo paves the way towards better understanding the clinical attributes of human Crouzon-Pfeiffer syndrome.FGFR2mutation results in impaired skeletogenesis; however, our findings suggest that many phenotypic aberrations stem from a primary failure of pre-chondrogenic/osteogenic mesenchymal condensation and link FGFR2 to SOX9, a principal regulator of skeletogenesis.
authors.affiliation: UCL Great Ormond Street, Institute of Child Health, University College London, London, WC1N 1EH, UK.
authors.forename: Emma
authors.initials: E
authors.lastname: Peskett
authors.affiliation: UCL Great Ormond Street, Institute of Child Health, University College London, London, WC1N 1EH, UK.
authors.forename: Samin
authors.initials: S
authors.lastname: Kumar
authors.affiliation: UCL Great Ormond Street, Institute of Child Health, University College London, London, WC1N 1EH, UK.
authors.forename: William
authors.initials: W
authors.lastname: Baird
authors.affiliation: UCL Great Ormond Street, Institute of Child Health, University College London, London, WC1N 1EH, UK.
authors.forename: Janhvi
authors.initials: J
authors.lastname: Jaiswal
authors.affiliation: UCL Great Ormond Street, Institute of Child Health, University College London, London, WC1N 1EH, UK.
authors.forename: Ming
authors.initials: M
authors.lastname: Li
authors.affiliation: UCL Great Ormond Street, Institute of Child Health, University College London, London, WC1N 1EH, UK.
authors.forename: Priyanca
authors.initials: P
authors.lastname: Patel
authors.affiliation: Craniofacial Unit, Great Ormond Street Hospital, London, WC1N 3JH, UK.
authors.forename: Jonathan A
authors.initials: JA
authors.lastname: Britto
authors.affiliation: UCL Great Ormond Street, Institute of Child Health, University College London, London, WC1N 1EH, UK e.pauws@ucl.ac.uk.
authors.forename: Erwin
authors.identifier: http://orcid.org/0000-0003-1751-0317
authors.initials: E
authors.lastname: Pauws
keywords: Craniosynostosis; Crouzon; FGFR2; Mesenchyme; RUNX2; SOX9