Tissue-specific responses to aberrant FGF signaling in complex head phenotypes.

BACKGROUND: The role of fibroblast growth factor and receptor (FGF/FGFR) signaling in bone development is well studied, partly because mutations in FGFRs cause human diseases of achondroplasia and FGFR-related craniosynostosis syndromes including Crouzon syndrome. The FGFR2c C342Y mutation is a frequent cause of Crouzon syndrome, characterized by premature cranial vault suture closure, midfacial deficiency, and neurocranial dysmorphology. Here, using newborn Fgfr2c(C342Y/+) Crouzon syndrome mice, we tested whether the phenotypic effects of this mutation go beyond the skeletal tissues of the skull, altering the development of other non-skeletal head tissues including the brain, the eyes, the nasopharynx, and the inner ears. RESULTS: Quantitative analysis of 3D multimodal imaging (high-resolution micro-computed tomography and magnetic resonance microscopy) revealed local differences in skull morphology and coronal suture patency between Fgfr2c(C342Y/+) mice and unaffected littermates, as well as changes in brain shape but not brain size, significant reductions in nasopharyngeal and eye volumes, and no difference in inner ear volume in Fgfr2c(C342Y/+) mice. CONCLUSIONS: These findings provide an expanded catalogue of clinical phenotypes in Crouzon syndrome caused by aberrant FGF/FGFR signaling and evidence of the broad role for FGF/FGFR signaling in development and evolution of the vertebrate head.

The skeletal site-specific role of connective tissue growth factor in prenatal osteogenesis.

BACKGROUND: Connective tissue growth factor (CTGF/CCN2) is a matricellular protein that is highly expressed during bone development. Mice with global CTGF ablation (knockout, KO) have multiple skeletal dysmorphisms and perinatal lethality. A quantitative analysis of the bone phenotype has not been conducted. RESULTS: We demonstrated skeletal site-specific changes in growth plate organization, bone microarchitecture, and shape and gene expression levels in CTGF KO compared with wild-type mice. Growth plate malformations included reduced proliferation zone and increased hypertrophic zone lengths. Appendicular skeletal sites demonstrated decreased metaphyseal trabecular bone, while having increased mid-diaphyseal bone and osteogenic expression markers. Axial skeletal analysis showed decreased bone in caudal vertebral bodies, mandibles, and parietal bones in CTGF KO mice, with decreased expression of osteogenic markers. Analysis of skull phenotypes demonstrated global and regional differences in CTGF KO skull shape resulting from allometric (size-based) and nonallometric shape changes. Localized differences in skull morphology included increased skull width and decreased skull length. Dysregulation of the transforming growth factor-ß-CTGF axis coupled with unique morphologic traits provides a potential mechanistic explanation for the skull phenotype. CONCLUSIONS: We present novel data on a skeletal phenotype in CTGF KO mice, in which ablation of CTGF causes site-specific aberrations in bone formation.