Craniosynostosis, the premature fusion of calvarial
sutures, is a common
craniofacial abnormality. Causative mutations in more than 10 genes have been identified, involving
fibroblast growth factor,
transforming growth factor beta, and Eph/
ephrin signalling pathways. Mutations affect each human calvarial
suture (coronal, sagittal, metopic, and lambdoid) differently, suggesting different gene expression patterns exist in each human
suture. To better understand the molecular control of human
suture morphogenesis we used microarray analysis to identify genes differentially expressed during
suture fusion in children with
craniosynostosis. Expression differences were also analysed between each unfused
suture type, between
sutures from syndromic and non-syndromic
craniosynostosis patients, and between unfused
sutures from individuals with and without
craniosynostosis.
RESULTS: We identified genes with increased expression in unfused
sutures compared to fusing/fused
sutures that may be pivotal to the maintenance of
suture patency or in controlling early osteoblast differentiation (i.e. RBP4, GPC3, C1QTNF3, IL11RA, PTN, POSTN). In addition, we have identified genes with increased expression in fusing/fused
suture tissue that we suggest could have a role in premature
suture fusion (i.e. WIF1, ANXA3, CYFIP2).
Proteins of two of these genes,
glypican 3 and
retinol binding protein 4, were investigated by immunohistochemistry and localised to the
suture mesenchyme and osteogenic fronts of developing human calvaria, respectively, suggesting novel roles for these
proteins in the maintenance of
suture patency or in controlling early osteoblast differentiation. We show that there is limited difference in whole genome expression between
sutures isolated from patients with syndromic and non-syndromic
craniosynostosis and confirmed this by quantitative RT-PCR. Furthermore, distinct expression profiles for each unfused
suture type were noted, with the metopic
suture being most disparate. Finally, although calvarial bones are generally thought to grow without a cartilage precursor, we show histologically and by identification of cartilage-specific gene expression that cartilage may be involved in the morphogenesis of lambdoid and posterior sagittal
sutures.
CONCLUSION: