Craniosynostosis is the premature fusion of calvarial sutures. It results from abnormal differentiation or proliferation of cells within the osteogenic fronts of growing calvarial bones. To date, research has focused on animal models and in vitro organ and tissue culture to determine the molecular mechanisms controlling calvarial suture morphogenesis. Here, we test a new, in vivo-in vitro approach based on the hypothesis that calvarial suture cells passaged in minimal medium exhibit a stable gene expression profile similar to undifferentiated osteoblastic cells that can provide a benchmark for comparison with in vivo expression of differentiated tissue. We show that tissue-specific expression is lost after the first passage and, using cDNA microarrays, compare expression between fused suture tissue from craniosynostosis patients and in vitro de-differentiated explant cells. A large number of differentially expressed genes were identified, including novel genes WIF1, LEF1, SATB2, RARRES1, DEFA1, DMP1, PTPRZ1, and PTPRC, as well as those commonly associated with human suture morphogenesis, e.g., FGF2, MSX2, and BMP2. Two differentially expressed genes, WIF1 and FGF2, were further examined in an in vivo-in vivo comparison between unfused and prematurely fused tissue. The same pattern of differential expression was observed in each case, further validating the ability of our in vivo-in vitro approach to identify genes involved in in vivo human calvarial tissue differentiation. ; Anna K. Coussens, Ian P. Hughes, Christopher R. Wilkinson, C. Phillip Morris, Peter J. Anderson, Barry C. Powell and Angela van Daal ; The definitive version may be found at www.wiley.com