A molecular analysis of the isolated rat posterior frontal and sagittal sutures: Differences in gene expression

Although it is one of the most commonly occurring craniofacial congenital d isabilities, craniosynostosis (the premature fusion of cranial sutures) is nearly impossible to prevent because the molecular mechanisms that regulate the process of cranial suture fusion remain largely unknown. Recent studie s have implicated the dura mater in determining the fate of the overlying c ranial suture; however, the molecular biology within the suture itself has not been sufficiently investigated. In the murine model of cranial suture f usion, the posterior frontal suture is programmed to begin fusing by postna tal day 12 in rats (day 25 in mice), reliably completing bony union by post natal day 22 (day 45 in mice). In contrast, the sagittal suture remains pat ent throughout the life of the animal. Using this model, this study sought to examine for the first time what differences in gene expression - if any - exist between the two sutures with opposite fates. For each series of experiments, 35 to 40 posterior frontal and sagittal sut ure complexes were isolated from 6-day-old Sprague-Dawley rat pups. Suture- derived cell cultures were established, and ribonucleic acid was derived fo rm snap-frozen, isolated suture tissue. Results demonstrated that molecular differences between the posterior frontal and sagittal suture complexes we re readily identified in vivo, although these distinctions were lost once t he cells comprising the suture complex were cultured in vitro. Hypothetical ly, this change in gene expression resulted from the loss of the influence of the underlying dura mater. Significant differences in the expression of genes encoding extracellular matrix proteins existed in vivo between the po sterior frontal and sagittal sutures. However, the production of the critic al, regulatory cytokine transforming growth factor beta-1 was equal between the two suture complexes, lending further support to the hypothesis that d ura mater regulates the fate of the overlying cranial suture.