Studies in cranial suture biology: regional dura mater determines in vitro cranial suture fusion

Craniosynostosis results in alterations in craniofacial growth that create cosmetic abnormalities and functional deficits, yet the biology underlying cranial suture fusion remains unknown. The purpose of the present study was to show that regional dura mater can induce suture fusion while in an organ culture system in cranial sutures programmed to remain patient. To accomplish this, we studied mouse cranial sutures, since in this model the posterior frontal suture (analogous to the human metopic suture) fuses in both in vivo and in vitro environments while all other sutures remain patent. We demonstrated that when mouse sagittal sutures (programmed to remain patent) were rotated or translocated to overlie the posterior frontal dura then grown in organ culture systems, suture fusion occurred. Twenty-four-day-old CD-1 mice (time when the posterior frontal suture was patent) were divided into three groups of 50 (n = 165: three groups of 50 cultured and three groups of 5 uncultured controls). Group A (unrotated control group) was characterized by a strip of posterior frontal and sagittal suture with underlying dural tissue grown in organ culture systems for up to 30 days and resulted in persistent patency of the sagittal suture and fusion of the posterior frontal suture in an anterior-to-posterior direction. Group B (rotated experimental group) was characterized by 180-degree suture rotation while in vitro and resulted in patency of the posterior frontal suture over the sagittal dura and fusion of the sagittal suture over the posterior frontal dura in a posterior-to-anterior suture direction. Group C (translocated experimental group) was characterized by translocation or shifting of sutures while in vitro and resulted in patency of the posterior frontal suture over the sagittal dura and fusion of the sagittal suture over the posterior frontal dura in an anterior-to-posterior suture direction. These data from the in vitro rotation and translocation experiments indicate that the "regional" posterior frontal dura determined in vitro cranial suture fusion. Molecular mechanisms behind this process are thought to involve inductive tissue interactions of the dural cells with the suture cells by means of growth factor-mediated signal pathways.