STUDIES IN CRANIAL SUTURE BIOLOGY - IN-VITRO CRANIAL SUTURE FUSION

The biology underlying craniosynostosis remains unknown. Previous stud ies have shown that the underlying dura mater, not the suture itself, signals a suture to fuse. The purpose of this study was to develop an in vitro model for cranial-suture fusion that would still allow for su ture-dura interaction, but without the influence of tensional forces t ransmitted from the cranial base. This was accomplished by demonstrati ng that the posterior frontal mouse cranial suture, known to be the on ly cranial suture that fuses in vivo, fuses when plated with its dura in an organ-culture system. In such an organ-culture system, the sutur es are free from both the influence of dural forces transmitted from t he cranial base and from hormonal influences only available in a perfu sed system. For the cranial-suture fusion in vitro model study, the sa gittal sutures (controls that remain patent in vivo) and posterior fro ntal sutures (that fuse in vivo) with the underlying dura were excised from 24-day-old euthanized mice, cut into 5 x 4 x 2-mm specimens, and cultured in a chemically defined, serum-free media. One hundred sutur es were harvested at the day of sacrifice, then every 2 days thereafte r until 30 days in culture, stained with H & E, and analyzed. A subseq uent cranial-suture without dura in vitro study was performed in a sim ilar fashion to the first study, but only the calvariae with the poste rior frontal or sagittal sutures (without the underlying dura) were cu ltured. Results from the cranial-suture fusion in vitro model study sh owed that all sagittal sutures placed in organ culture with the underl ying dura remained patent. More importantly, the posterior frontal sut ures with the underlying dura, which were plated-down as patent at 24 days of age, demonstrated fusion after various growth periods in organ culture. in vitro posterior frontal mouse-suture fusion occurred in a n anterior-to-posterior direction but in a delayed fashion, 4 to 7 day s later than in vivo posterior frontal mouse-suture fusion. In contras t, the subsequent cranial-suture without dura in vitro study showed pa tency of all sutures, including the posterior frontal suture. These da ta from in vitro experiments indicate that : (1) mouse calvariae, sutu res, and the underlying dura survive and grow in organ-culture systems for 30 days; (2) the local dura, free from external influences transm itted from the cranial base and hormones from distant sites, influence s the cells of its overlying suture to cause fusion; and (3) without d ura influence, all in vitro cranial sutures remained patent. By first identifying the factors involved in dural-suture signaling and then re gulating these factors and their receptors, the biologic basis of sutu re fusion and craniosynostosis may be unraveled and used in the future to manipulate pathologic (premature) suture fusion.