Cranial sutures as intramembranous bone growth sites

Abstract

Intramembranous bone growth is achieved through bone formation within a periosteum or by bone formation at sutures. Sutures are formed during embryonic development at the sites of approximation of the membranous bones of the craniofacial skeleton. They serve as the major sites of bone expansion during postnatal craniofacial growth. For sutures to function as intramembranous bone growth sites, they need to remain in an unossified state, yet allow new bone to be formed at the edges of the overlapping bone fronts. This process relies on the production of sufficient new bone cells to be recruited into the bone fronts, while ensuring that the cells within the suture remain undifferentiated. Unlike endochondral growth plates, which expand through chondrocyte hypertrophy, sutures do not have intrinsic growth potential. Rather, they produce new bone at the sutural edges of the bone fronts in response to external stimuli, such as signals arising from the expanding neurocranium. This process allows growth of the cranial vault to be coordinated with growth of the neurocranium. Too little or delayed bone growth will result in wide-open fontanels and suture agenesis, whereas too much or accelerated bone growth will result in osseous obliteration of the sutures or craniosynostosis. Craniosynostosis in humans, suture fusion in animals, and induced suture obliteration in vitro has been associated with mutations or alterations in expression of several transcription factors, growth factors, and their receptors. Much of the data concerning signaling within sutures has been garnered from research on cranial sutures; hence, only the cranial sutures will be discussed in detail in this review. This review synthesizes classic descriptions of suture growth and pathology with modern molecular analysis of genetics and cell function in normal and abnormal suture morphogenesis and growth in a unifying hypothesis. At the same time, the reader is reminded of the importance of the suture as an intramembranous bone growth site.

Nasal Septal and Premaxillary Developmental Integration: Implications for Facial Reduction in Homo

“…Unlike neurocranial sutures, which are regulated via tissue interaction with the dura matter (Opperman et al, 1995;Opperman, 2002), the nasal septal cartilage itself may play an important role in the morphogenesis and regulation of facial sutures (Adab et al, 2002(Adab et al, , 2003. Thus, in addition to passively placing the premaxillary suture under biomechanical strains, thereby promoting osteoblastic and fibroblastic activity (e.g., Rafferty and Herring, 1999;Kopher and Mao, 2002;Mao et al, 2003;Mao, 2006;Katsaros et al, 2006), the nasal septum may also play a more active role in premaxillary suture development.…”

Histology‐Based Morphology of the Neurocentral Synchondrosis in Alligator Mississippiensis (Archosauria, Crocodylia)

“…Combinations of intrinsic (e.g., vascular, genetic, hormonal), extrinsic (e.g., mechanical), and epigenetic factors have been suggested in some craniofacial sutures in various mammals (e.g., Herring, 1993). Some specific genes have been identified for the mechanism of both patent and fused sutures (Opperman, 2000;Hall, 2005). These findings are extremely important for the understanding of the mechanism of sutural growth because the patterns of fusion in those craniofacial sutures can be homologous across different groups of mammals and possibly other vertebrates.…”

Expression of NG2 proteoglycan during endochondral and intramembranous ossification

“…Cranial sutures are the major sites of bone growth along cranial bone fronts during craniofacial development (Opperman, 2000). The tips of the two parietal bone fronts overlap one another, and a highly cellular suture matrix containing large numbers of osteoprogenitor cells and preosteoblasts (Liu et al, 1999) separates the bones of the 3-day-old sagittal suture (Fig.…”