The Intertwined Evolution and Development of Sutures and Cranial Morphology

Abstract

Phenotypic variation across mammals is extensive and reflects their ecological diversification into a remarkable range of habitats on every continent and in every ocean. The skull performs many functions to enable each species to thrive within its unique ecological niche, from prey acquisition, feeding, sensory capture (supporting vision and hearing) to brain protection. Diversity of skull function is reflected by its complex and highly variable morphology. Cranial morphology can be quantified using geometric morphometric techniques to offer invaluable insights into evolutionary patterns, ecomorphology, development, taxonomy, and phylogenetics. Therefore, the skull is one of the best suited skeletal elements for developmental and evolutionary analyses. In contrast, less attention is dedicated to the fibrous sutural joints separating the cranial bones. Throughout postnatal craniofacial development, sutures function as sites of bone growth, accommodating expansion of a growing brain. As growth frontiers, cranial sutures are actively responsible for the size and shape of the cranial bones, with overall skull shape being altered by changes to both the level and time period of activity of a given cranial suture. In keeping with this, pathological premature closure of sutures postnatally causes profound misshaping of the skull (craniosynostosis). Beyond this crucial role, sutures also function postnatally to provide locomotive shock absorption, allow joint mobility during feeding, and, in later postnatal stages, suture fusion acts to protect the developed brain. All these sutural functions have a clear impact on overall cranial function, development and morphology, and highlight the importance that patterns of suture development have in shaping the diversity of cranial morphology across taxa. Here we focus on the mammalian cranial system and review the intrinsic relationship between suture development and morphology and cranial shape from an evolutionary developmental biology perspective, with a view to understanding the influence of sutures on evolutionary diversity. Future work integrating suture development into a comparative evolutionary framework will be instrumental to understanding how developmental mechanisms shaping sutures ultimately influence evolutionary diversity.

Ciliary Signalling and Mechanotransduction in the Pathophysiology of Craniosynostosis

“…The two MSC types have different topographical distributions in the newly formed skull: neural crest-derived cells (NCCs) will form the frontal bone and the entire facial skeleton, while the paraxial mesoderm will form the rest of the neurocranium, which has indeed an entirely mesodermal origin [ 63 ]. This way, the cranium develops, in all vertebrate species, by integrating genetic inputs and mechanical forces from growing soft tissues to determine skull morphology [ 64 ]. In these processes, the primary cilium serves as a signalling hub and a mechanotransduction relay among the forebrain neuroectoderm, the surface ectoderm, the endoderm and cranial neural crest cells.…”

The clinical manifestations, molecular mechanisms and treatment of craniosynostosis

“…These mesenchymal cells originate from either head mesoderm or cranial neural crest cells. Furthermore, cranial sutures are often positioned at the boundary of cranial neural crest- and mesoderm-derived bony elements ( Ishii, et al, 2015 ; White et al, 2021 ).…”

Cranial Suture Mesenchymal Stem Cells: Insights and Advances

“…It has been well established that the derivation of the skull vault comes from dual tissue lineages, namely, paraxial mesoderm and cranial neural crest [13][14][15]. As for the cranial sutures, not only do the sutures separate bones of different embryological origin, but they are themselves derived from different origins [15].…”

“…It has been well established that the derivation of the skull vault comes from dual tissue lineages, namely, paraxial mesoderm and cranial neural crest [13][14][15]. As for the cranial sutures, not only do the sutures separate bones of different embryological origin, but they are themselves derived from different origins [15]. For instance, sutures derived from cranial neural crest include metopic sutures and sagittal sutures, while coronal sutures derived from paraxial mesoderm and the developmental origin of the lambdoid sutures remains unknown [13,15].…”

“…As for the cranial sutures, not only do the sutures separate bones of different embryological origin, but they are themselves derived from different origins [15]. For instance, sutures derived from cranial neural crest include metopic sutures and sagittal sutures, while coronal sutures derived from paraxial mesoderm and the developmental origin of the lambdoid sutures remains unknown [13,15]. Differing in embryonic origin may lead to distinct capabilities of SuSCs in different sutures.…”