Grant: Discovery Grants Program - Individual

The vertebrate skull houses the jaws, the brain and sensory organs, and as such, plays essential functional and protective roles. Skull development and shape are likewise influenced by these adjacent structures through complex tissue interactions, such as those between the skull and the brain, meninges, sutures and cranial cartilages. A main focus of my current NSERC DG-funded research has been to explore the interplay between cranial bone and cartilage throughout development. Prior to calvarial bone formation, the brain is surrounded by cartilages, some of which persist (nasal cartilages), contribute to the cranial base through endochondral ossification, and some that are transient, and dissolve as overlying intramembranous bones ossify. Although originally described over 90 years ago, the development and relative positioning of the transient cranial cartilages have only recently been characterized in detail. Studies using mouse models have demonstrated that these transient cartilages form at embryonic day (E) 12.5, coalesce by E15.5 and begin to disappear at E16.5. These cartilages are paired with overlying intramembranous bones of the calvaria, and the timing of their appearance and disappearance is coordinated with ossification of the intramembranous bones. Moreover, in mouse models wherein the cranial cartilages are absent, the overlying intramembranous bones are small and dysplastic. This close association between the cranial cartilages and the overlying intramembranous bones of the calvaria suggests that their development is linked, yet the mechanisms of their interaction over development are unknown. Therefore, the goal of this proposed work is to uncover the specific mechanisms of interaction through which these transient cartilages affect intramembranous bone formation. To achieve this goal, we will explore the hypothesis that transient cranial cartilages influence intramembranous bone formation through molecular signaling and by modulating the mechanical environment using in vivo, ex vivo and in vitro approaches. Objective 1. Determine the role of transient cranial cartilage in intramembranous bone ossification over developmental time. We will use contrast-enhanced micro-CT to simultaneously image bone and cartilage in developing mouse skulls. Objective 2. Investigate signaling interactions between transient cranial cartilages and overlying intramembranous bones. We will use spatial transcriptomics and explant culture models. Objective 3. Determine the effect of transient cranial cartilage stiffness on mesenchymal stem cell differentiation. We will use cell culture and biomechanical testing. The proposed studies will provide the first evidence of the mechanisms of interaction between the transient cranial cartilages and their overlying intramembranous bones. Moreover, our findings may indicate a re-evaluation of the long-standing description of intramembranous ossification as independent of cartilage development.