Project description:Sutures separate the flat bones of the skull and enable coordinated growth of the brain and overlying cranium. In order to uncover the cellular diversity within sutures, we conducted single-cell transcriptomic and histological analyses of the embryonic murine coronal suture. We identify Erg and Pthlh as early markers of osteogenic progenitors in sutures, and distinct pre-osteoblast signatures between the bone fronts and periosteum. diverse mesenchymal layers at the coronal suture, including multiple distinct meningeal layers below the suture, and ligamentous, ectocranial, and hypodermal layers above the sutureIn the ectocranial layers above the suture, we observe a ligament-like population spanning the frontal and parietal bones and expressing genes implicated in mechanosensation. Mesenchyme in and around the coronal suture is asymmetrically distributed between the frontal and parietal bones, and we identify different states of osteogenic cells extending from the bone fronts into the more mature bone, and a potential signature for sutural stem cellsIn the meningeal layers, we detect a potential chondrogenic periosteal dura population that may be involved in endochondral ossification that closes sutures. Expression of genes mutated in craniosynostosis is spread across diverse cell types, suggesting multiple points at which homeostasis can fail. This single-cell atlas provides a resource to understand the development of the coronal suture, the suture most commonly fused in craniosynostosis.
Project description:Craniofacial development depends on formation and maintenance of sutures between bones of the skull. In sutures, growth occurs at osteogenic fronts along the edge of each bone and suture mesenchyme separates adjacent bones. We performed single-cell RNA-seq analysis of the embryonic, murine coronal suture. Seven populations at E16.5 and nine at E18.5 comprised the suture mesenchyme, osteogenic cells, and associated populations. Expression of Hhip, an inhibitor of hedgehog (HH) signaling, marked a mesenchymal population distinct from other neurocranial sutures. At E18.5, Hhip-/- coronal osteogenic fronts were closely apposed and HH signaling was increased throughout the depleted suture mesenchyme compared to WT, demonstrating that Hhip is required for normal coronal suture development. Tracing of the neonatal Hhip-expressing population showed that descendant cells persisted in the coronal suture and contributed to calvarial bone growth. Our transcriptomic approach provides a rich resource for insight into normal and abnormal development.
Project description:Cranial sutures separate neighboring skull bones and contain skeletal stem cells that drive bone growth. A key question is how osteogenic activity is controlled to promote bone growth while preventing aberrant bone fusions during skull expansion. Here we integrate single-cell transcriptomics, in vivo expression validation, photoconversion-based lineage tracing, and a zebrafish craniosynostosis model to uncover key developmental transitions regulating bone formation during skull expansion. In addition to conservation of meninges and osteoblast lineage cells between zebrafish and mouse, single-cell transcriptomic analysis of the zebrafish skull reveals distinct subpopulations of suture mesenchyme that undergo transcriptomic changes during suture establishment. While lineage tracing with an osteoblast-specific nlsEOS reporter shows that bone formation largely occurs at suture edges, a subset of mesenchyme cells in the mid-suture region upregulate a suite of genes including BMP antagonists (e.g. grem1a) and pro-angiogenic factors. Further, lineage tracing with grem1a:nlsEOS reveals that this mid-suture subpopulation is largely non-osteogenic. In twist1b; tcf12 mutant zebrafish, a model for the coronal synostosis of Saethre-Chotzen Syndrome, reduction of grem1a+ mid-suture cells correlates with misregulated bone formation and reduced blood vessels at the coronal suture. In addition, combinatorial mutation of BMP antagonists enriched in the mid-suture subpopulation results in increased BMP signaling in the suture, misregulated bone formation, and abnormal suture morphology. These data support roles of a subset of mid-suture mesenchyme in locally promoting BMP antagonism that ensures proper suture morphology.
Project description:Craniosynostosis is a disease defined by premature fusion of one or more cranial sutures. The mechanistic pathology of isolated single-suture craniosynostosis is complex and while a number of genetic biomarkers and environmental predispositions have been identified, in many cases the causes remain controversial and inconclusive at best. After controlling for variables contributing to potential bias, FGF7, SFRP4, and VCAM1 emerged as potential genetic biomarkers for single-suture craniosynostosis due to their significantly large changes in gene expression compared to the control population. Furthermore, pathway analysis implicated focal adhesion and extracellular matrix (ECM)-receptor interaction as differentially regulated gene networks when comparing all cases of single-suture synostosis and controls. Lastly, overall gene expression was found to be highly conserved between coronal and metopic cases, as evidenced by the fact that WNT2 and IGFBP2 were the only differentially regulated genes identified in a direct comparison. These results not only confirm the roles of previously reported craniosynostosis-related targets but also introduce novel genetic biomarkers and pathways that may play critical roles in its pathogenesis. In this study, gene expression data from 199 patients with isolated sagittal (n= 100), unilateral coronal (n = 50), and metopic (n = 49) synostosis are compared against both a control population (n = 50), as well as each other.
Project description:Sutures separate the flat bones of the skull and enable coordinated growth of the brain and overlying cranium. The coronal suture is most commonly fused in monogenic craniosynostosis, yet the unique aspects of its development remain incompletely understood. To uncover the cellular diversity within the murine embryonic coronal suture, we generated single-cell transcriptomes and performed extensive expression validation. We find distinct pre-osteoblast signatures between the bone fronts and periosteum, a ligament-like population above the suture that persists into adulthood, and a chondrogenic-like population in the dura mater underlying the suture. Lineage tracing reveals an embryonic Six2+ osteoprogenitor population that contributes to the postnatal suture mesenchyme, with these progenitors being preferentially affected in a Twist1+/-; Tcf12+/- mouse model of Saethre-Chotzen Syndrome. This single-cell atlas provides a resource for understanding the development of the coronal suture and the mechanisms for its loss in craniosynostosis.
Project description:Craniosynostosis is a disease defined by premature fusion of one or more cranial sutures. The mechanistic pathology of isolated single-suture craniosynostosis is complex and while a number of genetic biomarkers and environmental predispositions have been identified, in many cases the causes remain controversial and inconclusive at best. After controlling for variables contributing to potential bias, FGF7, SFRP4, and VCAM1 emerged as potential genetic biomarkers for single-suture craniosynostosis due to their significantly large changes in gene expression compared to the control population. Furthermore, pathway analysis implicated focal adhesion and extracellular matrix (ECM)-receptor interaction as differentially regulated gene networks when comparing all cases of single-suture synostosis and controls. Lastly, overall gene expression was found to be highly conserved between coronal and metopic cases, as evidenced by the fact that WNT2 and IGFBP2 were the only differentially regulated genes identified in a direct comparison. These results not only confirm the roles of previously reported craniosynostosis-related targets but also introduce novel genetic biomarkers and pathways that may play critical roles in its pathogenesis.
Project description:Purpose: The cranial suture is a fibrous joint, and similar to the growth plates of the skeletal long bone, they serve as the major centers of calvarial vault morphogenesis. Our group’s identification of a skeletal stem cell isolated from the mouse tibial growth plate prompted us to investigate whether these skeletal stem cells are also resident in the mouse cranial sutures and if they govern postnatal suture patency or fusion. Results: We preformed a spatio-temporal profiling of the mouse cranial sutures by flow cytometry, demonstrating a significant decrease in the temporal representation of skeletal stem cells in fusing versus patent sutures. Moreover, canonical Wnt signaling has a significant impact on skeletal stem cells proliferation and thus representation within the suture, dictating fate: fusion or patency. Breeding an Axin2+/-LacZ mouse, with enhanced activation of canonical Wnt signaling to a Twist1+/− mouse, harboring a coronal craniosynostosis enriched the skeletal stem cell pool in coronal sutures, thereby preventing Twist1+/− craniosynostosis. Conclusions: Our findings suggest an imbalance and/or decrease in resident skeletal stem cells within the cranial sutures gives rise to craniosynostosis, however, restoring this representation by enriching skeletal stem cells within the suture can maintain patency.
Project description:Purpose: The cranial suture is a fibrous joint, and similar to the growth plates of the skeletal long bone, they serve as the major centers of calvarial vault morphogenesis. Our group’s identification of a skeletal stem cell isolated from the mouse tibial growth plate prompted us to investigate whether these skeletal stem cells are also resident in the mouse cranial sutures and if they govern postnatal suture patency or fusion. Results: We preformed a spatio-temporal profiling of the mouse cranial sutures by flow cytometry, demonstrating a significant decrease in the temporal representation of skeletal stem cells in fusing versus patent sutures. Moreover, canonical Wnt signaling has a significant impact on skeletal stem cells proliferation and thus representation within the suture, dictating fate: fusion or patency. Breeding an Axin2+/-LacZ mouse, with enhanced activation of canonical Wnt signaling to a Twist1+/− mouse, harboring a coronal craniosynostosis enriched the skeletal stem cell pool in coronal sutures, thereby preventing Twist1+/− craniosynostosis. Conclusions: Our findings suggest an imbalance and/or decrease in resident skeletal stem cells within the cranial sutures gives rise to craniosynostosis, however, restoring this representation by enriching skeletal stem cells within the suture can maintain patency.
Project description:Axin2-expressing calvarial suture stem cells can contribute to calvarial development, homeostatic maintenance, repair, and regeneration. We used microarray to examine the gene expression profiles of Axin2-expressing suture stem cells and Axin2-negative cells in suture mesenchyme.