Sutural fibroblasts exhibit the function of vascular endothelial cells upon mechanical strain.

Midfacial hypoplasia is a type of facial dysplasia. The technique of trans-sutural distraction osteogenesis promotes midface growth so as to ameliorate this symptom. In the process of distraction osteogenesis, the fiber matrix in the suture acts as a mechanical sensor. Compared with osteogenesis, the formation of collagen fibers by fibroblasts is significant in the early stage of sutural distraction. However the transformation of fibroblasts during sutural bone formation induced by tensile force is poorly characterized. Here, we used single-cell RNA sequencing to define the cell classification of the zygomatic maxillary suture and the changes of cell clusters in the suture before and after seven-day distraction. We identified twenty-nine cell subsets spanning monocyte/macrophages, neutrophils, red blood cells, B cells and fibroblasts. Compared with the control group, Monocle analysis revealed the emergence of a unique fibroblast subset (Cdh5+, Col4a1+, Fat1-, and Acta2-) (cluster 27) that expressed vascular endothelial cell genes within the distracted zygomatic maxillary suture. We constructed the differentiation trajectories of the fibroblast population (cluster 23, 27) in the suture before and after distraction. In addition, we clarified that a subset of fibroblasts (cluster 27) lost expression of Fat1, an upregulator of the Hippo pathway, and upregulated Cyr61, a downstream gene of the Hippo pathway, during the distraction process. Further enrichment analysis suggests that cells of the new subset (cluster 27) are undergoing conversion of their identity into a vascular endothelial cell-like state in response to mechanical stimulation, associated with upregulation of angiogenesis genes along the single-cell trajectory. Further immunofluorescence staining confirmed this phenomenon. A combined general transcriptome RNA sequencing data analysis demonstrated that the fibroblasts expressed a number of extracellular matrix-related genes under mechanical strain. These data together provide a new view of the role of fibroblasts in tension-induced sutural angiogenesis via interaction with the Hippo pathway.

Negative regulation of endothelin signaling by SIX1 is required for proper maxillary development.

Jaw morphogenesis is a complex event mediated by inductive signals that establish and maintain the distinct developmental domains required for formation of hinged jaws, the defining feature of gnathostomes. The mandibular portion of pharyngeal arch 1 is patterned dorsally by Jagged-Notch signaling and ventrally by endothelin receptor A (EDNRA) signaling. Loss of EDNRA signaling disrupts normal ventral gene expression, the result of which is homeotic transformation of the mandible into a maxilla-like structure. However, loss of Jagged-Notch signaling does not result in significant changes in maxillary development. Here we show in mouse that the transcription factor SIX1 regulates dorsal arch development not only by inducing dorsal Jag1 expression but also by inhibiting endothelin 1 (Edn1) expression in the pharyngeal endoderm of the dorsal arch, thus preventing dorsal EDNRA signaling. In the absence of SIX1, but not JAG1, aberrant EDNRA signaling in the dorsal domain results in partial duplication of the mandible. Together, our results illustrate that SIX1 is the central mediator of dorsal mandibular arch identity, thus ensuring separation of bone development between the upper and lower jaws.

Impact of different types of facial nerve reconstruction on the recovery of motor function: an experimental study in adult rats.

OBJECTIVE: Poor functional recovery after facial nerve reconstruction is characterized by mass movements and synkinesis. Major reasons are axonal sprouting from the regenerating axons leading to misdirected reinnervation and hyperinnervation as well as polyinnervation of the mimic muscle end plates. We analyzed whether or not the type of nerve reconstruction influenced these pathological phenomena. METHODS: The experiments were performed on 48 adult rats divided into four groups. One group served as an intact control and the experimental groups were subjected to facial-facial nerve repair (FFN), facial nerve interpositional grafting, and hypoglossal-facial nerve repair (HFN), with 12 subjects in each group. Two months later, functional recovery was measured by biometrical motion analysis of whisking. Retrograde fluorescence labeling of the brainstem motoneurons was used to quantify the degree of collateral axonal branching at the lesion site. Fluorescence histochemistry of sections through the levator labii superioris muscle was performed to quantify the degree of polyinnervation after surgery. RESULTS: The type of nerve reconstruction significantly influenced the regeneration. The whisking amplitude did not recover completely regardless of the type of reconstruction. The angular velocity and angular acceleration of the vibrissal hairs showed a full recovery after facial nerve interpositional grafting and HFN, whereas these parameters remained decreased after FFN. Significantly less collateral branching and polyinnervation of the end plates were determined after grafting and HFN than after FFN. CONCLUSION: No type of immediate facial nerve reconstruction results in a full recovery in the rat. However, the morphological and functional recovery was significantly better after grafting and HFN than after FFN.