FGFR3 is a positive regulator of osteoblast expansion and differentiation during zebrafish skull vault development

Gain- or loss-of-function mutations in fibroblast growth factor receptor 3 (FGFR3) result in cranial vault defects - highlighting the proteins role in membranous ossification. Zebrafish express high levels of fgfr3 during skull development; in order to study FGFR3s role in cranial vault development, we generated the first fgfr3 loss-of-function zebrafish (fgfr3lof/lof). The mutant fish exhibited major changes in the craniofacial skeleton, with a lack of sutures, abnormal frontal and parietal bones, and the presence of ectopic bones. Integrated analyses (in vivo imaging, and single-cell RNA sequencing of the osteoblast lineage) of zebrafish fgfr3lof/lof revealed a delay in osteoblast expansion and differentiation, together with changes in the extracellular matrix. These findings demonstrate that fgfr3 is a positive regulator of osteogenesis. We hypothesize that changes in the extracellular matrix within growing bone impair cell-cell communication, mineralization, and new osteoblast recruitment.