Intravitreal injection of FGF and TGF-β inhibitors disrupts cranial cartilage development

Cartilage development is a tightly regulated process that requires the interaction of epithelial and mesenchymal tissues layers to initiate the aggregation of mesenchyme in a condensation. Several signaling molecules have been implicated in cartilage formation including FGFs, WNTs, and members of the TGF-β super family. However, little is known about the earliest signals involved in these initial phases of development. Here we aimed to investigate whether direct intravitreal injection of pharmaceutical inhibitors for FGF and TGF-β signaling would perturb cranial cartilages in zebrafish. Via wholemount bone and cartilage staining, we found effects on multiple cranial cartilage elements. We found no effect on scleral cartilage development, however, the epiphyseal bar, basihyal, and basicapsular cartilages were disrupted. Interestingly, the epiphyseal bar arises from the same progenitor pool as the scleral cartilage, namely, the periocular ectomesenchyme. This study adds to the foundational knowledge about condensation induction of cranial cartilage development and provides insight into the timing and signaling involved in the early development of several craniofacial cartilage elements in zebrafish.