Analysis of the FGFR spatiotemporal expression pattern within the chicken scleral ossicle system.

Fibroblast Growth Factors (FGFs) play several important roles during organ morphogenesis and act as multi-functional growth factors that bind to their membrane bound receptors (FGFRs) and activate further downstream signalling pathways. Several studies have investigated the function and expression of FGF/FGFRs in endochondral bone development, however, we know little about their role in the development of neural crest derived intramembranous bones. Here, we investigate the expression of 'b' and c' isoforms of FGFRs 1-3 during the development of the scleral ossicles, a ring of neural crest derived intramembranous bones in the chicken eye. These bones are induced by conjunctival papillae. We identified the expression of both 'b' and 'c' isoforms of FGFRs1-3 during phase 1 of ossicle development when conjunctival papillae development takes place. In contrast, during phase 2, when skeletal condensations are induced in the mesenchyme, all isoforms were downregulated. This data shows for the first time the presence of FGFRs in the chicken sclera, thus implicating FGFs as a signalling pathway potentially involved in scleral ossicle development.